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Neuromuscular Differences Between Endurance-Trained, Power-Trained, and Sedentary Subjects
Abstract
This study tested the hypothesis that neuromuscular characteristics of plantar flexor (PF) and knee extensor (KE) muscles explain differences of both performance in vertical jump and maximal voluntary isometric contraction (MVC) between endurance-trained (END, n = 9), power-trained (POW, n = 8), and sedentary subjects (SED, n = 8). Evoked twitch characteristics of PF and KE were measured. MVC, maximal voluntary activation (%VA) of KE, and performance in vertical jump were also measured. POW have higher maximal rate of twitch force development (MRFD) than SED and END for both PF (p < 0.05) and KE (p < 0.01); %VA and MVC were higher for POW and END than SED (p < 0.01). Higher performances were measured in vertical jump for POW compared with END and SED. Significant relationships were found between the squat jump performance and MRFD for both KE and PF (R = 0.71, p < 0.0001 and R = 0.55, p < 0.01, respectively). These findings show that low MRFD on lower limbs extensors does not limit expression of MVC on subjects with high levels of activation, whereas intrinsic muscular qualities have a direct influence on performance during the vertical jump.
... This method has obvious flaws (e.g., impact of genetics, uncontrolled type, and amount of training) but it also has one main advantage: it allows examination of training adaptations due to several years of training as opposed to several weeks (generally [3][4][5][6][7][8][9][10][11][12] in interventional studies, i.e., a very limited time period compared to an athlete's or patient's life. Lattier et al. [40] showed that although power-trained athletes (POW) performed much better for squat jumps than endurance-trained athletes (END), the two groups were equally strong for isometric MVC. Also, both groups were stronger than sedentary subjects (SED). ...
... The difference might be due to a significantly lower VA in SED while VA was similar between END and POW. The results of Lattier et al. [40] were confirmed by Garrandes et al. [41], who did not find any difference in knee-extensor VA, measured with the interpolated twitch technique, between END and POW. This suggests that both POW and END athletes are equally capable of maximally driving their muscles when activation is measured in isometric conditions. ...
... Although VA was not reported in this study, it is very unlikely that VA was lower in SED than in END. However, both Lattier et al. and Cohen et al. [40,42] observed a lack of difference in squat jump and rate of force development (RFD) for SED and END. It has also been shown that even when force is expressed as a percentage of maximum, the force-time curves of POW were faster than END. ...
Neural adaptations induced by strength training have been widely described although recent technical developments (e.g., transcranial magnetic stimulation) have provided new insights. Neural adaptations to endurance training are not as well-known and usually considered to be much smaller than those observed following strength training. In this chapter, we will not use the real definition of endurance, that is the ability to sustain a high percentage of maximal oxygen uptake (V̇O2max). Instead, we will use common usage of the word endurance, i.e., prolonged, low-intensity exercise, usually with large muscle mass such as cycling, running, and cross-country skiing. The theory behind chronic adaptations is related to acute deleterious effects and recovery (e.g., [1, 2]). In the first part of this chapter, the tools used to assess neural adaptations will be briefly described. Then, we will focus on the acute neural responses induced by a single endurance training session. Special consideration will be given to the difference between endurance running and cycling/cross-country skiing at the end of this second section. The third part of this chapter will be dedicated to chronic adaptations to the neural command induced by endurance training.
... As expected and in accordance with previous literature, trained athletes exhibited greater plantar flexors isometric MVC force compared to untrained individuals (Lattier et al. 2003;Tillin et al. 2010). The difference between traceurs and non-trained participants was even greater when assessing a more specific performance such as the RTD. ...
... To assess muscle characteristics, the mechanical twitch properties is a common and useful tool that was used to compare untrained and trained individuals [e.g. (Maffiuletti et al. 2001;Lattier et al. 2003;Garrandes et al. 2007)]. In the present study, plantar flexors twitches exhibited different time characteristics (higher rate of torque development, lower contraction and half relaxation times) and greater peak value (Pt) in traceurs than in untrained individuals. ...
... These twitch characteristics can be explained by several factors, such as (1) structural differences, e.g. larger cross-sectional area of lower limb muscles in power-athletes compared to untrained individuals (Häkkinen and Keskinen 1989;Sleivert et al. 1995) or greater fast (type II) to slow (type I) fiber ratio (Clarkson et al. 1980;Staron et al. 1984; Sleivert et al. (2) different muscle intracellular processes, such as greater myosin ATPase activity (Pääsuke et al. 1999;Lattier et al. 2003). While muscle structural changes would have affected both resting and potentiated twitches in a similar extent between traceurs and untrained, the present results showed a greater inter-group difference in resting twitch and no significant change in potentiated twitch. ...
Purpose:
Practising a power-type activity over years can shape the neuromuscular profile of athletes. This study aimed at comparing the neuromuscular profile of a non-trained group (NT, n = 10) to power athletes practising Parkour (= traceurs, group PK, n = 11), an activity consisting of jumping obstacles mostly in an urban landscape.
Methods:
Maximal isometric plantar flexion force (MVC) and rate of torque development (RTD) were evaluated, and neuromuscular function of triceps surae muscles was assessed and compared between groups through the analysis of evoked potentials from posterior tibial nerve stimulation.
Results:
PK group exhibited higher MVC force (131.3 ± 8.7 Nm) than NT (110.4 ± 9.6 Nm, P = 0.03) and higher RTD (489.1 ± 93 Nm/s) than NT (296.9 ± 81 Nm/s). At a nervous level, this greater performance was related to a greater voluntary activation level (PK: 96.8 ± 3.6%; NT: 91.5 ± 7.7%; P = 0.02) and soleus V-wave amplitude (P = 0.03), and a lower antagonist co-activation (P = 0.02) and rest soleus spinal excitability (PK Hmax/Mmax: 0.32 ± 0.13; NT: 0.58 ± 0.17; P < 0.001). At a muscular level, PK group exhibited higher mechanical twitch amplitude (PK: 13.42 ± 3.52 Nm; NT: 9.86 ± 4.38 Nm; P = 0.03) and electromechanical efficiency (P = 0.04).
Conclusions:
The greater maximal force production capacity of traceurs compared to untrained was underlain by nervous factors, such as greater descending command and greater ability to modulate the spinal excitability, but also by muscular factors such as greater excitation-contraction coupling efficiency. The high eccentric loads that characterize Parkour training may have led traceurs to exhibit such neuromuscular profile.
... Strength and endurance athletes are noticeably different from each other in physiological, morphological, and performance aspects (Costill et al., 1976;Hawley, 2009;Lattier et al., 2003). Albeit neural aspects (e.g., number and type of motor units recruited) play a significant role during the execution of different types of physical activity (Sale, 1987), muscle contractile properties (e.g., intrinsic muscular qualities) are key determinants of performance in both strength and endurance athletes (Costill et al., 1976;García-García et al., 2015;Lattier et al., 2003;Loturco et al., 2015). ...
... Strength and endurance athletes are noticeably different from each other in physiological, morphological, and performance aspects (Costill et al., 1976;Hawley, 2009;Lattier et al., 2003). Albeit neural aspects (e.g., number and type of motor units recruited) play a significant role during the execution of different types of physical activity (Sale, 1987), muscle contractile properties (e.g., intrinsic muscular qualities) are key determinants of performance in both strength and endurance athletes (Costill et al., 1976;García-García et al., 2015;Lattier et al., 2003;Loturco et al., 2015). Accordingly, sprinters have a faster fiber type dominance, which favors a powerful muscle contraction in comparison with endurance runners, which in the other hand show higher proportion of slow fiber type (Costill et al., 1976). ...
... There is evidence that the functional differences observed between athletes from sports of distinct physiological requirements are partly due to genetic endowment, as well as to training specific adaptations (Lattier et al., 2003). Endurance training stimulates several metabolic adaptations in trained muscle fibers, such as increased mitochondrial content, slower rate of glycogen utilization and greater reliance on fat oxidation. ...
... Such adaptation may alter the recruitment of motor units during submaximal and maximal muscle contractions. Consequently, Lattier et al. (2003) compared the ability of endurance-and strength-trained individuals to maximally activate their motor units but did not find any difference between populations. However, compared to sedentary subjects, both groups displayed higher activation levels, suggesting that both strength and endurance training are able to increase the maximal activation level of motor units. ...
... However, compared to sedentary subjects, both groups displayed higher activation levels, suggesting that both strength and endurance training are able to increase the maximal activation level of motor units. The results of Lattier et al. (2003) were confirmed by Garrandes et al. (2007) who did not find any difference in voluntary activation levels of the knee extensor (KE) muscles, measured with the twitch interpolation technique, between endurance-and power-trained athletes. It can therefore be suggested that endurance training would induce an increase in the maximal activation level. ...
... Such findings agree with those of Morrison et al. (2006), who did not find any significant difference in activation levels between groups with different aerobic fitness levels, and those of Vila-Cha et al. (2012), who reported unchanged V-wave amplitudes after endurance training. However, Lattier et al. (2003) and Garrandes et al. (2007) reported that endurance-trained subjects have higher activation levels compared to sedentary subjects. The discrepancy of these findings and the absence of adaptations at the neural level in the current study may be ascribed either (1) to a selection bias, (2) to the characteristics of the endurance-training program, or (3) to the specificity of the evaluation of neuromuscular function. ...
The aim of this study was to investigate the neural adaptations to endurance training, and more specifically the adaptation of the cortical voluntary activation of the knee extensor (KE) muscles.
Sixteen sedentary men were randomly allocated into an endurance training (n = 8) or a control group (n = 8). All subjects performed a maximal aerobic speed test (MAS) before and immediately after the training period. Training lasted 8 weeks and was based on endurance running. During Pre- and Post-training testing sessions, maximal voluntary contraction (MVC) was measured and voluntary activation (VA) was calculated via peripheral nerve (PNS) and transcranial magnetic stimulations (TMS) superimposed to MVC. Electromyographic activity (EMG) of the KE muscles was also measured during MVC, PNS (M-wave) and TMS (motor evoked potentials-MEP). The cortical silent period following TMS was also assessed.
Despite a significant improvement in endurance running performance, as suggested by the increase of MAS in the training group (Pre 15.4 ± 1.6 vs. Post 16.4 ± 1.6 km·h(-1)), endurance training did not affect MVC or VA as measured with PNS and TMS. Similarly, the EMG of KE muscles during MVC did not show any significant changes. Furthermore, the MEP amplitude and the duration of the silent period also remained unchanged after endurance training.
The present study suggests an 8-week endurance-training program does not generate adaptations of neural factors in sedentary subjects.
... However, to analyse long-term training adaptations in humans, cross-sectional studies have generally been used. Some of these experiments have focused on differences in the neuromuscular system of powertrained and endurance-trained athletes (Kyrö läinen & Komi, 1994;Lattier, Millet, Maffiuletti, Babault, & Lepers, 2003;Maffiuletti et al., 2001;Sleivert, Backus, & Wenger, 1995), illustrating that systematic exercise training induces specific processes of adaptation in the neuromuscular system depending on the type of physical activity performed. ...
... The measurement of twitch contractile properties of athletes' muscles has been used for the analysis of specificity adaptation of the neuromuscular system to various types of systematic training (Alway, MacDougall, & Sale, 1989;Lattier et al., 2003;Maffiuletti et al., 2001;Pääsuke, Ereline & Gapeyeva, 1998, 1999Sale, Upton, McComas, & MacDougall, 1983;Sleivert et al., 1995). By using electrically evoked supramaximal isometric twitch characteristics, the contractile properties of human skeletal muscles, independent of control and activation by the nervous system, can be determined. ...
... Twitch contractile properties have been shown to differ in heavy resistance-trained athletes compared with sedentary individuals (Sale et al., 1983) and in power-trained athletes compared with endurancetrained athletes and sedentary individuals (Lattier et al., 2003;Maffiuletti et al., 2001;Pääsuke et al., 1998Pääsuke et al., , 1999. Our previous research indicates that power training induces a more evident increase of force-generating capacity and speed of contraction and relaxation in plantarflexor muscles than endurance training (Pääsuke et al., 1998(Pääsuke et al., , 1999. ...
Abstract
The purpose of this study was to compare twitch contractile properties of skeletal muscles in male athletes who train for
power and endurance simultaneously (Nordic combined athletes) with athletes who train for endurance (cross-country
skiers) and sedentary individuals. Ten Nordic combined athletes, 13 cross-country skiers, and 14 sedentary males aged
20�26 years participated. To determine the contractile properties of the plantarflexor muscles during isometric twitch, the
posterior tibial nerve in the popliteal fossa was stimulated by supramaximal square wave pulses of 1 ms duration. Twitch
peak force, maximal rates of force development and relaxation, contraction and half-relaxation times were measured. The
percentage increase in twitch peak force after a 5-s maximal voluntary contraction (MVC) was taken as an indicator of postactivation
potentiation. Nordic combined athletes had a significantly greater twitch post-activation potentiation
and rate of force development and shorter contraction time than the other two groups (PB0.05). They also had a greater
(PB0.05) twitch peak force than cross-country skiers. No significant differences in measured twitch contraction
characteristics were found in cross-country skiers and sedentary males. We conclude that the twitch contractile properties
of the plantarflexor muscles differed markedly in athletes who train for power and endurance simultaneously compared with
athletes who predominantly train for endurance. As an indicator of long-term adaptation to simultaneous power and
endurance training, increased twitch force-generation and potentiation capacity, and shortening of twitch contraction times
in the plantarflexor muscles were observed in Nordic combined athletes.
... The effects of endurance training on muscle performance have been investigated to a limited extent in adults, demonstrating either no change 6 or some enhancement in muscle maximal and explosive strength. 7,8 No comparable data are available for children. ...
... Endurance training may affect muscle morphology in young adults by generally changing the myosin heavy-chain isoform expression from fast to slow. 14 Whereas endurance training has been shown to be associated with some neural adaptations in adults, 8 to our knowledge, the effects of such training on muscle morphology or neural response has not been examined in children. ...
... 31 Some investigators have even found endurance-trained athletes to be stronger than untrained counterparts. 8 However, in the latter study, muscle strength was not scaled to body size. A recent study which examined the effects of different types of training on muscle strength in young adults 32 suggests that endurance training actually hinders the development of lower-extremity strength and, particularly, explosive power development. ...
Previous studies in adults have demonstrated power athletes as having greater muscle force and muscle activation than nonathletes. Findings on endurance athletes are scarce and inconsistent. No comparable data on child athletes exist.
This study compared peak torque (Tq), peak rate of torque development (RTD), and rate of muscle activation (EMG rise, Q30), in isometric knee extension (KE) and flexion (KF), in pre- and early-pubertal power- and endurance-trained boys vs minimally active nonathletes.
Nine gymnasts, 12 swimmers, and 18 nonathletes (7-12 y), performed fast, maximal isometric KE and KF. Values for Tq, RTD, electromechanical delay (EMD), and Q30 were calculated from averaged torque and surface EMG traces.
No group differences were observed in Tq, normalized for muscle cross-sectional area. The Tq-normalized KE RTD was highest in power athletes (6.2 ± 1.9, 4.7 ± 1.2, 5.0 ± 1.5 N·m·s-1, for power, endurance, and nonathletes, respectively), whereas no group differences were observed for KF. The KE Q30 was significantly greater in power athletes, both in absolute terms and relative to peak EMG amplitude (9.8 ± 7.0, 5.9 ± 4.2, 4.4 ± 2.2 mV·ms and 1.7 ± 0.8, 1.1 ± 0.6, 0.9 ± 0.5 (mV·ms)/(mV) for power, endurance, and nonathletes, respectively), with no group differences in KF. The KE EMD tended to be shorter (P = .07) in power athletes during KE (71.0 ± 24.1, 87.8 ± 18.0, 88.4 ± 27.8 ms, for power, endurance, and nonathletes), with no group differences in KF.
Pre- and early-pubertal power athletes have enhanced rate of muscle activation in specifically trained muscles compared with controls or endurance athletes, suggesting that specific training can result in muscle activation-pattern changes before the onset of puberty.
... The lower RFD in children could be explained by fibre type differences or by differences in the rate of muscle activation between children and adults. Power training in adults has been shown to increase muscle strength, RFD and the rate of activation (Aagaard et al 2002, Lattier et al. 2003) In children resistance training is known to increase strength with little or no hypertrophy, possibly due to neural mechanisms (Falk and Tenenbaum 1996) little is know about the effect of training or RFD in children. The purpose of this study was to examine the interaction between maturation and power training on muscle strength, activation and RFD. ...
... Adults who are power-trained show similar training adaptations to resistance-trained adults. These adaptations include greater strength and RFD, when compared with the untrained population (Lattier et al. 2003). Often, power training is thought of as only Olympic style weightlifting and plyometrics. ...
... Using this technique, small increases in muscle activation have been demonstrated in adults after resistance training (Knight and Kamen 2001). Likewise, differences between power-trained and sedentary men have also been shown (Lattier et al. 2003). Enhanced muscle activation in the trained men could explain the differences in peak torque observed between the trained and untrained men in the current study. ...
During maturation, muscle strength is enhanced through muscle growth, although neuro-muscular factors are also believed to be involved. In adults, training for power sports has been shown to enhance muscle strength and activation. The purpose of this study was to examine muscle strength and activation in power-trained athletes (POW) compared with non-athletes (CON), in boys and in adults. After familiarization subjects performed ten 5-s explosive maximal voluntary contractions for elbow and knee flexion and extension. The adults were stronger then the boys and the adult POW were stronger then the adult CON, even after correction for muscle size. Normalized rate of torque development was higher in the adults then in the boys and higher in the POW then CON boys. The rate of muscle activation was higher in the adults and POW groups. The results suggest that maturation and power-training have an additive effect on muscle activation.
... However, data on the effect of endurance training on strength and neuromuscular adaptations are limited. While some evidence exists demonstrating increased muscle activation and possibly increased strength in endurance athletes compared with untrained adults (Lattier et al. 2003; Lucia et al. 2000), there are no comparable data in children. That is, the neuromuscular adaptations to endurance training in children have not been examined. ...
... Those studies have used different instruments to measure maximal strength and power, therefore a comparison between the studies is challenging. Nevertheless, it is well established that endurance-trained athletes have lower maximal strength compared with power athletes (Izquierdo et al. 2002; Sleivert et al. 1995; Ullrich & Bruggemann, 2008; Lattier et al. 2003; Kyrolainen & Komi, 1994). However, conflicting evidence exists regarding the differences in maximal strength between endurance-trained athletes and sedentary individuals. ...
... However, conflicting evidence exists regarding the differences in maximal strength between endurance-trained athletes and sedentary individuals. While some cross-sectional studies (Sleivert et al. 1995; Kanehisa et al. 1997), and training studies (Hickson, 1980; McCarthy et al. 2002; Grandys et al. 2008), reported no difference between the two populations in maximal strength, other studies reported endurance athletes to be stronger than their untrained counterparts (Izquierdo et al. 2002; Lattier et al. 2003). These discrepancies could be possibly attributed to different types of contractions tested, different equipment used, and training levels and backgrounds of the athletes. ...
Competitive sports participation in youth is becoming increasingly more common in the Western world. It is widely accepted that sports participation, specifically endurance training, is beneficial for physical, psychomotor, and social development of children. The research on the effect of endurance training in children has focused mainly on healthrelated benefits and physiological adaptations, particularly on maximal oxygen uptake. However, corresponding research on neuromuscular adaptations to endurance training and the latter's possible effects on muscle strength in youth is lacking. In children and adults, resistance training can enhance strength and mcrease muscle activation. However, data on the effect of endurance training on strength and neuromuscular adaptations are limited. While some evidence exists demonstrating increased muscle activation and possibly increased strength in endurance athletes compared with untrained adults, the neuromuscular adaptations to endurance training in children have not been examined. Thus, the purpose of this study was to examine maximal isometric torque and rate of torque development (RID), along with the pattern of muscle activation during elbow and knee flexion and extension in muscle-endurancetrained and untrained men and boys. Subjects included 65 males: untrained boys (n=18), endurance-trained boys (n=12), untrained men (n=20) and endurance-trained men (n=15). Maximal isometric torque and rate of torque development were measured using an isokinetic dynamometer (Biodex III), and neuromuscular activation was assessed using surface electromyography (SEMG). Muscle strength and activation were assessed in the dominant arm and leg, in a cross-balanced fashion during elbow and knee flexion and extension. The main variables included peak torque (T), RTD, rate of muscle activation (Q30), Electro-mechanical delay (EMD), time to peak RTD and co-activation index. Age differences in T, RTD, electro-mechanical delay (EMD) and rate of muscle activation (Q30) were consistently observed in the four contractions tested. Additionally, Q30, nonnalized for peak EMG amplitude, was consistently higher in the endurancetrained men compared with untrained men. Co-activation index was generally low in all contractions. For example, during maximal voluntary isometric knee extension, men were stronger, had higher RTD and Q30, whether absolute or nonnalized values were used. Moreover, boys exhibited longer EMD (64.8 ± 18.5 ms vs. 56.6 ± 15.3 ms, for boys and men respectively) and time to peak RTD (112.4 ± 33.4 ms vs. 100.8 ± 39.1 ms for boys and men, respectively). In addition, endurance-trained men had lower T compared with untrained men, yet they also exhibited significantly higher nonnalized Q30 (1.9 ± 1.2 vs. 1.1 ± 0.7 for endurance-trained men and untrained men, respectively). No training effect was apparent in the boys. In conclusion, the findings demonstrate muscle strength and activation to be lower in children compared with adults, regardless of training status. The higher Q30 of the endurance-trained men suggests neural adaptations, similar to those expected in response to resistance training. The lower peak torque may su9gest a higher relative involvement oftype I muscle fibres in the endurance-trained athletes. Future research is required to better understand the effect of growth and development on muscle strength and activation patterns during dynamic and sub-maximal isometric contractions. Furthennore, training intervention studies could reveal the effects of endurance training during different developmental stages, as well as in different muscle groups.
... It has been shown that power-trained athletes produce higher maximal voluntary force than endurancetrained athletes. This difference can be attributed to central regulation involving the agonist muscle activation level and antagonist muscle coactivation (3) and/or to peripheral adaptations including muscle cross-sectional area (9,28), type II/I fiber area ratios (28), and muscle contractile properties (19,27). Moreover, within an endurance-trained group, the type of locomotion may vary with the specific sport and further influence the neuromuscular profile. ...
... These differences at preexercise have already been reported and are probably related to a larger muscle cross-sectional area in powertrained athletes than in endurance athletes (9,28) and to a greater type II/type I fiber area ratio in EXPLO compared with ENDU (28). Moreover, the larger Pt paired noted in EXPLO at preexercise could be explained by a higher twitch rate of force development involving greater myosin ATPase activity (19,27). ...
... The voluntary activation of the knee extensor muscles, estimated by the interpolated twitch method, did not significantly differ between groups before the fatiguing exercise. This agrees with the findings of a previous study that showed identical levels of activation in power-and endurance-trained athletes (19). The lack of a significant decrease in voluntary activation after our fatiguing exercise in any of the groups suggests that central changes did not contribute to the isometric torque decrease observed for EXPLO. ...
This study examined the effects of training background on the relationship between the neuromuscular fatigue profile and maximal voluntary torque production in isometric, concentric, and eccentric contraction modes.
Before and after three sets of 31 isokinetic concentric knee extensions at 60 degrees .s(-1), voluntary and electrically induced contractions were recorded in 14 endurance-trained (ENDU) men (seven cyclists: age 25 +/- 2 yr, mass 70 +/- 8 kg, height 175 +/- 5 cm; and seven triathletes: age 27 +/- 4 yr, mass 71 +/- 5 kg, height 179 +/- 6 cm) and seven explosive power-trained men (EXPLO: age 24 +/- 1 yr, mass 73 +/- 5 kg, height 179 +/- 4 cm). Maximal knee-extension torque, activation level (twitch interpolation technique), electromyographic activity of agonist and antagonist muscles, and twitch contractile properties were assessed.
At preexercise, the maximal voluntary isometric and concentric torques of EXPLO were greater than those of ENDU (P < 0.05). After the fatiguing exercise, significant isometric (18%; P < 0.01) and concentric (25%; P < 0.05) torque decreases in EXPLO were associated with, respectively, twitch torque (Pt) and maximal rate of twitch development (+dPt/dt) reductions (P < 0.01) and with an increase in the antagonist coactivation level (P < 0.01). No modification was observed for ENDU. Interestingly, the coactivation level was also increased (P < 0.01) in eccentric contraction for EXPLO, although the maximal eccentric torque decrease (P < 0.01) could not be specifically attributed to any group.
The fatiguing exercise induced central and peripheral adaptations, but the mechanisms differed regarding the contraction mode. At pre- and postfatiguing exercise, it seems that the neuromuscular profile depends on the subject's training background and the contraction modes used to assess fatigue.
... However, their assessment is mostly incomplete because the neuromuscular origins of physical capacities (neural vs. muscular) are rarely evaluated in order to be considered throughout youth sports training programs. In addition, while neuromuscular characteristics differ markedly between adults who perform different sports (endurancetrained vs. power-trained) partly because of genetic predisposition and their training history (Lattier et al. 2003), it has yet to be ascertained whether such differences already manifest by early adolescence. This may prove central to talent identification and influence the training strategies adopted for succeeding in a sport requiring specific neuromuscular characteristics during adolescence (strength vs. endurance). ...
... Untrained controls (CON) included 12 adolescents practicing less than 2 h of deliberate physical activity per week. The sample size estimation was determined for a two-sided type I error at 5% and a statistical power greater than 80% on the basis of previously published data on MVIC torque of the knee extensors in endurancetrained, power-trained and untrained adults (Lattier et al. 2003). The three groups were matched for chronological age and maturity status. ...
Introduction
Although neuromuscular function varies significantly between strength and endurance-trained adult athletes, it has yet to be ascertained whether such differences manifest by early adolescence. The aim of the present study was to compare knee extensor neuromuscular characteristics between adolescent athletes who are representative of strength (wrestling) or endurance (triathlon) sports.
Methods
Twenty-three triathletes (TRI), 12 wrestlers (WRE) and 12 untrained (CON) male adolescents aged 13 to 15 years participated in the present study. Maximal voluntary isometric contraction (MVIC) knee extensor (KE) torque was measured, and 100-Hz magnetic doublets were delivered to the femoral nerve during and after KE MVIC to quantify the voluntary activation level (%VA). The doublet peak torque (T100Hz) and normalized vastus lateralis (VL) and rectus femoris (RF) EMG (EMG/M-wave) activities were quantified. VL and RF muscle architecture was also assessed at rest using ultrasound.
Results
Absolute and relative (to body mass) KE MVIC torques were significantly higher in WRE than TRI and CON (p < 0.05), but comparable between TRI and CON. No significant differences were observed between groups for %VA, T100Hz or either VL or RF muscle thickness. However, VL EMG/M-wave was higher, RF fascicle length longer, and pennation angle smaller in WRE than TRI and CON (all p < 0.05).
Conclusion
The wrestlers were stronger than triathletes and controls, potentially as a result of muscle architectural differences and a greater neural activation. Neuromuscular differences can already be detected by early adolescence in males between predominantly endurance and strength sports, which may result from selection bias and/or physical training.
... Endurance athletes have capacity to produce skeletal muscle contractions at lower force and velocities but are more resistant to fatigue during submaximal motor tasks, whereas power athletes can develop greater muscle force and higher velocities but fatigue more rapidly [1,2]. These differences in muscle contractility arise from a combination of inherited and acquired neuromuscular characteristics of each individual athlete [2]. ...
... Endurance athletes have capacity to produce skeletal muscle contractions at lower force and velocities but are more resistant to fatigue during submaximal motor tasks, whereas power athletes can develop greater muscle force and higher velocities but fatigue more rapidly [1,2]. These differences in muscle contractility arise from a combination of inherited and acquired neuromuscular characteristics of each individual athlete [2]. The difference in fatigability also exists between muscle groups; the quadriceps femoris (QF) has been shown to be less susceptible to fatigue than the hamstrings [3], mainly due to the difference in muscle fibre content [4]. ...
BACKGROUND: Postactivation potentiation (PAP) enhances contractility of skeletal muscle whereas fatigue deteriorates it. Available evidence suggests that the two phenomena may express differently in endurance and power athletes. OBJECTIVE: To compare the patterns of change in knee muscle contractility induced by PAP and fatigue between endurance and power athletes. METHODS: Eleven endurance and ten power athletes (age: 18–33 years) performed isokinetic fatigue and isometric PAP protocols with knee extensors and flexors on computerised dynamometer. Tensiomyography (TMG) of the vastus medialis and semitendinosus muscle medialis was performed before the protocols and during a 10-min recovery. RESULTS: The changes in TMG profile were most pronounced in the vastus medialis of power athletes following the PAP protocol and least pronounced in the semitendinosus of the endurance athletes following the fatigue protocol. The differences between athlete types were most significant for the time-domain TMG parameters of vastus medialis. A significant correlation (r= 0.51–0.73) between the fatigue indices and changes in TMG parameters was observed for the vastus medialis muscle only. CONCLUSIONS: The results show that the TMG patterns of PAP and fatigue in the vastus muscle differ between endurance and power athletes. In this muscle, the changes in TMG parameters are also strongly associated with the degree of fatigue.
... In trained cyclists (131), runners (125), and cross country skiers (45), greater muscular strength decreases the oxygen cost of locomotion at given absolute intensities irrespective of fiber type distribution (45,106,128). As such, improvements in economy of motion can be achieved through increases in muscle crosssectional area (131) and the efficacy of excitation-contraction coupling (67). Indeed, preserving muscle excitability can prevent impairments in excitation-contraction coupling and metabolic flux rates that would otherwise increase the oxygen cost of a given workload (i.e., reduced economy of motion) during prolonged exercise (1,37). ...
... In contrast to VȮ 2 max and OBLA (25), the impact of BFR training on economy of motion has not been examined. However, BFR-induced improvements in maximal strength (3) and Na 1 -K 1 -ATPase activity (15) indicate a potential benefit to economy of motion as these qualities reduce the oxygen cost of locomotion during prolonged submaximal exercise (67,128). In recreationally active individuals, 4 weeks of cycling (15 minutes, 40% VȮ 2 max) with continuous BFR resulted in a 7.7% increase in maximal knee-extensor force production (i.e., strength) that the authors attributed to the 5.1% increase in quadriceps crosssectional area (2). ...
Smith, NDW, Scott, BR, Girard, O, and Peiffer, JJ. Aerobic training with blood flow restriction for endurance athletes: potential benefits and considerations of implementation. J Strength Cond Res XX(X): 000-000, 2021-Low-intensity aerobic training with blood flow restriction (BFR) can improve maximal oxygen uptake, delay the onset of blood lactate accumulation, and may provide marginal benefits to economy of motion in untrained individuals. Such a training modality could also improve these physiological attributes in well-trained athletes. Indeed, aerobic BFR training could be beneficial for those recovering from injury, those who have limited time for training a specific physiological capacity, or as an adjunct training stimulus to provide variation in a program. However, similarly to endurance training without BFR, using aerobic BFR training to elicit physiological adaptations in endurance athletes will require additional considerations compared with nonendurance athletes. The objective of this narrative review is to discuss the acute and chronic aspects of aerobic BFR exercise for well-trained endurance athletes and highlight considerations for its effective implementation. This review first highlights key physiological capacities of endurance performance. The acute and chronic responses to aerobic BFR exercise and their impact on performance are then discussed. Finally, considerations for prescribing and monitoring aerobic BFR exercise in trained endurance populations are addressed to challenge current views on how BFR exercise is implemented.
... The peak force applied in one cycle in submaximal conditions is more than 5 times higher during running, measured as a ground reaction force (Kyröläinen et al., 1999) than in cycling, measured as a pedal force (Farrell et al., 2003). Also the peak joint moments and power patterns in ankle, knee and hip joints are different during running stance phase than in pedal cycle at steady-state submaximal ( It is known that sprint and endurance training adapt local (single joint) and global (multi joint) muscle strength patterns in different way (Harrisson et al., 2004;Lattier et al., 2003), but how can different types of endurance activities influence muscle strength adaption? Farup et al. (2012) find that 10 weeks endurance cycling training did not change isokinetic strength and force-velocity curve of knee extensors and flexors. ...
... In opposite way, Buśko et al. (2008) conclude that the four week intensive endurance training with different cadences, carried out on the cycle ergometer, caused the increase of the isometric torque of hip extensors, knee extensors and ankle plantar flexors, but lowered the torque of hip flexors and knee flexors. No analogues researches about a local strength adaption in endurance running training were found, but Lattier et al. (2003) compared competitive level endurance runners with sedentary population and did not found significant differences in knee extensors and ankle plantar flexors isometric strength and counter-movement jump performance. Another studies of Kanehisa et al. (1997) and Sleivert et al. (1995) found similar maximal strength and force-velocity values between middle-distance runners and age-matched untrained subjects. ...
... The peak force applied in one cycle in submaximal conditions is more than 5 times higher during running, measured as a ground reaction force (Kyröläinen et al., 1999) than in cycling, measured as a pedal force (Farrell et al., 2003). Also the peak joint moments and power patterns in ankle, knee and hip joints are different during running stance phase than in pedal cycle at steady-state submaximal ( It is known that sprint and endurance training adapt local (single joint) and global (multi joint) muscle strength patterns in different way (Harrisson et al., 2004;Lattier et al., 2003), but how can different types of endurance activities influence muscle strength adaption? Farup et al. (2012) find that 10 weeks endurance cycling training did not change isokinetic strength and force-velocity curve of knee extensors and flexors. ...
... In opposite way, Buśko et al. (2008) conclude that the four week intensive endurance training with different cadences, carried out on the cycle ergometer, caused the increase of the isometric torque of hip extensors, knee extensors and ankle plantar flexors, but lowered the torque of hip flexors and knee flexors. No analogues researches about a local strength adaption in endurance running training were found, but Lattier et al. (2003) compared competitive level endurance runners with sedentary population and did not found significant differences in knee extensors and ankle plantar flexors isometric strength and counter-movement jump performance. Another studies of Kanehisa et al. (1997) and Sleivert et al. (1995) found similar maximal strength and force-velocity values between middle-distance runners and age-matched untrained subjects. ...
The purpose of this study was to compare the isokinetic muscle performance of lower limbs in middle distance runners and road cyclists. Subjects: 10 competitive Estonian middle distance runners (age 23.8 ± 3.8 yrs., height 181.8 ± 2.8 cm, mass 73.6 ± 7.4kg) and 16 road cyclists (21.1 ± 3.5 yrs., 181.5 ± 5.0cm, 74.8 ± 7.0kg) volunteered in this study. Methods: Isokinetic strength of ankle plantar flexors (A-pf), ankle dorsal flexors (A-df), knee (K) and hip (H) extensors (ex) and flexors (fl) were measured with Humac NORM isokinetic dynamometer in angular speeds 60, 180 and 240 °/s. Isokinetic peak torque (PT), and power (P) values of best repetition and total work (ToW) of 15 repetitions in angular speed 240°/s were expressed as a mean of dominant and non-dominant leg. The absolute and relative isokinetic values were compared between runners and cyclists. Results: The comparison of PT values shows that cyclists have significantly (p<0.05) higher results in A-pf and K-fl in all testing speeds. No significant differences between A-df, K-ex, H-fl and H-ex PT values at any speed were found. Cyclists had also significantly higher P results in A-pf, K-fl and K-ex in all testing speeds and tendency (p=0.08) in H-ex 60°/s. ToW values of A-pf, K-ex and K-fl were significantly higher in cyclists group, but runners had higher values in H-fl. Conclusion: Cyclists have higher isokinetic muscle performance values in A-pf, K-fl, and K-ex and runners have higher total work ability in H-fl. No significant differences in A-df and H-ex performance between cyclists and runners were found. Runners and cyclists have also different power-velocity curves of A-df, H-ex, K-ex and K-fl
... To the best of our knowledge, no study has explored the effects of aerobic exercise on strength loss in individuals with different training background. Many studies have demonstrated that strength-trained (ST) athletes produce higher maximal voluntary force than sedentary (SED) and endurance-trained (ET) athletes [13,17,25,29]. This difference can be attributed to both, central regulation [7] and/or to peripheral adaptations including muscle cross-sectional area [13,29], type II/I fiber area ratios [29], and muscle contractile properties [17,25]. ...
... Many studies have demonstrated that strength-trained (ST) athletes produce higher maximal voluntary force than sedentary (SED) and endurance-trained (ET) athletes [13,17,25,29]. This difference can be attributed to both, central regulation [7] and/or to peripheral adaptations including muscle cross-sectional area [13,29], type II/I fiber area ratios [29], and muscle contractile properties [17,25]. As muscle damage evoked by eccentric contractions is found preferentially in type II fibers [9], it stands to reason that ST (greater type II/I fiber area ratios) will present greater strength loss under eccentric condition after aerobic exercise than in SED and ET individuals. ...
The objective of this study was to compare the effects of high intensity running exercise on the strength of the knee extensors at concentric and eccentric conditions in individuals with different training background. Sixteen physically active (SED), 11 endurance-trained (ET) and 7 strength-trained (ST) subjects volunteered to participate in the study. Initially each subject performed, on different days, one familiarization session on an isokinetic dynamometer and an incremental treadmill test to volitional exhaustion to determine the velocity at the onset of blood lactate accumulation (OBLA). The subjects then returned to the laboratory on two experimental sessions, separated by at least five days, to perform maximal isokinetic eccentric (E) and concentric (C) contractions of the quadriceps at 180 • /s. One session was performed after a standardized warm-up period (5 min at 50%VO2max) and the other session was performed after a continuous running at 95% OBLA. The duration of this session was estimated to a caloric expenditure around 500 Kcal. Following this high intensity exercise there was a significant reduction in the peak torque in E in all groups. The percent strength loss in E following the running exercise was statistically higher in ST (16.5%) when compared to SED (6.5%) and ET (7.2%). We thus conclude that the reduction in isokinetic peak torque of the knee extensors after a session of high intensity running exercise at 95% OBLA depends on the contraction type and training background.
... Interestingly, contrary to isometric maximum voluntary strength that can be similar between strength-trained and endurance-trained participants (Lattier et al. 2003), the modulation of antagonist muscles activation is a typical feature of neuromuscular adaptations associated with active engagement in strength training. Several studies have found decreased antagonist muscles activation during isometric contractions in participants engaged in regular strength training (Carolan and Cafarelli 1992;Hakkinen et al. 1998;Hakkinen et al. 2000;Griffin and Cafarelli 2005;Bru and Amarantini 2008). ...
... In the absence of significant difference in voluntary strength between ST and ED participants, which is in line with other studies (Lattier et al. 2003), and in agonist muscles activation, we suggest that the cortical adaptations induced by regular strength training could exert a specific encoding of antagonist muscles. This specific encoding leads to the minimization of antagonist muscles activation and improves the energetic efficiency of the muscle contraction (Baratta et al. 1988;Carolan and Cafarelli 1992;Hakkinen et al. 2000;Bru and Amarantini 2008). ...
During human contraction, net joint torque production involves the contribution of the antagonist muscles. Their activation protects the articulations and facilitates movement accuracy, but despite these fundamental roles, little is known about the brain mechanisms underlying their control. In view of previous studies that showed lesser antagonist muscles activation in participants engaged in regular strength training (ST) than in participants actively engaged in endurance disciplines (ED), we used this between-group comparison to investigate the possible role of motor cortex activity on the control of antagonist muscles. Electroencephalographic (EEG) and electromyographic (EMG) activity as well as the net joint torque were recorded, while ten ST and eleven ED participants performed isometric knee muscles exertions at different force levels. EEG data showed a linear increase in the suppression of cortical oscillations in the 21-31 Hz frequency band with increasing force level in ST but not in ED participants. This effect was associated with lesser EMG activation of the antagonist muscles in ST than in ED participants, the difference between groups also increasing with the force level. Both effects were found specifically during flexion exertions, indicating that ST participants developed sharp central adaptations to control the antagonist muscles involved as prime movers in their usual training task. This result suggests that the cortical adaptations induced by regular strength training could exert a specific encoding of the antagonist muscles, leading to the minimization of their activation and improved energetic efficiency of the muscle contraction.
... Comparable data on the possible effects of endurance training on muscle performance and neuromuscular adaptations are limited. Although some studies suggest increased muscle activation and possibly increased strength in adult endurance athletes compared with untrained adults (Lattier et al. 2003; Lucía et al. 2000), there are no comparable data in children. It has been suggested that the capacity of prepubertal boys to activate their neuromuscular systems is lower than that of adults (Belanger and McComas 1989; Grosset et al. 2008; Hatzikotoulas et al. 2008; O'Brien et al. 2009; Pääsuke et al. 2000), and that children are less capable of recruiting or utilizing their higher-threshold motor units (Asai and Aoki 1996; Falk and Dotan 2006; Falk et al. 2009b). ...
... To the best of our knowledge, this is the first study to examine Q 30 in endurance-trained boys and men. Our results concur with previous studies in adults (Lattier et al. 2003; Lucía et al. 2000 ) that suggested that endurance training increases muscle activation and enhances motor-unit recruitment. However, we feel that because our findings could not correlate performance with Q 30 differences , the relationship between Q 30 and muscle performance is unclear, at least as far as endurance training is concerned. ...
Most research on the effects of endurance training has focused on endurance training's health-related benefits and metabolic effects in both children and adults. The purpose of this study was to examine the neuromuscular effects of endurance training and to investigate whether they differ in children (9.0-12.9 years) and adults (18.4-35.6 years). Maximal isometric torque, rate of torque development (RTD), rate of muscle activation (Q30), electromechanical delay (EMD), and time to peak torque and peak RTD were determined by isokinetic dynamometry and surface electromyography (EMG) in elbow and knee flexion and extension. The subjects were 12 endurance-trained and 16 untrained boys, and 15 endurance-trained and 20 untrained men. The adults displayed consistently higher peak torque, RTD, and Q30, in both absolute and normalized values, whereas the boys had longer EMD (64.7+/-17.1 vs. 56.6+/-15.4 ms) and time to peak RTD (98.5+/-32.1 vs. 80.4+/-15.0 ms for boys and men, respectively). Q30, normalized for peak EMG amplitude, was the only observed training effect (1.95+/-1.16 vs. 1.10+/-0.67 ms for trained and untrained men, respectively). This effect could not be shown in the boys. The findings show normalized muscle strength and rate of activation to be lower in children compared with adults, regardless of training status. Because the observed higher Q30 values were not matched by corresponding higher performance measures in the trained men, the functional and discriminatory significance of Q30 remains unclear. Endurance training does not appear to affect muscle strength or rate of force development in either men or boys.
... Strength training with heavy resistance and a small number of repetitions mobilizes a large part of FT muscle fibres, whereas training with medium resistance and a large number of repetitions mobilizes both FT and ST muscle fibres Jenkins et al., 1984;Johansson et al., 1987;Häkkinen & Keskinen, 1989). It has been found that prolonged heavyresistance strength training and power training do not affect the ratio of FT and ST fibres in muscles (Izquierdo et al., 2002;Lattier et al., 2003), whereas both types of muscle fibres become hypertrophied in the process (Tesch & Karelsson, 1985;Suter et al., 1993;Paavolainen et al., 1994). The cross-sectional area of FT muscle fibres increases more than that of ST muscle fibres, referring to the hypertrophy of the FT muscle fibres. ...
... At the same time, to maintain the oxidative properties of muscles to ensure good aerobic capacity, the strength increase of endurance-trained athletes should be small (1.5% per week) (Rusko, 1987). It has been noted that isometric MVC does not differ significantly in endurance-trained athletes and untrained individuals (Rusko, 1987;Lattier et al., 2003). It has been shown that endurance training significantly increases VO 2 max and the anaerobic threshold in athletes having a large percentage of ST muscle fibres (Rusko & Rahkila, 1983;Sale, 1988;Gerdle et al., 1998). ...
... In the evaluated studies, surface EMG revealed an increased agonist activity during isometric MVC in RT individuals (8,41,98), whereas other studies report no differences (3,61,112). In addition, RT individuals showed to have greater agonist EMG amplitude than UT individuals (79,92,110). ...
Santos, PDG, Vaz, JR, Correia, J, Neto, T, and Pezarat-Correia, P. Long-term neurophysiological adaptations to strength training: a systematic review with cross-sectional studies. J Strength Cond Res XX(X): 000-000, 2023-Neuromuscular adaptations to strength training are an extensively studied topic in sports sciences. However, there is scarce information about how neural mechanisms during force production differ between trained and untrained individuals. The purpose of this systematic review is to better understand the differences between highly trained and untrained individuals to establish the long-term neural adaptations to strength training. Three databases were used for the article search (PubMed, Web of Science, and Scopus). Studies were included if they compared groups of resistance-trained with untrained people, aged 18-40 year, and acquired electromyography (EMG) signals during strength tasks. Twenty articles met the eligibility criteria. Generally, strength-trained individuals produced greater maximal voluntary activation, while reducing muscle activity in submaximal tasks, which may affect the acute response to strength training. These individuals also presented lower co-contraction of the antagonist muscles, although it depends on the specific training background. Global intermuscular coordination may be another important mechanism of adaptation in response to long-term strength training; however, further research is necessary to understand how it develops over time. Although these results should be carefully interpreted because of the great disparity of analyzed variables and methods of EMG processing, chronic neural adaptations seem to be decisive to greater force production. It is crucial to know the timings at which these adaptations stagnate and need to be stimulated with advanced training methods. Thus, training programs should be adapted to training status because the same stimulus in different training stages will lead to different responses.
... Explosive contraction ability is an important sports performance factor (Lattier et al., 2003;Tillin et al., 2010). To date, the rate of torque development is used as a muscle velocity indicator (e.g., Aagaard et al., 2002). ...
This study evaluated the maximal fascicle shortening velocity under near‐no‐load conditions. In addition, we determined whether the rate of torque development during ballistic contraction was related to maximal fascicle shortening velocity. Under passive and active conditions, the medial gastrocnemius muscle fascicle shortening velocity was measured using ultrasonography at 300, 400, 500, 600, 700, 800, 900, and 1000 ° s−1. The maximal fascicle shortening velocity was defined as the fascicle shortening velocity under the lowest angular velocity that satisfied the following two conditions; (1) the difference in torque values between passive and active conditions was below 2.4 Nm and (2) the difference in fascicle shortening velocities between passive and active conditions was below 10 mm s−1. The rate of torque development was analyzed during the periods of 32, 48, 96, 152, and 200 ms after the onset of contraction during ballistic contraction. At the angular velocity (678.6 ± 147.7 ° s−1) that satisfied the two previously mentioned conditions, the exerted torque and the maximal fascicle shortening velocity were 1.4 ± 1.3 Nm and 251.0 ± 40.5 mm s−1. No significant correlations were found between the maximal fascicle shortening velocity and the rate of torque development at each time point. In conclusion, the maximal fascicle shortening velocity was quantified when the angular velocity satisfied the two conditions. Furthermore, the rate of torque development, often used as an indicator of muscle velocity, did not represent the maximal fascicle shortening velocity. The maximal fascicle shortening velocity of human muscles under near no‐load conditions was successfully evaluated when both the exerted torque and the difference in fascicle shortening velocities between passive and active conditions became infinitely small. In addition, the rate of torque development, often used as an indicator of muscle velocity, did not represent the maximal fascicle shortening velocity.
... Par contre, la présence d'une augmentation de la force suite à la stimulation nous indique une activation volontaire incomplète, soulignant une défaillance du système nerveux dans le recrutement des unités motrices et/ou de la fréquence de décharges de celles-ci (Belanger et McComas 1981;Gandevia 2001). Il est d'usage d'observer une activation volontaire incomplète au repos chez les personnes sédentaires (Lattier et al. 2003), âgées (Rozand et al. 2020) ou encore dans certaines pathologies comme chez les PaSEPs . Au cours ou après un exercice fatiguant, il est aussi possible d'observer une diminution de l'activation volontaire, qui révèle la présence d'une fatigue centrale sans qu'on puisse distinguer son origine entre l'étage supra-spinal et l'étage spinal. ...
Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, chronic fatigue being its main symptom. Despite its prevalence in MS, fatigue etiology remains incompletely understood. Moreover, exercise remains the only effective treatment for fatigue, but the effectiveness of a personalized intervention has not been thoroughly investigated. The aim of this PhD project was to characterize the causes of chronic fatigue in people with MS (PwMS) and to compare the benefits of an individualized exercise intervention to a conventional one in fatigued patients. In a first study, we demonstrated the high prevalence of
fatigue in PwMS and the link with physical activity, disability or unemployment status. This first study reinforced the need to investigate fatigue etiology through a more comprehensive list of objective and subjective variables. In the second study, fatigued PwMS showed an increased fatigability, associated with a higher perception of effort, during dynamic whole-body exercise when compared to less fatigued PwMS. Finally, in a third study, we examined the effectiveness of an individualized vs a traditional exercise intervention in fatigued PwMS. Our results showed that the individualized program induced greater benefits, particularly in regards to exercise capacity, than the traditional program. This PhD thesis provides new knowledge on fatigue in MS and suggests potential clinical applications to improve the quality of life of PwMS.
... As observed with other NLMF studies, a contralateral post-fatigue endurance test was more sensitive to NLMF with both the healthy and resistance-trained participants showing significant decrements, whilst the strength-endurance-trained subjects were not significantly affected. The strength-endurance-trained participants could have produced less metabolic by-products due to their lower reliance on glycolytic pathways, resulting in reduced metabolite distribution and diminished inhibitory metaboreceptor afferent input [112]. Thus further investigations should examine whether NLMF can be induced or prevented through the implementation of longitudinal training interventions. ...
Background
The fatigue of a muscle or muscle group can produce global responses to a variety of systems (i.e., cardiovascular, endocrine, and others). There are also reported strength and endurance impairments of non-exercised muscles following the fatigue of another muscle; however, the literature is inconsistent.
Objective
To examine whether non-local muscle fatigue (NLMF) occurs following the performance of a fatiguing bout of exercise of a different muscle(s).
Design
Systematic review and meta-analysis.
Search and Inclusion
A systematic literature search using a Boolean search strategy was conducted with PubMed, SPORTDiscus, Web of Science, and Google Scholar in April 2020, and was supplemented with additional ‘snowballing’ searches up to September 2020. To be included in our analysis, studies had to include at least one intentional performance measure (i.e., strength, endurance, or power), which if reduced could be considered evidence of muscle fatigue, and also had to include the implementation of a fatiguing protocol to a location (i.e., limb or limbs) that differed to those for which performance was measured. We excluded studies that measured only mechanistic variables such as electromyographic activity, or spinal/supraspinal excitability. After search and screening, 52 studies were eligible for inclusion including 57 groups of participants (median sample = 11) and a total of 303 participants.
Results
The main multilevel meta-analysis model including all effects sizes (278 across 50 clusters [median = 4, range = 1 to 18 effects per cluster) revealed a trivial point estimate with high precision for the interval estimate [− 0.02 (95% CIs = − 0.14 to 0.09)], yet with substantial heterogeneity (Q(277) = 642.3, p < 0.01), I² = 67.4%). Subgroup and meta-regression analyses showed that NLMF effects were not moderated by study design (between vs. within-participant), homologous vs. heterologous effects, upper or lower body effects, participant training status, sex, age, the time of post-fatigue protocol measurement, or the severity of the fatigue protocol. However, there did appear to be an effect of type of outcome measure where both strength [0.11 (95% CIs = 0.01–0.21)] and power outcomes had trivial effects [− 0.01 (95% CIs = − 0.24 to 0.22)], whereas endurance outcomes showed moderate albeit imprecise effects [− 0.54 (95% CIs = − 0.95 to − 0.14)].
Conclusions
Overall, the findings do not support the existence of a general NLMF effect; however, when examining specific types of performance outcomes, there may be an effect specifically upon endurance-based outcomes (i.e., time to task failure). However, there are relatively fewer studies that have examined endurance effects or mechanisms explaining this possible effect, in addition to fewer studies including women or younger and older participants, and considering causal effects of prior training history through the use of longitudinal intervention study designs. Thus, it seems pertinent that future research on NLMF effects should be redirected towards these still relatively unexplored areas.
... Il est bien connu que l'entraînement sportif à long terme modifie le profil neuromusculaire des athlètes (Schädler, 1967). Les athlètes explosifs ont par exemple montré un moment maximal volontaire et une secousse mécanique des fléchisseurs plantaires plus importants en comparaison à des sujets endurants (Casabona et al., 1990;Lattier et al., 2003;. Cette spécificité, qui indique une contractilité musculaire différente selon l'expérience sportive, s'exprime aussi au niveau des mécanismes de contrôle du développement de la force. ...
Une pratique intensive de l'entraînement contre résistance, i.e. avec des charges lourdes et un faible nombre de répétitions, peut soumettre les sportifs à des charges d'entraînement élevées qui peuvent conduire à des blessures. Afin d'éviter l'apparition de ces blessures ou de limiter le désentraînement dans le cas contraire, des méthodes alternatives d’entraînement ont été développées. Ces méthodes ont une double cible puisqu'elles permettent aussi de faire pratiquer certaines populations qui, suite à différentes pathologies ou traumatismes, ne peuvent pas s’exercer normalement. Cette thèse s’est intéressée plus particulièrement au système neuromusculaire et aux mécanismes mis en jeu lors du développement de la force sur les muscles fléchisseurs plantaires par imagerie motrice (IM), i.e. la simulation mentale d’un mouvement sans sortie motrice concomitante et par stimulation électrique neuromusculaire (NMES), i.e. évoquer des contractions en appliquant un courant électrique sur le muscle via des électrodes de surface.L’étude I a permis d’obtenir des résultats en faveur de l’existence d’un continuum d’activation neurale du repos à l’IM et de l’IM à la contraction réelle. Au minimum, l’IM pourrait représenter une activation subliminale de structures neurales qui sont partagées avec la contraction. L’étude IIa a montré des gains similaires de force entre des entrainements par NMES et par IM, tous les deux reposant sur des adaptations nerveuses qui, de manière générale, impliquent une plus large part du système corticospinal que ce qui est habituellement attendu, incluant à la fois une plasticité spinale et supraspinale. De manière surprenante, effectuer un entrainement en alternant la NMES et l’IM dans la même session n'a pas mené à des gains de force, montrant qu’un entrainement combiné ne représente pas simplement la somme des gains de chacune des modalités. L’IM et la NMES, en fonction des paramètres choisis, pourraient même montrer des effets concurrents. L’étude IIb a montré que l’IM semble être une méthode d'entraînement efficace pour induire un effet controlatéral, i.e. un gain du membre non-entrainée suivant un entrainement unilatéral de l’autre membre. Au contraire, la NMES avec nos paramètres de stimulation n'a pas mené à un effet controlatéral. Les résultats actuels soulignent le fait que l'effet controlatéral ne nécessite pas forcément une activité du muscle de la jambe entraînée. L’étude III n’a pas permis de mettre en lumière des différences de modulations entre les sujets explosifs, sédentaires et endurants. Une étude parallèle à ce travail de thèse avait mis en lumière des profils neuromusculaires différents entre des sujets explosifs et des sujets sédentaires. Les résultats préliminaires de cette étude peuvent suggérer que la pratique sportive, et plus globalement le profil neuromusculaire d’un sujet, n’influence pas le caractère répondeur ou non-répondeur d’un individu à une sollicitation telle que l’IM.
... Please consider donating at www.storkinesiology.org/annual 18 distribution by the cardiovascular system and diminished inhibitory metaboreceptor afferent input [115]. Though it is not clear whether this could be a result of their prior training history, or due to self-selection bias (i.e. ...
Objective: To examine whether non-local muscle fatigue occurs following performance of a fatiguing bout of exercise of a different muscle(s).
Design: Systematic review and meta-analysis.
Search and Inclusion: A systematic literature search using a Boolean search strategy was conducted with PubMed, SPORTDiscus, Web of Science, and Google Scholar in April 2020 and was supplemented with additional ‘snowballing’ searches up to September 2020. To be included in our analysis, studies had to include at least one intentional performance measure (i.e., strength, endurance, or power), which if reduced could be considered evidence of muscle fatigue, and also had to include the implementation of a fatiguing protocol to a location (i.e., limb or limbs) that differed to those for which performance was measured. We excluded studies that measured only mechanistic variables such as electromyographic, or spinal/supraspinal excitability. After search and screening, 52 studies were eligible for inclusion including 57 groups of participants (median sample = 11) and a total of 303 participants.
Results: The main multilevel meta-analysis model including all effects sizes (278 across 50 clusters [median = 4, range = 1 to 18 effects per cluster) revealed a trivial point estimate with high precision for the interval estimate (-0.02 [95%CIs = -0.14 to 0.09]), yet with substantial heterogeneity (Q(277) = 642.3, p < 0.01), I2 = 67.4%). Subgroup and meta-regression analyses showed that NLMF effects were not moderated by study design (between vs. within-participant), homologous vs. heterologous effects, upper or lower body effects, participant training status, sex, age, the time of post-fatigue protocol measurement, or the severity of the fatigue protocol. However, there did appear to be an effect of type of outcome measure where both strength (0.11 [95%CIs = 0.01 to 0.21]) and power outcomes had trivial effects (-0.01 [95%CIs = -0.24 to 0.22]), whereas endurance outcomes showed moderate albeit imprecise effects (-0.54 [95%CIs = -0.95 to -0.14]).
Conclusions: Overall, the findings do not support the existence of a general NLMF effect; however, when examining specific types of performance outcomes there may be an effect specifically upon endurance-based outcomes (i.e., time to task failure). However, there are relatively fewer studies that have examined endurance effects or mechanisms explaining this possible effect, in addition to fewer studies including women or younger and older participants, and considering causal effects of prior training history through the use of longitudinal intervention study designs. Thus, it seems pertinent that future research on NLMF effects should be redirected towards these still relatively unexplored areas.
... It is recognised that with long-term sport practice, the type of training shapes the neuromuscular profile of an athlete's lower limb. Especially, power-type athletes showed greater mechanical twitch of plantar flexors (Casabona, Polizzi, & Perciavalle, 1990;Grosprêtre, Gimenez, & Martin, 2018;Lattier, Millet, Maffiuletti, Babault, & Lepers, 2003;Maffiuletti et al., 2001). However, while neuromuscular parameters have been well documented, less is known about the modulation of corticospinal networks with the practice of a power-type activity. ...
It is recognized that power-sport practices have a particular effect on lower-limb neuromuscular parameters. Less is known about corticospinal network adaptation, however, or whether these adaptations are specific to the lower limb. In the present study, the corticospinal and spinal excitabilities of upper and lower limbs have been examined in a group of untrained participants (UT, n = 10) and compared to those of a group of well-trained athletes practicing parkour (PK, n = 10). This activity, consisting of overcoming obstacles offered by the urban environment, was chosen as a model of power activity. The motor evoked potentials (MEPs) induced by transcranial magnetic stimulations and H-reflexes and maximal M-waves evoked by peripheral nerve stimulations were elicited in both upper- (flexor carpi radialis [FCR]) and lower-limb muscles (soleus [SOL] and gastrocnemius medialis [GM]). The results tended toward an overall greater corticospinal excitability in PK than in UT (as evidenced by greater MEP/Mmax ratio) and lower spinal excitability (lower Hmax/Mmax). H/MMAX ratio was lower for PK (0.32) than for UT (0.41) in SOL (p = 0.02), while MEP/MMAX was greater for PK than for UT in FCR (PK: 0.12; UT: 0.06; P = 0.04) and in GM (PK: 0.05, UT: 0.03, P = 0.02). In both limbs, the decrease of spinal excitability induced by parkour practice was counterbalanced by an increase in cortical excitability. Finally, the present study indicates that such long-term power practice leads to similar corticospinal plasticity in upper and lower limbs, explained by the similar solicitation of those muscles.
... For example, Fielding et al. (2002) found that a ERT program significantly improved peak power, and was equally efficient at increasing muscle strength compared to TRT. In addition to prior training studies, previous authors have assessed neuromuscular differences between individuals with different training backgrounds (Häkkinen and Keskinen 1989;Lattier et al. 2003). Recently, a trend in ERT has incorporated workouts consisting of power movements in combination with other varied functional movements performed at high intensity or to failure (Bergeron et al. 2011;Hak et al. 2013;Smith et al. 2013). ...
Purpose:
To compare maximal and rapid force characteristics, as well as fatigability, between traditional (TRT) and explosive (ERT) resistance-trained men.
Methods:
Fourteen TRT (mean age = 25 years) and twelve ERT (mean age = 22 years) men performed rapid maximal contractions followed by an isokinetic fatigue protocol consisting of 50 maximal knee extension (KE) and flexions (KF) at a moderate speed (180° s-¹). Baseline measures included: isokinetic peak torque (PT), isometric rate of torque development (RTD0-50), peak acceleration (ACCmax), and peak velocity (Vmax). Changes in torque with fatigue were used to calculate a fatigue index (FI%).
Results:
The ERT group (M ± SD; 1199.05 ± 404.12) displayed a significantly higher isometric RTD0-50 (p = 0.049) during KE than the TRT group (931.73 ± 244.75). No other significant differences in the dependent variables (PT, FI%, ACCmax, Vmax; all p ≥ 0.05) were observed between groups (TRT vs. ERT) for either of the muscle groups (KE and KF).
Conclusions:
The results of the present study indicated that only knee extension RTD was able to discriminate between the two groups. These findings suggest that rapid force production may be more sensitive at distinguishing training-specific muscular adaptations than peak acceleration or velocity.
... Despite these challenges, intrinsic muscle contractile mechanics are key mediators of performance (Costill, Fink, & Pollock, 1975;García-García et al., 2015;Lattier, Millet, Maffiuletti, Babault, & Lepers, 2003;Loturco et al., 2015). Any unloaded (i.e. ...
... Enhanced thermoregulatory efficiency achieved via HA may protect self-paced exercise performance in the heat, but how such strategies can influence neuromuscular mechanisms, including central and peripheral contributions to performance outcomes remain unknown. This is notable considering the specificity of neuromuscular adaptations to exercise prescription (Häkkinen et al., 2003) and the relationships between maximal voluntary contraction (MVC) and training status (Lattier et al., 2003). ...
... These changes in MVC can be readily explained by both morphological and neural adaptations to strength training (Folland and Williams, 2007) carried out by elite rugby league players in our ST group. The absence of difference in MVC between CO and ED agreed with Chã et al. (2010) but contrasts with Dal Maso et al. (2012) and Lattier et al. (2003) who reported similar MVC in endurance-trained and strength-or power-trained individuals. This apparent discrepancy may be explained by between-studies differences in the sport disciplines practiced by the participants. ...
The synchronous activation of the muscles involved in force production is crucial for the neuromuscular performance, but the underlying mechanisms remain to be fully elucidated. Our aim was thus to contribute to understand the mechanisms involved in the synergistic activation of agonist muscles. Through wavelet-based time-frequency analysis, this study investigated the modulation of ’beta’ intermuscular interactions (IM) during maximum isometric knee extensions performed before and after repetitive submaximal fatiguing contractions. Three groups of participants were included: 9 untrained subjects (control group, CO), 10 elite rugby league players (strength-trained group, ST) and 7 trail runners (endurance-trained group, ED), engaged for 5+ years in intense strength and endurance training, respectively. Before fatigue, CO showed higher IM when compared to ED, and a trend to higher IM when compared to ST. Following fatiguing contractions, all groups showed a decline in neuromuscular performance concomitant with a change (decline) in IM values for CO only. No differences were found between ST and ED regarding to IM either before or after fatiguing contractions. These findings suggested both a form of optimization of intermuscular coupling in trained individuals and the functional importance of intermuscular coupling as a mechanism responsible for the maintenance of the neuromuscular performance.
... Furthermore, although data of the cited studies indicate that the H-reflex at rest and during weak voluntary contractions is increased in response to short-term endurance training (Perot et al., 1991;Vila-Cha et al., 2012b), nothing is known about H-reflex modulation during iMVC. Even though it has been shown that V-wave responses of SOL and cortical voluntary activation of the knee extensors were unchanged following short-term endurance training (Vila-Cha et al., 2012b;Zghal et al., 2014), H-reflex modulation during iMVC is of particular interest because it has been revealed that endurance athletes possess a greater iMVC strength compared to sedentary subjects (Lattier et al., 2003). Therefore, it is not unlikely that endurance training alters the contribution of the Ia afferent pathway to the muscle activity during iMVC. ...
Previously published studies on the effect of short-term endurance training on neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after 8 weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100, 100–200 ms) and iMVC of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that cycling endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance.
... Due to the continuous demand of producing quick muscle contractions it is no surprise that power athletes show superior performance in speed and power tests (e.g. drop & squat jump) compared to their endurance counterparts [26,27]. The current study investigated thirty-two healthy track-and-field athletes from regional to international level after obtaining written informed consent. ...
In athletics, motor performance is determined by different abilities such as technique, endurance, strength and speed. Based on animal studies, motor speed is thought to be encoded in the basal ganglia, sensorimotor cortex and the cerebellum. The question arises whether there is a unique structural feature in the human brain, which allows "power athletes" to perform a simple foot movement significantly faster than "endurance athletes". We acquired structural and functional brain imaging data from 32 track-and-field athletes. The study comprised of 16 "power athletes" requiring high speed foot movements (sprinters, jumpers, throwers) and 16 endurance athletes (distance runners) which in contrast do not require as high speed foot movements. Functional magnetic resonance imaging (fMRI) was used to identify speed specific regions of interest in the brain during fast and slow foot movements. Anatomical MRI scans were performed to assess structural grey matter volume differences between athletes groups (voxel based morphometry). We tested maximum movement velocity of plantarflexion (PF-Vmax) and acquired electromyographical activity of the lateral and medial gastrocnemius muscle. Behaviourally, a significant difference between the two groups of athletes was noted in PF-Vmax and fMRI indicates that fast plantarflexions are accompanied by increased activity in the cerebellar anterior lobe. The same region indicates increased grey matter volume for the power athletes compared to the endurance counterparts. Our results suggest that speed-specific neuro-functional and -structural differences exist between power and endurance athletes in the peripheral and central nervous system.
... Stiffness alterations negatively impact force transmission and may yield to an increase of the electromechanical delay [29][30][31]. The vertical jump performance being correlated to both the rate of force development [32] and stiffness [33], MTU stiffness decrease may lower the vertical jump height. This MTU stiffness reduction might also negatively impact the maximal sprint speed [34] and maximal strength production capacity [35]. ...
Objectifs
Cette étude explorait les effets aigus d’étirements statiques, isolés ou combinés avec des exercices pliométriques, sur la performance en force, détente verticale et sprint.
Sujets et méthode
Lors de trois sessions et après un échauffement standardisé, 15 participants ont réalisé de manière aléatoire des exercices d’étirements statiques seuls, étirements statiques combinés avec des exercices pliométriques et pas d’étirements. La durée totale des étirements était de 20 secondes par groupe musculaire (quadriceps, ischios-jambiers et triceps sural). Les tests ont permis d’évaluer la force maximale du quadriceps, la hauteur des sauts avec contre mouvement et des sprints de 15 m.
Résultats
Quelle que soit la condition, la force maximale et les sprints n’ont pas été modifiés tandis que la hauteur maximale de saut a diminué significativement (p < 0,05). Nous avons conclu que des étirements statiques, isolés ou combinés avec des exercices pliométriques, même avec de courtes durées, n’étaient pas efficaces pour améliorer la force, la détente verticale et la vitesse de sprints et doivent par conséquent être exclus des sessions d’échauffement.
... Our task was also kinematically isometric and thus results may not be directly applied to dynamic conditions. Finally, we did not specify physical activity type, experience level or frequencies in our subject exclusion criteria, even though knee muscle activation varies as a function of physical activity level (da Fonseca et al., 2006) and type (Lattier et al., 2003). This may explain our high between subject variation of X EMG levels. ...
Previous investigations have identified the roles of knee joint muscles in supporting external loads during non-weight-bearing tasks and found these to depend on moment arm orientation (MAO). However, during weight-bearing tasks ground reaction forces (GRF) are transferred up through the knee, subjecting it to large multi-directional forces and stability is dependent on articular geometry, loading, and muscle activation. The purpose of this study was to investigate activation strategies used by healthy individuals to generate and support highly controlled GRF during weight-bearing.
... In the present study, we selected elite sprint cyclists well familiarized with WT, and we hypothesized that in these subjects the effects of NaHCO 32 ingestion over WT should be more significant than those published previously in sedentary subjects. It is known that sprinters have an increased ability to activate high-threshold motor units during maximal voluntary contractions (16) and a greater percentage of type II fibers in their muscles than endurance trained or untrained subjects (9). Fast-twitch fibers are characterized by a greater intramuscular acidosis during their activation (nearly fourfold difference in the maximum mechanical power output and the ATP hydrolysis rate) than slow-twitch fibers (44). ...
The objective of this study was to examine the effect of sodium bicarbonate (NaHCO3-) ingestion on performance and perceptual responses in a laboratory-simulated bicycle motocross (BMX) qualification series. Nine elite BMX riders volunteered to participate in this study. After familiarization, subjects undertook two trials involving repeated sprints (3 x Wingate tests [WTs] separated by 30 minutes of recovery; WT1, WT2, WT3). Ninety minutes before each trial, subjects ingested either NaHCO3- or placebo in a counterbalanced, randomly assigned, double-blind manner. Each trial was separated by 4 days. Performance variables of peak power, mean power, time to peak power, and fatigue index were calculated for each sprint. Ratings of perceived exertion were obtained after each sprint, and ratings of perceived readiness were obtained before each sprint. No significant differences were observed in performance variables between successive sprints or between trials. For the NaHCO3- trial, peak blood lactate during recovery was greater after WT2 (p < 0.05) and tended to be greater after WT3 (p = 0.07), and ratings of perceived exertion were not influenced. However, improved ratings of perceived readiness were observed before WT2 and WT3 (p < 0.05). In conclusion, NaHCO3- ingestion had no effect on performance and RPE during a series of three WT simulating a BMX qualification series, possibly because of the short duration of each effort and the long recovery time used between the three WTs. On the contrary, NaHCO3- ingestion improved perceived readiness before each WT.
... This result contradicts the findings of Kujala and others (1994), who concluded that improved performance in the vertical jump is associated with higher levels of physical exercise, especially that which involves cross training in which there is a mixture of intensity, duration, and frequency. On the other hand, previous studies have demonstrated that specific power training is necessary to improve vertical jump performance (Lattier, Millet, Maffiuletti, Babault, & Lepers, 2003). ...
The objective of the present study was to evaluate the practice of regular physical exercise, the anthropometrical and physiological characteristics, and the dietary habits of a group of female nursing students (n=46) and of a control group of female students from other disciplines (n=58) attending the University of the Basque Country. To this end, diets and leisure-time physical exercise were analyzed and the following variables were measured: body mass index, body composition, blood pressure, maximal oxygen consumption (VO2 max), and explosive muscle strength. Results show that the percentage of sedentary students was higher among first-year nursing students (50%) than among other matched students (43.6%). Regular physical exercise in nursing students was found to be positively correlated with higher absolute (p < .01) and relative VO2 max (p < 0.05) and with lower diastolic blood pressure (p < 0.05). Analysis of the diets of the nursing students showed that their energetic intake was deficient and was very low in carbohydrates and very high in fat and protein. Statistically significant differences between the two groups in anthropometric indices were not observed. The competence to provide adequate nutritional and preventive physical exercise recommendations was higher among active final-year nursing students than among sedentary final-year nursing students. Overall, the results of the present study highlight the need for a greater emphasis on the benefits of regular physical exercise and an adequate nutritional education early in the nursing educational program to encourage students to adopt healthier behaviors and to provide more effective preventive physical exercise and nutritional counseling for their future patients.
... Increased ability to activate the high threshold motor units during the conditioning contraction involving type II muscle fibers should increase PAP, because type II muscle fibers show the greatest potentiation . Lattier et al. (2003) demonstrated a significantly greater voluntary activation of the KE muscles in elite male PT athletes than UT men; however, when compared with elite ET athletes, the differences in voluntary activation were insignificant. As an indicator of the ratio between electrically evoked twitch and voluntary contraction, we calculated isometric twitch Pt:MVC torque ratio, which was significantly lower in female PT athletes compared with the UT women and ET athletes. ...
This study compared postactivation potentiation (PAP) in knee extensor muscles after a 10 s conditioning isometric maximal voluntary contraction (MVC) in female power- (PT, n=12) and endurance-trained (ET, n=12) athletes, and untrained (UT, n=12) women aged 20-24 years. Isometric twitch characteristics of the knee extensor muscles were assessed in pre-MVC condition and during 15 min post-MVC period using supramaximal electrical stimulation of the femoral nerve by rectangular pulses of 1 ms duration. A significant (P<0.05) potentiation of twitch peak torque (Pt, 30-51% in different groups), maximal rates of torque development (50-125%) and relaxation (76-124%) occurred immediately (2 s) post-MVC. PAP declined sharply at 1-3 min of recovery, whereas a significant potentiation of twitch Pt was still present for ET athletes at 1 min, and for UT women and PT athletes at 5 min of recovery, respectively. There were no significant (P>0.05) changes in twitch contraction and half-relaxation times after a 10 s conditioning MVC. We concluded that PAP in knee extensor muscles is enhanced in PT but not in ET female athletes. The magnitude of PAP was greater when measured immediately after the conditioning MVC and its decline was slower in PT compared with ET athletes. Immediately post-MVC, twitch speed-related characteristics were potentiated to a greater extent than twitch Pt. The time-course of isometric twitch was not significantly altered by conditioning MVC.
Background
Neuromuscular function is considered as a determinant factor of endurance performance during adulthood. However, whether endurance training triggers further neuromuscular adaptations exceeding those of growth and maturation alone over the rapid adolescent growth period is yet to be determined.
Objective
The present study investigated the concurrent role of growth, maturation, and endurance training on neuromuscular function through a 9‐month training period in adolescent triathletes.
Methods
Thirty‐eight 13‐ to 15‐year‐old males (23 triathletes [~6 h/week endurance training] and 15 untrained [<2 h/week endurance activity]) were evaluated before and after a 9‐month triathlon training season. Maximal oxygen uptake (V̇O2max) and power at V̇O2max were assessed during incremental cycling. Knee extensor maximal voluntary isometric contraction torque (MVCISO) was measured and the voluntary activation level (VAL) was determined using the twitch interpolation technique. Knee extensor doublet peak torque (T100Hz) and normalized vastus lateralis (VL) electromyographic activity (EMG/M‐wave) were also determined. VL and rectus femoris (RF) muscle architecture was assessed using ultrasonography.
Results
Absolute V̇O2max increased similarly in both groups but power at V̇O2max only significantly increased in triathletes (+13.8%). MVCISO (+14.4%), VL (+4.4%), and RF (+15.8%) muscle thicknesses and RF pennation angle (+22.1%) increased over the 9‐month period in both groups similarly (p < 0.01), although no changes were observed in T100Hz, VAL, or VL EMG/M‐wave. No changes were detected in any neuromuscular variables, except for coactivation.
Conclusion
Endurance training did not induce detectible, additional neuromuscular adaptations. However, the training‐specific cycling power improvement in triathletes may reflect continued skill enhancement over the training period.
The current study involved the completion of two distinct experiments. Experiment 1 analyzed the inter-day reliability of tensiomyography (TMG) muscle mechanical properties based on the amplitude of the muscle belly radial deformation, the time it takes to occur, and its velocity under maximal and submaximal stimuli, in the muscles rectus femoris, biceps femoris, and gastrocnemius lateralis, from 20 male sport students. Experiment 2 investigated whether changes in maximal voluntary isometric contraction (MVIC) could be predicted based on changes in TMG properties following 24 h after different squat training protocols (MS = multiple sets; DS = drop sets; EO = eccentric overload; FW = flywheel; PL = plyometrics) executed by 14 male strength trained athletes. Maximal electrical stimulation exhibited higher level of reliability. In most of the cases, TMG properties Tc, Td, Dm, V10, and V90 showed ICC scores >.8 and CV <10%. Simple linear regression analysis revealed that changes in Dm, V10, and V90 correlated with changes in MVIC following EO at r = .705, .699, and .695, respectively. TMG is a reliable method to assess muscle mechanical properties particularly within maximal stimuli and can be used for prediction of changes in MVIC following heavy eccentric strength exercises.
The preferential training of dominant over non-dominant limbs is usually associated with an increase in muscle function. The aim of this study was to examine the effect of chronic high jump training on lateral dominance in knee muscle function. Nine national high jumpers (5 females, 4 males) and fourteen controls performed maximal knee flexions and extensions (0° to 180°.s-1) with dominant and non-dominant legs. Male high jumpers were stronger (p < 0.001) but more asymmetric than controls during maximal isometric knee extension (+17% for the dominant leg, p < 0.01) in contrast with maximal concentric knee extensions (-5% to +2%, p > 0.05). Additionally, levels in agonist and antagonist EMG activity during knee extensions were similar across groups. These results suggest that neither neural activation or typology were responsible for the laterality observed in male high jumpers. According to current knowledge on the effects of plyometric training and functional characteristics of power-athletes, we hypothesized that this muscle- and velocity-specific lateral dominance in competitive male high jumpers was related to differences in terms of muscle volume and/or muscle stiffness. Further studies are needed to examine these assumptions with suitable techniques over a larger sample of competitive high jumpers.
The purpose of the present work is to determine the influence of the muscular properties of the lower limbs on the locomotor pattern. The first studies (studies n°l and n°2) analyse the relationship between the strength capacity of the lower extremity muscles and the choice of a particular locomotor pattern during cycling. Our results indicate that, on healthy subject, the locomotor pattern is not affected by the muscular characteristics. On the other hand, the muscular properties modify the synergy of the muscle coordination and the criteria of energy and neuromusoular efficiency during locomotion. The three following studies (3, 4 and 4bis) aim to characterize the effects of various muscular alterations on locomotion. Two methods are used to generate these alterations. The first consists to generate a muscular fatigue from two types of repeated lower limbs contractions (concentric vs. eccentric) (Study 3). The second method is comparative, and aims to analyze the effects of a fatiguing exercise on the locomotion in two populations with different muscular properties (young vs. elderly adults) (Studies 4 and 4bis). The results of the study 3 show, on the one hand, that muscular alterations are directly dependent on the type of contraction and, on the other hand, that these alterations specifically modify the locomotor pattern. The two last studies produce two original results, The first result indicates that the alteration of the muscular properties after a fatiguing exercise is potentiated when the subjects have a preliminary muscular insufficiency. The second result shows that, whatever the characteristics of the muscular function, the modification of the locomotor pattern after a fatiguing exercise is always the same. However, this adaptation is accompanied by a reorganization of the muscular cooperation specific to each population. The whole of this experimental work suggests that the muscular properties of the lower limbs, altered or not, do not influence the kinematics of the locomotor pattern. However, they could determine a particular organization of the muscular synergies to produce the movement
Non-local muscle fatigue (NLMF) is characterized by muscle performance impairments in a contralateral or remote non-exercised muscle(s) following a fatiguing protocol of a different muscle group(s). This topic is of interest as it affords insights into physiological determinants of muscle fatigue and may provide practical applications concerning the order of exercises in training and rehabilitation programs.
A literature review was conducted using Web of Science, PubMed, and Google Scholar databases to evaluate the NLMF effects and possible underlying mechanisms. Overall, 35 studies with 58 outcome measures that met the inclusion criteria were identified.
The literature is conflicting with approximately half of the studies reporting NLMF effects (32 of 58 measurements). However, on closer examination 76 % of outcome measures of the lower limbs reported NLMF effects (23 of 30 measurements) compared to only 32 % in the upper body (9 of 28 measurements). Thus, it appears that NLMF effects may be muscle group dependent. Also, tests that involve prolonged or repetitive contractions provide clearer evidence of NLMF. Other variables potentially influencing the size of the NLMF effect include the fatigued muscle groups, the protocols used to elicit the fatigue, gender and training background of participants.
While the NLMF literature is conflicting, certain variables appear to affect NLMF responses which can account for some of the discrepancies. Furthermore, the NLMF effects may be attributed to four different but interconnected pathways: neurological, biochemical, biomechanical and psychological.
Muscular coactivation is fundamental in joint protection and stabilization during voluntary contractions and plays an important role in movement control. Numerous studies have already highlighted the contribution of supraspinal and spinal mechanisms in the regulation of muscular coactivation but the involvement of the primary motor cortex (M1) is still unclear. We studied the modulation of cortical oscillations and cortico-muscular interactions during isometric contractions in athletes with different levels of muscular coactivation as a consequence of their training orientation (strength (ST) vs. endurance (ED). We found that in ST, reduced muscular coactivation was associated with greater M1 activation, which could be explained by the control of a greater number of muscles, including antagonist muscles. Using a novel method to analyze cortico-muscular interactions, we found that M1 is directly involved in the control of antagonist muscles in all participants. However, the magnitude of cortico-muscular interactions with antagonist muscles was lower than in agonist muscles, which could be explained by a greater involvement of spinal mechanisms in the regulation of muscular coactivation. The estimation of agonist and antagonist muscle group moments opens the perspective to investigate the cerebral correlates of the modulation of muscular torque. Our results obtained through an approach combining biomechanics and neurosciences highlighted the involvement of M1 in the regulation of the muscular coactivation during isometric voluntary contractions.
Strength loss and enhanced neuromuscular fatigue are major contributing factors of impaired functional capacities, exercise tolerance and prognosis in patients with various chronic diseases. These alterations can rely on primary deficiencies of neuromuscular function and/or secondary impairments caused by decreased spontaneous physical activity promoted by a chronic disease. Consequently, muscle weakness and enhanced fatigability are frequently reported symptoms in neuromuscular (inherited or noninherited myopathies/neuropathies), cardiovascular (chronic cardiac failure) and respiratory diseases (chronic obstructive pulmonary disease (COPD)) and idiopathic painful syndromes associated with alteration of nociception (fibromyalgia syndrome). The development of reliable and well-tolerated evaluations of muscle strength, endurance and fatigue is of major interest to better understand the physiopathology of the diseases and to provide relevant outcomes for observational or interventional studies. Artificially muscular electrical stimulation has been recognized as a valuable tool for noninvasive assessments of neuromuscular function at rest and during exercise in human. Recently, magnetic stimulation showed interesting skills to assess both peripheral and respiratory muscles in the clinical field. During this work, we developed tools to assess muscle strength, endurance and fatigue using magnetic neurostimulation and exercise protocols usable in patients. We studied its ability to detect differences related to sex, age and training status. Then we used these procedures in neuromuscular diseases and fibromyalgia syndrome. In COPD patients, we assessed respiratory and locomotor muscle fatigue and studied how these phenomena impact on exercise response and perceived symptoms. In these patients, we also assessed the combined effects of locomotor and respiratory muscle training on these parameters.
Strength loss and enhanced neuromuscular fatigability are major contributing factors of decreased functional capacities, reduction of exercise capacity and impaired prognosis in patients with chronic diseases. These alterations can rely upon primary impairments of neuromuscular function and/or secondary impairments partly caused for instance, by a decreased spontaneous physical activity promoted by a chronic disease. Consequently, muscle weakness and enhanced fatigability are frequently reported symptoms in neuromuscular diseases (e.g. inherited or noninherited myopathies and neuropathies), cardiovascular diseases (e.g. chronic cardiac failure), respiratory diseases (e.g. chronic obstructive pulmonary disease) and chronic painful syndromes.
Hence the development of reliable and well-tolerated evaluation of muscle function is critical to understand the physiopathology of the diseases and to provide relevant outcomes for observational and interventional studies. Artificial stimulation has been recognized as a valuable tool for noninvasive assessments of neuromuscular function at rest and during exercise. In particular, magnetic stimulation showed interesting skills to assess both peripheral and respiratory muscles in patients.
During this work, we developed tools to assess muscle strength, endurance and fatigue with the support of magnetic neurostimulation and by using exercise protocols applicable in patients. We studied the reliability of these tools in healthy subjects and patients and their abilities to detect differences related to sex, age and training status. Then we used these procedures in neuromuscular diseases and chronic painful syndromes to address the impact of alterations of neuromuscular function on symptoms, exercise capacity and quality of life. In COPD patients, we assessed exercise-induced respiratory and locomotor muscle fatigue, their relationship and studied their impact on exercise response and limiting perceived symptoms. By using these tools , we also investigated the effects of exercise-based therapeutic intervention including locomotor and respiratory muscle training in these populations.
Electromechanical delay (EMD) and rate of force development (RFD) are determinants of explosive neuromuscular performance. We may expect a contrast in EMD and RFD between explosive power athletes, who have a demonstrable ability for explosive contractions, and untrained individuals. However, comparison and the neuromuscular mechanisms for any differences have not been studied.
The neuromuscular performance of explosive power athletes (n = 9) and untrained controls (n = 10) was assessed during a series of twitch, tetanic, explosive, and maximum voluntary isometric knee extensions. Knee extension force and EMG of the superficial quadriceps were measured in three 50-ms time windows from their onset and were normalized to strength and maximal M-wave (Mmax), respectively. Involuntary and voluntary EMD were determined from twitch and explosive voluntary contractions, respectively, and were similar for both groups.
The athletes were 28% stronger, and their absolute RFD in the first 50 ms was twofold that of controls. Athletes had greater normalized RFD (4.86 ± 1.46 vs 2.81 ± 1.20 MVC·s(-1)) and neural activation (mean quadriceps, 0.26 ± 0.07 vs 0.15 ± 0.06 Mmax) during the first 50 ms of explosive voluntary contractions. Surprisingly, the controls had a greater normalized RFD in the second 50 ms (6.68 ± 0.92 vs 7.93 ± 1.11 MVC·s-1) and a greater change in EMG preceding this period. However, there were no differences in the twitch response or normalized tetanic RFD between groups.
The differences in voluntary normalized RFD between athletes and controls were explained by agonist muscle neural activation and not by the similar intrinsic contractile properties of the groups.
The purpose of this study was to examine the physiological and biomechanical changes occurring in a subject after running 8,500 km in 161 days (i.e. 52.8 km daily). Three weeks before, 3 weeks after (POST) and 5 months after (POST+5) running from Paris to Beijing, energy cost of running (Cr), knee flexor and extensor isokinetic strength and biomechanical parameters (using a treadmill dynamometer) at different velocities were assessed in an experienced ultra-runner. At POST, there was a tendency toward a 'smoother' running pattern, as shown by (a) a higher stride frequency and duty factor, and a reduced aerial time without a change in contact time, (b) a lower maximal vertical force and loading rate at impact and (c) a decrease in both potential and kinetic energy changes at each step. This was associated with a detrimental effect on Cr (+6.2%) and a loss of strength at all angular velocities for both knee flexors and extensors. At POST+5, the subject returned to his original running patterns at low but not at high speeds and maximal strength remained reduced at low angular velocities (i.e. at high levels of force). It is suggested that the running pattern changes observed in the present study were a strategy adopted by the subject to reduce the deleterious effects of long distance running. However, the running pattern changes could partly be linked to the decrease in maximal strength.
Four male subjects aged 23-34 years were studied during 60 days of unilateral strength training and 40 days of detraining. Training was carried out four times a week and consisted of six series of ten maximal isokinetic knee extensions at an angular velocity of 2.09 rad.s-1. At the start and at every 20th day of training and detraining, isometric maximal voluntary contraction (MVC), integrated electromyographic activity (iEMG) and quadriceps muscle cross-sectional area (CSA) assessed at seven fractions of femur length (Lf), by nuclear magnetic resonance imaging, were measured on both trained (T) and untrained (UT) legs. Isokinetic torques at 30 degrees before full knee extension were measured before and at the end of training at: 0, 1.05, 2.09, 3.14, 4.19, 5.24 rad.s-1. After 60 days T leg CSA had increased by 8.5% +/- 1.4% (mean +/- SEM, n = 4, p less than 0.001), iEMG by 42.4% +/- 16.5% (p less than 0.01) and MVC by 20.8% +/- 5.4% (p less than 0.01). Changes during detraining had a similar time course to those of training. No changes in UT leg CSA were observed while iEMG and MVC increased by 24.8% +/- 10% (N.S.) and 8.7% +/- 4.3% (N.S.), respectively. The increase in quadriceps muscle CSA was maximal at 2/10 Lf (12.0% +/- 1.5%, p less than 0.01) and minimal, proximally to the knee, at 8/10 Lf (3.5% +/- 1.2%, N.S.). Preferential hypertrophy of the vastus medialis and intermedius muscles compared to those of the rectus femoris and lateralis muscles was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
This study compared twitch contractile properties of plantar flexor muscles among three groups of 12 subjects each: endurance and power trained athletes and untrained subjects. The posterior tibial nerve was stimulated by supramaximal square wave pulses of 1-ms duration. Power trained athletes had higher twitch maximal force, maximal rates of force development and relaxation and also maximal voluntary contraction (MVC) force. The trained subjects had a smaller twitch maximal force: MVC force ratio and shorter twitch contraction and half-relaxation times than the untrained subjects with no significant differences between the two groups. Thus, the short time for evoked twitches in the athletes compared to the untrained subjects would seem unrelated to the type of training. It is concluded that power training induces a more evident increase of muscle force-generating capacity and speed of contraction and relaxation than endurance training.
The purpose of the study was to compare the contractile properties determined from an electrically stimulated twitch with histochemically determined fibre type parameters of the human triceps surae. Muscle samples were obtained from the medial head of the gastrocnemius of ten male athletes. Ages ranged from 20 to 29 years. Muscle samples from the belly of the medial gastrocnemius muscle were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase to classify the fibres as either slow twitch (ST) or fast twitch (FT) and to determine fibre areas. Surface electrical stimulation was used to determine muscle twitch parameters. The contractile variables of the muscle twitch were latency (L), time to peak force (TPF), peak force (PF), half-contraction time (1/2 CT) and half-relaxation time (1/2 RT). Backward elimination procedures for dependent variables were used to determine which contractile properties best represented the histochemical profile of the muscles. Prediction formulas were developed for FT and ST percentages (R2=0·98, p<0·001), relative area percentage (R2=0·87, p<0·001), and ST area (R2=0·85, p<0·01). It was concluded that the use of the electrotensiometer (ETM) protocol was a valid testing procedure when studying physiological relationships of histochemical properties in intact human skeletal muscle.
Loss of cells from the motor system occurs during the normal aging process, leading to reduction in the complement of motor neurons and muscle fibers. The latter age-related decrease in muscle mass has been termed “sarcopenia” and is often combined with the detrimental effects of a sedentary lifestyle in older adults, leading to a significant reduction in reserve capacity of the neuromuscular system, which is the primary subject of this review. Clear evidence of this aging effect is seen when voluntary or stimulated muscle strength is compared across the adult lifespan, with a steady decline of ∼1–2% per year occurring after the sixth decade. Interestingly, when compared with isometric contractions, the effect of aging is more pronounced for concentric movements and less for eccentric movements (i.e., muscle shortening versus lengthening). This phenomenon appears to be linked to the stiffer muscle structures and prolonged myosin crossbridge cycles of aged muscles. It is encouraging that the capability of physiological adaptations in the motor pathways remains into very old age — when an appropriate exercise stimulus is given — and long-term prevention strategies are advocated to avoid excessive physical impairments and activity restrictions in this age group. © 2002 John Wiley & Sons, Inc. Muscle Nerve 25: 17–25, 2002
Neural, mechanical and muscle factors influence muscle force production. This study was, therefore, designed to compare possible differences in the function of the neuromuscular system among differently adapted subjects. A group of 11 power-trained athletes and 10 endurance-trained athletes volunteered as subjects for this study. Maximal voluntary isometric force and the rate of force production of the knee extensor and the plantar flexor muscles were measured. In addition, basic reflex function was measured in the two experimental conditions. The power athletes produced higher voluntary forces (P<0.01-0.001) with higher rates for force production (P<0.001) by both muscle groups measured. Unexpectedly, however, no differences were noticed in the electromyogram time curves between the groups. During reflex activity, the endurance group demonstrated higher sensitivity to the mechanical stimuli, i.e. the higher reflex amplitude caused a higher rate of reflex force development, and the reflex amplitude correlated with the averaged angular velocity. The differences in the isometric conditions could be explained by obviously different muscle fibre distribution, by different amounts of muscle mass, by possible differences in the force transmission from individual myofibrils to the skeletal muscle and by specificity of training. In addition, differences in nervous system structure and muscle spindle properties could explain the observed differences in reflex activity between the two groups.
The effects of an 8 weeks period of systematic progressive strength training on the EMG activity of the leg extensor muscles (vastus lateralis and rectus femoris) were investigated in 8 healthy male subjects (22-31 yrs). After training there were indications (n.s.) of a decline in integrated EMG (IEMG) during maximal isometric knee extension as well as in the IEMG vs isometric force relationship. The averaged motor unit potential (AMUP) did not demonstrate any significant changes due to the strength training regimen. In conformity with earlier findings no or only minor alterations were observed in anthropometrics, muscle enzyme activities and fibre composition. The fibre area ratio indicated a specific effect of the training stimuli on the fast twitch muscle fibres. Thus, EMG-analyses, as employed in the present study, did not provide any conclusive additional explanation as to the mechanisms behind the well established gains in muscle strength performance induced by the applied strength training program.
To elucidate the changes in neuro-muscular function during strength training and detraining, five male subjects underwent progressive isotonic strength training of their calf muscles three times a week for 8 weeks with additional detraining for the same periods. Electrically evoked twitch contractions were induced in the triceps surae muscles of each subject every 4 weeks during the training and detraining periods. At the same time, maximal voluntary isometric contractions (MVC) and the maximal girth of the calf (MGC) were measured. During the training period, MVC increased significantly from 98.4 to 129.6 Nm (31.7%, P less than 0.01) for the first 4 weeks of training but MGC showed little increase. Neither of the changes correlated with each other. Twitch contraction parameters, i.e. maximal twitch torque (Pt), maximal rate of torque development (max dT/dt) and rate of relaxation (relax dT/dt) showed no statistical change. During detraining, on the contrary, a large and significant increase (22.5%, P less than 0.01) was observed in max dT/dt without any changes in Pt and relax dT/dt. The MVC/Pt showed both significant increases during training and decreases during detraining. Our data suggest that short term strength training as employed in the present study does not induce changes in the contractile properties of the muscle during training, but may significantly affect the rate of force development during the subsequent detraining period, indicating the possible existence of complex post-training muscle adaptation.
Seven male elite strength-trained athletes (SA) from different weight categories, six elite sprinters (SPA) and seven elite endurance-trained athletes (EA) volunteered as subjects for examination of their muscle cross-sectional area (CSA), maximal voluntary isometric force, force-time and relaxation-time characteristics of the leg extensor muscles. The SA group demonstrated slightly greater CSA and maximal absolute strength than the SPA group, while the EA group demonstrated the smallest values both in CSA and especially in maximal strength (p less than 0.05). When the maximal forces were related to CSA of the muscles, the mean value for the SA group of 60.8 +/- 10.0 N.cm-2 remained slightly greater than that recorded in the SPA group 55.0 +/- 3.1 N.cm-2 and significantly greater (p less than 0.05) than that recorded in the EA group 49.3 +/- 4.0 N.cm-2. The mean value in the SPA was also significantly greater (p less than 0.05) than that of the EA group. The isometric force-time curves differed between the groups (p less than 0.05-0.01) so that the times taken to produce the same absolute force were the shortest in the SPA group and the longest in the EA group. With force expressed as a percentage of the maximum, the force-time curves showed that the SPA group demonstrated still shorter times to a given value (p less than 0.05), especially at the lower force levels, than the other two groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Strength performance depends not only on the quantity and quality of the involved muscles, but also upon the ability of the nervous system to appropriately activate the muscles. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime movers in specific movements and to better coordinate the activation of all relevant muscles, thereby effecting a greater net force in the intended direction of movement. The evidence indicating neural adaptation is reviewed. Electromyographic studies have provided the most direct evidence. They have shown that increases in peak force and rate of force development are associated with increased activation of prime mover muscles. Possible reflex adaptations related to high stretch loads in jumping and rapid reciprocal movements have also been revealed. Other studies, including those that demonstrate the "cross-training" effect and specificity of training, provide further evidence of neural adaptation. The possible mechanisms of neural adaptation are discussed in relation to motor unit recruitment and firing patterns. The relative roles of neural and muscular adaptation in short- and long-term strength training are evaluated.
.HÄKKUKINEN, K., KOMI, P.V. & ALÉN, M. 1985. Effect of explosive type strength training on isometric force‐ and relaxation‐time, electromyographic and muscle fibre characteristics of leg extensor muscles. Acta Physiol Scand 125, 587–600. Received 26 January 1985, accepted 9 May 1985. ISSN 0001–6772. Department of Biology of Physical Activity and Department of Health Sciences, University of Jyväskylä, Finland.
To investigate the influence of explosive type strength training on isometric force‐ and relaxation‐time and on electromyographic and muscle fibre characteristics of human skeletal muscle, 10 male subjects went through progressive training which included primarily jumping exercises without extra load and with light extra weights three times a week for 24 weeks. Specific training‐induced changes in force‐time curve were observed and demonstrated by great ( P < 0.05–0.001) improvements in parameters of fast force production and by a minor ( P< 0.05) increase in maximal force. The continuous increases in fast force production during the entire training were accompanied by and correlated with the increases ( P < 0.05) in average IEMG‐time curve and with the increase (P < 0.05) in the FT:ST muscle fibre area ratio. The percentage of FT fibres of the muscle correlated ( P < 0.05) with the improvement of average force‐time curve during the training. The increase in maximal force was accompanied by significant ( P < 0.05) increases in maximum IEMGs of the trained muscles. However, the hypertrophic changes, as judged from the anthropometric and muscle fibre area data, were only slight during the training. It can be concluded that in training for fast force production considerable neural and selective muscular adaptations may occur to explain the improvement in performance, but that genetic factors may determine the ultimate potential of the trainability of this aspect of the neuromuscular performance.
1. Skinfold thickness and body density were measured on 105 young adult men and women and 86 adolescent boys and girls.
2. The correlation coefficients between the skinfold thicknesses, either single or multiple, and density were in the region of −0.80.
3. Regression equations were calculated to predict body fat from skinfolds with an error of about ±3.5%.
4. A table gives the percentage of the body-weight as fat from the measurement of skin-fold thickness.
Volleyball players, middle distance runners and non-athletes (n = 10/group) were tested to determine whether neuromuscular differences existed between groups and to clarify the roles of factors involved in maximal power production. The runners were leaner than controls, while the volleyball players were taller, heavier and had larger thigh volumes than the other groups. The volleyball players had higher absolute cycle ergometer power than both middle distance (26%) and control (15%) groups, but differences disappeared when expressed relative to body mass or thigh volume. Volleyball athletes were also stronger than both middle distance (51, 52%) and control subjects (33, 35%) for isokinetic leg extension and plantar flexion respectively (0-4.19 rad.s-1). In leg press they were stronger than middle distance (32%) and control subjects (36%) for only the isometric and 1.05 rad.s-1 contraction. The volleyball players also had higher rates of isometric torque development than the other groups, however nerve conduction velocity did not vary. Vastus lateralis biopsy samples revealed no differences in percent Type II muscle fibers, or fiber cross-sectional area between groups, yet volleyball athletes had larger Type II/I fiber area ratio than controls (15%). Both strength, rate of torque development and power were related to muscle and muscle fiber size variables, but not fiber distribution or nerve conduction velocity. The size of type II muscle fibers seemed to be especially important since this was the only variable related to power when adjusted for body size.
We investigated the reproducibility of measurements of maximal voluntary torque and maximal voluntary activation using twitch interpolation. On 5 days, each of 5 subjects performed 10 maximal voluntary isometric contractions of their elbow flexors. Single supramaximal stimuli were delivered over biceps brachii at the measured peak torque during each effort, and in the relaxed muscle 5 s later. A voluntary activation score was calculated from the size of twitches evoked by the stimuli (resolution < 0.15 Nm). Although all subjects were able to drive the stimulated elbow flexor muscles maximally in some trials, they did not do so in 75% of all contractions. Maximal voluntary torques did not vary significantly within a subject between sessions. There were consistent differences in the level of maximal voluntary activation between subjects (P < 0.01), but no differences in voluntary activation within an individual across days in 4 of 5 subjects. Failure to drive the stimulated elbow flexor muscles maximally was not associated with inadvertent co-contraction of the antagonist muscles.
The relationships between absolute peak muscle power (W
peak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5′-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20–35 years; B, 9 S aged 35–50 years; C, 9 S aged more than 50 years; D, 13 children aged 8–13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The W
peak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The W
peak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in W
peak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of W
peak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.
The aim of the study was to examine if the twitch interpolation technique could be used to objectively measure fatigue in the quadriceps muscle in subjects performing submaximally. The 'true' maximum isometric quadriceps torque was determined in 21 healthy subject using the twitch interpolation technique. Then an endurance test was performed in which the subjects made repeated isometric contractions at 50% of the 'true' maximum torque for 4 s, separated by 6 s rest periods. During the test, the force response to single electrical stimulation (twitch amplitude) was measured at 50% and 25% of the estimated maximum torque. In 10 subjects, the test was repeated 2-4 weeks later. Twitch amplitudes at 50% of maximum torque declined exponentially with time in 20 of 21 subjects. The distribution of the exponential rate constant was skewed with a mean of 4.6 h-1 and range of 0.3-21.5 h-1. After logarithmical transformation, the distribution of the exponential rate constant fitted closely to a normal distribution, and the inter-individual variation was SD = 1.15 compared to an intra-individual variation of 0.29. The coefficient of correlation for repeated determination was 0.91 (P < 0.001, n = 10). In conclusion, the twitch technique can be used for objectively measuring fatigue of the quadriceps muscle.
Quadriceps muscle and fibre cross-sectional areas (CSA), torque and neural activation were studied in seven healthy males during 6 months of weight training on alternate days with six series of eight unilateral leg extensions at 80% of one repetition maximum. After training, the quadriceps cross-sectional area increased by 18.8 +/- 7.2% (P < 0.001) and 19.3 +/- 6.7% (P < 0.001) in the distal and proximal regions respectively, and by 13.0 +/- 7.2% (P < 0.001) in the central region of the muscle. Hypertrophy was significantly different between and within the four constituents of the quadriceps. Biopsies of the vastus lateralis at mid-thigh did not show any increase in mean fibre cross-sectional area. Maximum isometric voluntary torque increased by 29.6 +/- 7.9%-21.1 +/- 8.6% (P < 0.01-0.05) between 100 degrees and 160 degrees of knee extension, but no change in the optimum angle (110 degrees-120 degrees) for torque generation was found. A 12.0 +/- 10.8% (P < 0.02) increase in torque per unit area together with a right shift in the IEMG-torque relation and no change in maximum IEMG were observed. Time to peak isometric torque decreased by 45.8% (P < 0.03) but no change in time to maximum IEMG was observed. In conclusion, strength training of the quadriceps results in a variable hypertrophy of its components without affecting its angle-torque relation. The increase in torque per unit area, in the absence of changes in IEMG, may indicate changes in muscle architecture. An increase in muscle-tendon stiffness may account for the decrease in time to peak torque.
In this study we directly tested the hypothesis that isometric strength training increases voluntary drive to muscles. In addition, it was attempted to replicate the findings of an earlier study that showed imagined training increases voluntary strength as much as actual training, as this finding provides key support for the hypothesis that training increases voluntary drive (Yue & Cole 1992). Fifty-four subjects were randomly allocated to groups that performed 8 weeks of isometric training of the elbow flexor muscles, imagined isometric training, or a control task involving the lower limbs. Voluntary isometric strength and activation of the elbow flexor muscles were measured before and after training. Voluntary activation was measured with a sensitive form of twitch interpolation. Training, imagined training and control groups increased voluntary isometric elbow flexor strength by means of 17.8% (+/- 3.1 SEM), 6.8% (+/- 2.6) and 6.5% (+/- 3.0), respectively. The training group increased in strength significantly more than imagined training and control groups (P = 0.01 for both comparisons), but the small difference between imagined training and control groups was not significant (P = 0.31). Prior to training, voluntary activation of all subjects was high (96.2 +/- 0.5%). This did not change significantly with training and there were no significant differences between groups. These data challenge the hypothesis that training of the elbow flexor muscles increases isometric strength by inducing adaptations of the central nervous system, because they show that training does not increase voluntary activation and imagined training does not increase strength.
A group of 32 healthy men (M) divided into three different age groups, i.e. M20 years [mean 21 (SD 1); n = 12], M40 [mean 40 (SD 2); n = 10] and M70 [mean 71 (SD 5); n = 10] volunteered as subjects for examination of maximal and explosive force production of leg extensor muscles in both isometric and dynamic actions (squat jump, SJ and counter movement jump, CMJ, and standing long-jump, SLJ). The balance test was performed on a force platform in both isometric and dynamic actions. Maximal bilateral isometric force value in M70 was lower (P < 0.001) than in M40 and as much as 46% lower (P < 0.001) than that recorded in M20 (P < 0.001). The maximal rate of force development (RFD) on the force-time curve was in M70 lower (P < 0.001) than in M40 and as much as 64% lower than in M20. The heights in SJ and CMJ and the distance in SLJ in M70 were lower (P < 0.001) than in M40 and M20 (P < 0.001). In response to modifications of the visual surroundings the older subjects were 24%-47% (P < 0.05 and P < 0.001) slower in their response time in reaching the lit centre (TT) and remained 20%-34% (P < 0.001) less time inside the centre (TC) from the overall time of lighting than M40 and M20, respectively. In both older groups the individual values of isometric RFD correlated significantly (P < 0.05) with the individual balance values of TT and TC. The present results would suggest that the capacity for explosive force production declines drastically with increasing age, even more than maximal muscle strength. Aging may also lead to impaired balance with a decrease in event detection and speed of postural adjustments. The decreased ability to develop force rapidly in older people seems to be associated with a lower capacity for neuromuscular response in controlling postural sway.