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Regional Surface Electromyography of the Vastus Lateralis During Strength and Power Exercises
Abstract
Neuromuscular activation during and chronic adaptation from exercise are innately linked and both can vary along a muscle's length. During high-force and high-speed exercise intramuscular hypertrophy follows set patterns that provide the greatest biomechanical advantages. However it's unknown if muscle activity as recorded by surface electromyography (sEMG) will follow these patterns. The purpose of the present study was to compare vastus lateralis intramuscular sEMG during the heavy squat (HS) and unloaded jump squat (JS) exercises. Ten subjects performed HS with 80% of maximum load and unloaded JS to parallel-depth, while intramuscular peak- and mean-sEMG were measured at 33% (Proximal), 50% (Middle), and 67% (Distal) thigh length. Muscle activity was compared between regions and exercises using a 3x2 repeated measures ANOVA with Bonferoni post-hoc corrections. Peak-sEMG was greater proximally in JS than HS (p=0.033), but similar in the middle and distal-regions (p=0.521, 0.594 respectively) while mean-sEMG was similar between all regions (p=0.150-0.979). In addition, a main effect was found in which peak and mean-sEMG were greater proximally than the middle and distal-regions (p=0.001, 0.006). Muscle activity measured using sEMG displayed dissimilar patterns to previously observed regional hypertrophy. Specifically, while previous research found greater proximal hypertrophy in JS than HS, in the present study peak-sEMG was greater in HS than JS. Furthermore, distally where HS elicited greater hypertrophy than JS no differences in sEMG were present. Thus, regional-sEMG appears not to be a viable tool for predicting differences in regional-hypertrophy, most likely due to technological constraints and intramuscular differences in muscle structure.
... Given the previously observed changes regional hypertrophy in response to different training conditions and their potential impact these changes on running performance, there is a clear benefit to developing methods to predict hypertrophy patterns in response to different training stresses. Along these lines, previous studies have found that patterns of hypertrophy can be predicted from regionspecific, post-exercise changes in intramuscular fluid accumulation measured using T 2 -weighted MRI (Wakahara et al., 2012;Wakahara et al., 2013;Wakahara et al., 2017), while regional muscle activity during exercise measured by electromyography (EMG) are unrelated to patterns of hypertrophy (Miyamoto et al., 2013;Earp et al., 2016). Presently, no studies have determined if patterns of hypertrophy can be predicted by near infrared spectroscopy (NIRS), which provides information about changes in localized muscle oxygenation and is more fundamentally similar to T 2 -weighted MRI than EMG while having a lower research cost compared to T 2 -weighted MRI. ...
... While the mechanisms driving region-specific hypertrophy are yet to be explicitly determined, several potential factors have been identified, including proximo-distal variation in muscle architecture (fascicle angle, fascicle length and cross-sectional area), fiber type distribution, and selective muscle/regional activation (Wakahara et al., 2012;Wakahara et al., 2013;Franchi et al., 2014;Earp et al., 2016;Wakahara et al., 2017). The variations in all of these components have been previously hypothesized to allow for specific portions of a muscle to specialize in specific exercise conditions (Wakahara et al., 2017). ...
... In contrast, selective activation of specific regions of a muscle cannot be discounted. While previous studies have found that muscle activity measured using EMG was unrelated to patterns of hypertrophy (Miyamoto et al., 2013;Earp et al., 2016), others have found that patterns of hypertrophy can be predicted using T 2 -weighted MRI (Wakahara et al., 2012;Wakahara et al., 2013;Wakahara et al., 2017). Unlike EMG, which measures the propagation of electrical signals throughout the muscle during exercise, T 2 -weighted MRI measures changes in intramuscular fluid accumulation after exercise. ...
Purpose: To determine whether kinetic chain pattern during knee extensor strength training influences quadriceps femoris center of mass and moment of inertia about the hip in a predictable manner as such changes can affect running economy. Methods: Twelve participants completed 8 weeks of both unilateral open (OKC) and closed (CKC) kinetic chain resistance training on opposing legs. Changes in quadriceps femoris muscle volume (VOLQF), center of mass location (CoMQF), and moment of inertia (I QF) about the hip were determined from magnetic resonance images scans. Regional hemodynamics of the vastus lateralis taken at 30% and 70% of muscle length during OKC and CKC bouts early in the training program were measured using near-infrared spectroscopy (NIRS) and used post hoc to predict changes in CoMQF. Results: While increases in VOLQF were similar between OKC (Δ79.5 ± 87.9 cm3) and CKC (Δ60.2 ± 110.5 cm3, p = 0.29), the patterns of hypertrophy differed; a distal shift in CoMQF (Δ2.4 ± 0.4 cm, p < 0.001) and increase in I QF (Δ0.017 ± 0.014 kg m2, p < 0.001) occurred in OKC but not in CKC (CoMQF: Δ-2.2 ± 2.0 cm, I QF: Δ-0.022 ± 0.020 kg m2, p > 0.05). Regional hemodynamics assessed by NIRS during a single training session displayed similar exercise and regional differences and predicted 39.6% of observed changes in CoMQF. Conclusions: Exercise selection influences muscle shape sufficiently to affect CoMQF and I QF, and these changes may be predicted in part from NIRS measurements during a single workout. Given I QF is inversely related to running economy and since CKC exercise provides a more proximal pattern of hypertrophy than OKC, it may be more preferential for running. The results from the present study also highlight the potential of NIRS as a tool for predicting patterns of hypertrophy between different exercises and exercise conditions.
... These mean values were normalized to the MVIC data. A 500-millisecond window length was used for RMS calculations (Earp et al., 2016;Evans et al., 2019). All EMG data analyses were performed with Delsys EMGworks Analysis software (Delsys, Boston, MA, USA). ...
In this study, it was aimed to compare the vastus medialis and vastus lateralis muscle activations during squat exercises performed on different surfaces. 14 males took part in this study. A ground surface is used as a stable surface, a gymnastics mat and a Bosu ball are used as an unstable surface. Participants performed 2 sets of squats on 3 surfaces and 10 repetitions of each set. Participants performed squat exercises with their own body weight. Muscle activation measurements were made from the vastus medialis and vastus lateralis muscles during the squat movement on each surface. A one-way repeated-measures analysis of variances was used for the statistical comparison of muscle activations between surfaces. As a result of statistical analysis, no significant differences were found in the vastus medialis and vastus lateralis muscle activations between surfaces (p>0.05). In conclusion, it was determined that the vastus medialis and vastus lateralis muscle activation in the squat movement was not affected by the stability of the surfaces.
... The muscular tension evoked during contraction has been proposed to be a primary mechanism to trigger skeletal muscle hypertrophy [24]. Similar to the proposed association between regional hypertrophy and localized activity [25,26], we speculate that the magnitude of regional muscle size may relate to the stiffness during contraction. This topic is worthy of future investigation. ...
This study sought to investigate whether the stiffness of the biceps femoris long head differs between proximal and distal regions during isometric knee flexion at different contraction intensities and muscle lengths. Twelve healthy individuals performed knee flexion isometric contractions at 20% and 60% of maximum voluntary isometric contraction, with the knee flexed at 15 and 45 degrees. Muscle stiffness assessment was performed using ultrasound-based shear wave elastography. Proximal and distal regions of the biceps femoris long head were assessed. Biceps femoris long head muscle showed a greater stiffness (i) in the distal region, (ii) at higher contraction intensity, and (iii) at longer muscle length. The proximal-to-distal stiffness ratio was significantly lower than 1 (i.e., heterogenous) at lower contraction intensity regardless of the muscle length. However, this was not observed at higher contraction intensity. This study is the first to show heterogeneity in the active stiffness of the biceps femoris long head. Given the greater incidence of injury at the proximal region of biceps femoris long head, this study opens new directions for future research. Additionally, the present study results indicate that studies assessing muscle stiffness at one single muscle region should be interpreted with caution.
... CSA, cross-sectional area. associations between regional electromyographic activity and regional muscle hypertrophy (12,30). Thus, to better understand the mechanisms that underline regional hypertrophy, future studies could measure muscle activation (T2 and EMG) and muscle tissue oxygen desaturation responses in different QF muscles lengths during dynamic RT protocols with different torque-angle relationships. ...
The manipulation of the muscle action duration (MAD) can influence the instantaneous torque along the range of motion, which can lead to adaptations of regional muscle hypertrophy. The aim of this study was to compare the effects of matched resistance training (RT) on the knee extension machine with different MAD in the cross-sectional area (CSA) responses within the quadriceps femoris (QF) and its muscles. Forty-four subjects were allocated into a control and 3 experimental groups. For a period of 10 weeks, subjects in the experimental groups performed the training protocols that were different only by the MAD: group 5c1e (5s concentric action [CON] and 1s eccentric action [ECC]; group 3c3e (3s CON and 3s ECC) and group 1c5e (1s CON and 5s ECC). Magnetic resonance imaging was performed (before and after the intervention) to determine the relative change (%) in CSA of the QF muscles along proximal (30%), middle (50%), and distal regions (70% distal of the femur). The change in CSA of the rectus femoris at the middle region are greater in 5c1e (6.8 ± 6.5%) and 1c5e (7.4 ± 6.0%) groups than 3c3e (3.4 ± 6.6%) and control groups (0.2 ± 1.8%). In addition, vastus lateralis at the distal region (5c1e = 15.9 ± 11.8%; 1c5e = 14.4 ± 10.0%) presenting greater increases in change of CSA than the others vastus only 5c1e (vastus lateralis [VI] = 5.0 ± 4.7%; vastus medialis [VM] = 4.2 ± 3.2%) and 1c5e groups (VI = 4.7 ± 3.6%; VM = 3.4 ± 3.1%). In conclusion, this study showed that matched RT protocols with different MAD resulted in different region-specific muscle hypertrophic across the individual muscles of QF.
... All participants performed two exercise sessions that were 48 h apart, thus avoiding the effects of muscle fatigue [27]. The first session was focused on familiarization with the exercises and the determination of 5 repetitions maximum (5 RM). ...
The Monopodal Squat, Forward Lunge and Lateral Step-Up exercises are commonly performed with one's own body weight for rehabilitation purposes. However, muscle activity evaluated using surface electromyography has never been analyzed among these three exercises. Therefore, the objectives of the present study were to evaluate the amplitude of the EMG activity of the gluteus medius, gluteus maximus, biceps femoris, vastus lateralis, vastus medialis and rectus femoris muscles in participants performing the Lateral Step-Up, Forward Lunge and Monopodal Squat exercises. A total of 20 physically active participants (10 men and 10 women) performed 5 repetitions at 60% (5 repetition maximum) in each of the evaluated exercises. The EMG amplitude was calculated in percentage of the maximum voluntary contraction. The Monopodal Squat exercise showed a higher EMG activity (p ≤ 0.001) in relation to the Lateral Step-Up and Forward Lunge exercises in all of the evaluated muscles (d > 0.6) except for the rectus femoris. The three exercises showed significantly higher EMG activity in all of the muscles that were evaluated in the concentric phase in relation to the eccentric one. In the three evaluated exercises, vastus lateralis and vastus medialis showed the highest EMG activity, followed by gluteus medius and gluteus maximus. The Monopodal Squat, Forward Lunge and Lateral Step-Up exercises not only are recommended for their rehabilitation purposes but also should be recommended for performance objectives and strength improvement in the lower limbs.
... This is going to be governed by the mechanics of each muscle in relation to the exercise. Practically this means that hyper trophy may not occur at a uniform rate throughout a muscle as a result of exercise (Earp et al., 2016;Folland and William 2007;Schoenfeld et al. 2015). ...
... The relative alignment and movement of muscle fibres, location of the innervation zone, and cross-talk between muscles is known to influence EMG signal intensity and quality (Basmajian and DeLuca, 1985;Beck et al., 2010;Farina et al., 2002;Rainoldi et al., 2000;Rainoldi et al., 2004). Varying the position of the electrodes can change the recorded Vastus Lateralis muscle activity by 28-44% during weighted squats and jumping (Earp et al., 2016). Normalisation of muscle activity values, as performed in this study, attenuates issues with the positioning of electrodes and location of the innervation zone in EMG recording of Vastus Lateralis activity (Beck et al., 2008). ...
Widespread use of electromyography (EMG) as an assessment and biofeedback method may be limited by costly commercial systems. Low-cost devices are available; however their validity is unknown. This study determined the concurrent validity of a low-cost EMG on a microchip compared with a commercially available system during isometric and dynamic muscle contractions. Inter-tester, intra-session reliability of manual data extraction during data processing compared to a simple, automatic thresholding method using the Teager-Kaiser energy operator (TKEO) was also evaluated. 10 healthy women (age 28.1 ± 6.8 yrs, height 162.1 ± 6.8 cm, mass 60.3 ± 10.2 kg) were assessed simultaneously with a commercially available EMG system (Telemyo DTS) and a custom low-cost EMG system (Myoware Muscle Sensor) during voluntary isometric contractions, knee extension, squatting, stepping and jumping. Two surface electrode sets (connected to the low-cost and the commercial system) were placed end to end along the same Vastus Lateralis muscle fibre line. Peak and mean contraction intensity, and contraction duration were analysed. Overall the relative agreement between systems was excellent for peak muscle activation (ICC 0.77-0.96) and modest to excellent for mean muscle activation (ICC 0.68-0.95) and contraction duration (ICC 0.65-0.99). Inter-tester, intra-session reliability was excellent for peak contraction intensity (ICC > 0.99) and modest to excellent for mean contraction intensity, with the TKEO method primarily recording stronger agreement than the manual method. Poor to excellent inter-tester reliability occurred for contraction duration. Our findings indicate that a low-cost EMG system is comparable to a commercial system for assessing muscle activation, and that using the TKEO improved the reliability of timing related variables.
... 4,62,63 Other studies confirm the greater muscle activation during FW resistance training 29,36,64 while others do not. 35 Although muscle activity will not explain muscle hypertrophy 65,66 it will explain the intensity of a muscle's contraction. Hence, a combination of muscle activity and muscle hypertrophy outcomes will be needed to monitor both training adaptations. ...
Objective:
The primary aim of this systematic review was to determine if inertial flywheel resistance training is superior to gravity-dependent resistance training in improving muscle strength. The secondary aim was to determine whether inertial flywheel resistance training is superior to gravity-dependent resistance training in improving other muscular adaptations.
Design:
A systematic review with meta-analyses of randomised and non-randomised controlled trials.
Methods:
We searched MEDLINE, Scopus, SPORTDiscus, Web of Science and Cochrane Central Register of Controlled Trials with no publication date restrictions until November 2016. We performed meta-analyses on randomised and non-randomised controlled trials to determine the standardized mean difference between the effects of inertial flywheel and gravity-dependent resistance training on muscle strength. A total of 76 and 71 participants were included in the primary and secondary analyses, respectively.
Results:
After systematic review, we included three randomised and four non-randomised controlled trials. In the primary analysis for the primary outcome muscle strength, the pooled results from randomised controlled trials showed no difference (SMD=-0.05; 95%CI -0.51 to 0.40; p=0.82; I(2)=0%). In the secondary analyses of the primary outcome, the pooled results from non-randomised controlled trials showed no difference (SMD=0.02; 95%CI -0.45 to 0.49; p=0.93; I(2)=0%; and SMD=0.03; 95%CI -0.43 to 0.50; p=0.88; I(2)=0%). Meta-analysis on secondary outcomes could not be performed.
Conclusion:
Based on the available data, inertial flywheel resistance training was not superior to gravity-dependent resistance training in enhancing muscle strength. Data for other strength variables and other muscular adaptations was insufficient to draw firm conclusions from.
... Our results show that: (i) variations in EMG amplitude during squat may be not of neural origin (cf. Figs. 2 and 3), which possibly explain the inconsistencies recently observed in EMG and architectural, RF responses to squat exercises (Earp et al., 2016); (ii) when controlled for anatomical factors, EMGs detected proximally from RF are significantly greater than those collected distally from the muscle. The possibility of predicting muscle adaptation following squat exercises from surface EMGs is a relevant, open issue. ...
Recent evidence suggests different regions of the rectus femoris (RF) muscle respond differently to squat exercises. Such differential adaptation may result from neural inputs distributed locally within RF, as previously reported for iso- metric contractions, walking and in response to fatigue. Here we therefore investigate whether myoelectric activity dis- tributes evenly within RF during squat. Surface electromyograms (EMGs) were sampled proximally and distally from RF with arrays of electrodes, while thirteen healthy volunteers performed 10 consecutive squats with 20% and 40% of their body weight. The root mean square (RMS) value, computed separately for thirds of the concentric and eccentric phases, was considered to assess the proximo-distal changes in EMG amplitude during squat. The channels with varia- tions in EMG amplitude during squat associated with shifts in the muscle innervation zone were excluded from analysis. No significant differences were observed between RF regions when considering squat phases and knee joint angles indi- vidually (P > 0.16) while a significant interaction between phase and knee joint angle with detection site was observed (P < 0.005). For the two loads considered, proximal RMS values were greater during the eccentric phase and for the more flexed knee joint position (P < 0.001). Our results suggest inferences on the degree of RF activation during squat must be made cautiously from surface EMGs. Of more practical relevance, there may be a potential for the differential adaption of RF proximal and distal regions to squat exercises.
BACKGROUND: In the last decades, emerging evidence has shown that muscle growth is not homogeneous along a muscle head. This phenomenon is known as regional muscle hypertrophy and has led to several questions regarding the implications it may have for health and sports performance. OBJECTIVE: The aim of this study was to determine whether regional hypertrophy can be predicted by surface electromyography (sEMG). METHODS: 36 participants performed two arm exercises (preacher curls and inclined curls) in a random order to muscle failure at 70% of the 1 RM of the bicep curl exercise. As every participant performed a different number of repetitions, Peak sEMG and the integral of the sEMG of the last 3 repetitions was analyzed an compared to previously performed maximal voluntary isometric contractions (MVIC). RESULTS: The independent sample t-tests showed no significant differences neither in the peak nor in the integral of the sEMG between exercises for any given region. CONCLUSIONS: sEMG cannot be used to predict regional hypertrophy.
Acute changes in muscle architecture influenced by muscle swelling might be associated with chronic adaptations to resistance exercise, including skeletal muscle growth. Concentric (CON) and eccentric (ECC) muscle actions both play a role in hypertrophic processes, but the influence of each on acute indices of muscle swelling [i.e. muscle thickness (MT) and pennation angle PA)] remain relatively unknown. Therefore, this study compared the acute changes in MT and PA in response to work-matched CON versus ECC isokinetic exercise. Twelve university-aged students performed two bouts of maximal isokinetic knee extensions at 120 deg·s-1 on the same day: 50 CON followed by a work-matched ECC bout (~5000 J; 28±5 reps) with the contralateral limb. Ultrasound images were captured from the middle and distal sites of the vastus lateralis before and immediately after each exercise bout. From these images, MT and PA were measured. Middle and distal MT (11-14%, respectively, p<0.001) and middle PA (39%, p<0.001) increased only after CON. Additionally, changes in MT were strongly related to the amount of total work performed (r=0.76) during CON. Our results suggest that when the workload is matched between CON and ECC muscle actions performed at a moderate velocity, CON actions seem to be a more potent stimulus for inducing acute changes in muscle thickness and pennation angle.
The State of the Art on Sensors and Sensor Placement Procedures for Surface ElectroMyoGraphy: A proposal for sensor placement procedures, Deliverable of the SENIAM project, is a publication of the SENIAM project, published by Roessingh Research and Development b.v. ISBN 90-75452-09-8. PREFACE SENIAM, Surface EMG for the Non-Invasive Assessment of Muscles, is a concerted action, funded by the European Commission as part of the Biomed 2 Research Program. The aim of concerted actions is to facilitate and enhance international co-operation in promising fields of specific interest. The SENIAM project has two objectives: In the first place SENIAM will enable scientists and clinicians working with Surface EMG (SEMG) to exchange knowledge and experience on both basic and applied aspects of SEMG. With respect to this, it is important to notice that the 16 partners originate from many different disciplines, like rehabilitation, orthopaedics, neurology, ergonomy, sports, psychology, all with largely different specific knowledge and experience on SEMG. SENIAM brings together for the first time this variety of knowledge and experience, enabling exchange and discussion and the creation of a European common body of knowledge on SEMG. The second objective of SENIAM is to develop recommendations for key items in the use of SEMG that presently prevent a useful exchange of data and knowledge and a further maturation of the field. The key items concern: sensors, sensor placement, signal processing and modelling. The development of recommendations is essential to bring SEMG a major step forward as a general tool to be used in many applications focused on the assessment of the functioning and status of the neuromuscular system. The creation of consensus on the key items will enable exchange of information and experience and as such a rapid increase of the common body of knowledge. The present report is a major achievement in the SENIAM project. It comprises the state of the art on sensors and sensor placement, the obtained consensus about recommendations in order to optimise the sensor configuration as well as a first proposal for the standardisation of the electrode placement on more then 20 muscles. As it is well known, the choice of the sensor configuration as well as the placement on the muscle has a major effect on the SEMG characteristics, so it is felt extremely important that consensus on these items has been obtained. Nevertheless one has to realise that such recommendations will never be finished. The scientific and clinical progress being made in this field will cause that these recommendations have to be updated from time to time. The present results provide a firm basis to start from and in that sense it is something a lot of application focused EMG-users have been waiting for a long time. Finally I would like to express my sincere thanks to all the experts in the field that have contributed to this report. In addition to this, I would like to thank especially Bart Freriks, Cathy Disselhorst-Klug and Roberto Merletti, who have made a major contribution especially with respect to the inventory on the actual use of the sensors and the guidelines for reporting as well as Bart Freriks for his assistance in compiling all the knowledge into this report.
Tendon stiffness increases as the magnitude and rate of loading increases, according to its viscoelastic properties. Thus, under some loading conditions tendons should become exceptionally stiff and act almost as rigid force transducers. Nonetheless, observations of tendon behavior during multi-joint sprinting and jumping tasks have shown that tendon strain increases whilst muscle strain decreases as the loading intensity increases. The purpose of the current study was to examine the influence of external loading intensity on muscle–tendon unit (MTU) behavior during a high-speed single-joint, stretch-shortening cycle (SSC) knee extension task. Eighteen men (n = 9) and women (n = 9) performed single-leg, maximum intensity SSC knee extensions at loads of 20, 60 and 90 % of their one repetition maximum. Vastus lateralis fascicle length (L
f) and velocity (v
f) as well as MTU (L
MTU) and tendinous tissue (L
t) length were measured using high-speed ultrasonography (96 Hz). Patellar tendon force (F
t) and rate of force development (RFDt) were estimated using inverse dynamics. Results showed that as loading intensity increased, concentric joint velocity and shortening v
f decreased whilst F
t and RFDt increased, but no significant differences were observed in eccentric joint velocity or peak L
MTU or L
f. In addition, the tendon lengthened significantly less at the end of the eccentric phase at heavier loads. This is the first observation that tendon strain decreases significantly during a SSC movement as loading intensity increases in vivo, resulting in a shift in the tendon acting as a power amplifier at light loads to a more rigid force transducer at heavy loads.
The purpose of this study was to investigate whether changes in angular velocity would alter vastus lateralis (VL) and rectus femoris (RF) oxygenation status during maximal isokinetic knee extension exercises. Eleven recreationally active male participants randomly performed ten maximal knee extensions at 30, 60, 120 and 240° s(-1). Tissue oxygenation index (TOI) and total haemoglobin concentration ([tHb]) were acquired from the VL and RF muscles by means of near-infrared spectroscopy (NIRS). Breath-by-breath pulmonary oxygen consumption (VO(2p)) was recorded throughout the tests. Peak torque and VO(2p) significantly decreased as a function of velocity (P<0·05). Interestingly, RF and VL TOI significantly increased as a function of velocity (P<0·05), whereas [tHb] significantly decreased as a function of velocity (P<0·05). A greater number of muscle fibre recruited at slow velocity, where the torque and VO(2p) were the highest, might explain the lower VL and RF TOI observed herein. Furthermore, the increase in local blood flow (suggested by [tHb] changes) during isokinetic knee extension exercises performed at slow angular velocity might have been induced by a higher intramuscular pressure during the contraction phases as well as a greater microcirculatory vasodilatation during relaxation phases. Implementing slow-velocity isokinetic exercises in rehabilitation or other training programmes could delay the short-term anoxia generated by such exercises and result in muscle metabolism enhancement.
In order to determine the total number of fibres and the extent to which the relative occurrence of different fibre types varies within m. vastus lateralis, 15 micrometers thick cross-sections of whole muscles were prepared. The total number of type 1 and type 2 fibres was determined in every 48th square millimetre of the section, and the results thus obtained were analysed using a computer program allowing an assessment of bivariate data in the form of contour plots. The total number of fibres varied both in proximal to distal direction in the same muscle and between individuals. No obvious correlation existed between the mean fibre area and the muscle cross-sectional area. The proportion of type 1 fibres in the whole muscle varied between individuals (from 44% to 57%) with a mean value for all five of 52%. The distribution of different fibre types varied within the muscle, mainly as a function of depth, with a predominance to type 2 fibres at the surface and type 1 fibres in deeper regions of the muscle. Thus, the fibre type distribution in m. vastus lateralis is not random. This must be taken into consideration when data on fibre type composition are compared with functional variables.
The purpose of this study was to compare architectural characteristics of leg muscles of sprinters and distance runners.
Skeletal muscle architectural characteristics were studied in 23 elite male 100-m sprinters (SPR, 10.0-10.9 s for 100 m), 24 elite male distance runners (DR, 13.5-14.5 min for 5000 m), and 24 untrained male controls. Fascicle pennation angle and isolated muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured in vivo by ultrasound, and fascicle length was estimated.
Standing height and upper and lower limb lengths were similar among the groups. Body weight was significantly greater in SPR than in either DR or controls, which were similar. Muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles was significantly greater in SPR than in either DR or controls, which were similar. In all muscles, pennation angle was similar between SPR and controls, but less than DR. Fascicle length of the vastus lateralis muscle (absolute and relative to limb length) was greatest in SPR and least in DR with control values being between the athlete groups. Fascicle length of the gastrocnemius medialis muscle (absolute and relative to limb length) was greater in SPR than in either DR or controls, which were similar. Fascicle length of the gastrocnemius lateralis muscle (absolute and relative to limb length) was significantly greater in SPR than DR. Absolute fascicle length in gastrocnemius lateralis muscle was similar between DR and controls; however, relative to limb length DR was significantly less.
Greater fascicle length and lesser pennation angle observed in leg muscles of SPR, compared with DR, would appear to favor shortening velocity as required for greater running speed.
Previous studies have reported inhomogeneous changes in quadriceps femoris (QF) cross-sectional area (CSA) in response to strength training. It is assumed that these differential changes in muscle shape influence the muscle's functional capacity during high-force and high-power movements. The purpose of the current study was to compare inter- and intra-muscular QF adaptations to high-load strength training and fast-speed power training.
36 non-strength-trained men were randomly assigned to 4 groups and completed 8 weeks of parallel-depth heavy squat-lift training (HS-P), parallel-depth jump squat training (JS-P), volitional-depth jump squat training (JS-V) or no training (C). QF, vastus lateralis (VL), intermedius (VI), medialis (VM) and rectus femoris (RF) CSA were measured in distal-, mid- and proximal-thigh regions using extended field-of-view ultrasonography and compared using a 3×2 mixed-model MANOVA with Bonferroni post-hoc tests (p<0.05).
HS-P and JS-P elicited similar changes in mid-CSAQF as well as summed-CSA of the QF, VL, VI and VM. CSAVL and CSAVI increased in both HS-P and JS-P at mid-thigh, but only JS-P significantly increased CSA proximally and only HS-P distally. CSAVM increased in HS-P and JS-P distally, but only HS-P at mid-thigh. No hypertrophy was observed in RF at any location and no significant differences were observed between JS-P and JS-V. HS-P elicited greater proximal hypertrophy in each of the vasti muscles while only JS-P elicited distal VL and VI hypertrophy.
These observed inhomogeneous changes in CSA may alter the thigh's moment of inertia and moment arms of muscle 'compartments', and the influence of elastic component force transmission on the muscular force expression. Such selective hypertrophy is speculated to be biomechanically beneficial to high-force or high-power movements used in training.
Previous studies have reported for the vastus lateralis (VL) that the extent of muscle hypertrophy in response to resistance training is greater in the distal than in the middle region, despite uniform muscle fibre composition within VL along its length. In the present study, to investigate mechanism(s) for such non-uniform muscle hypertrophy, we simultaneously measured neuromuscular activity and muscle oxygenation state at the middle and distal regions of VL during fatiguing heavy resistance exercise. Twelve males performed unilateral knee extension exercise which consisted of 4 sets of 8 repetitions at intensity of 80% of the individual one repetition maximum. During the resistance exercise, neuromuscular activities and muscle oxygenation status at the middle and distal regions (50% and 70% of the thigh length, respectively) of VL were measured by using electromyography and near-infrared spectroscopy, respectively. Neuromuscular activities were similar between the distal and middle regions of VL, whereas muscle tissue oxygenation saturation was significantly lower at the distal than at the middle region of VL. These results suggest a possibility that the regional difference in muscle oxygenation but not in neuromuscular activity during fatiguing heavy resistance exercise is responsible for the regional difference in hypertrophy within a muscle.
Purpose:
Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session.
Methods:
Twelve young men participated in a training intervention program for the elbow extensors with a multijoint resistance exercise for 12 wk (3 d · wk(-1)). Before and after the intervention, cross-sectional areas of the triceps brachii along its length were measured with magnetic resonance images. A series of transverse relaxation time (T2)-weighted magnetic resonance images was recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1 SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle and used as an index of muscle activation (percent activated area).
Results:
The percent activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in cross-sectional area induced by the training intervention was also significantly greater in the middle regions than the most proximal region.
Conclusion:
The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session.
The purpose of this study was to examine if the regional difference in muscle hypertrophy after chronic resistance training is associated with muscle activation after one session of resistance exercise. Twelve men performed one session of resistance exercise of elbow extensors. Before and immediately after the exercise, transverse relaxation time (T2)-weighted magnetic resonance (MR) images of upper arm were recorded to evaluate the muscle activation along its length. In the MR images, T2 for the pixels within the triceps brachii muscle was quantified. The number of pixels with T2 greater than the threshold (mean + 1SD of T2 before the exercise) was expressed as the ratio to the number of pixels occupied by the muscle (%activated area). Another 12 subjects completed 12 weeks of training intervention (3 days per week), which consisted of the same program variables as used in the experiment for the T2 measurement. The cross-sectional areas of the triceps brachii before and after the training intervention were measured from MR images of upper arm. The %activated area of the triceps brachii induced by one session of the exercise was found to be significantly lower in the distal region than the middle and proximal regions. Similarly, the relative increase in muscle cross-sectional area after the 12 weeks of training intervention was significantly less in the distal region than the middle and proximal regions. The results suggest that the regional difference in muscle hypertrophy after chronic resistance training is attributable to the regional difference in muscle activation during the exercise.
The purpose of this study was to compare the relationship between surface electromyography (EMG) and knee joint angle of the vastus intermedius muscle (VI) with the synergistic muscles in the quadriceps femoris (QF) muscle group. Fourteen healthy men performed maximal voluntary contractions during isometric knee extension at four knee joint angles from 90°, 115°, 140°, and 165° (180° being full extension). During the contractions, surface EMG was recorded at four muscle components of the QF muscle group: the VI, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles. The root mean square of the surface EMG at each knee joint angle was calculated and normalized by that at a knee joint angle of 90° for individual muscles. The normalized RMS of the VI muscle was significantly lower than those of the VL and RF muscles at the knee joint angles of 115° and 165° and those of the VL, VM, and RF muscles at the knee joint angle of 140° (P<0.05). The present results suggest that the neuromuscular activation of the VI muscle is regulated in a manner different from the alteration of the knee joint angle compared with other muscle components of the QF muscle group.
The purpose of this study was to evaluate whether and how isometric multijoint leg extension strength can be used to assess athletes' muscular capability within the scope of strength diagnosis. External reaction forces (Fext) and kinematics were measured (n = 18) during maximal isometric contractions in a seated leg press at 8 distinct joint angle configurations ranging from 30 to 100° knee flexion. In addition, muscle activation of rectus femoris, vastus medialis, biceps femoris c.l., gastrocnemius medialis, and tibialis anterior was obtained using surface electromyography (EMG). Joint torques for hip, knee, and ankle joints were computed by inverse dynamics. The results showed that unilateral Fext decreased significantly from 3,369 ± 575 N at 30° knee flexion to 1,015 ± 152 N at 100° knee flexion. Despite maximum voluntary effort, excitation of all muscles as measured by EMG root mean square changed with knee flexion angles. Moreover, correlations showed that above-average Fext at low knee flexion is not necessarily associated with above-average Fext at great knee flexion and vice versa. Similarly, it is not possible to deduce high joint torques from high Fext just as above-average joint torques in 1 joint do not signify above-average torques in another joint. From these findings, it is concluded that an evaluation of muscular capability by means of Fext as measured for multijoint leg extension is strongly limited. As practical recommendation, we suggest analyzing multijoint leg extension strength at 3 distinct knee flexion angles or at discipline-specific joint angles. In addition, a careful evaluation of muscular capacity based on measured Fext can be done for knee flexion angles ≥ 80°. For further and detailed analysis of single muscle groups, the use of inverse dynamic modeling is recommended.
The examination of moment and electromyographic (EMG) activity-angle curves of the agonists and antagonists is important for the determination of the mechanisms responsible for moment production during maximal activation of knee extensors and flexors. The purpose of this study was the examination of agonist and antagonistic activity of knee extensors and flexors at different knee joint angles during isokinetic exercise. Twelve females performed maximum isometric, eccentric and concentric isokinetic efforts of knee extensors and flexors on a Biodex dynamometer. The isokinetic tests were performed at angular velocities of 30, 60, 90, 120 and 150°/s. The EMG activity of vastus lateralis, rectus femoris, vastus medialis and hamstrings was also recorded. The knee extensor and flexor maximal activity was found at angles ranging from 50°to 70°and from 20°to 40°, respectively. The antagonist activity was greater at the initial and final stages of the movement. Three way analysis of variance designs indicated significant differences in the agonist and antagonistic activity of knee extensors and flexors between eccentric and concentric exercise. The results of this study demonstrate that, despite changes in magnitude, the moment-angle and IEMG activity-angle patterns of the agonists were not affected by angular velocity and muscle action conditions. On the contrary, the IEMG activity-angle curves of the antagonists during maximal isokinetic voluntary efforts are affected by angular velocity conditions but were independent of the type of muscle action examined.
Patellofemoral pain syndrome (PFPS) is one of the most prevalent musculoskeletal conditions of the lower limb. The muscle imbalance between the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles is one of the main factors leading to the development of PFPS. The disparity in research and the necessity to add to the existing literature base led to the development of this study. The aim of this study was to investigate the effect of 2 closed kinetic chain exercises and 1 open kinetic chain exercise on VMO and VL muscle activity. Twenty-two healthy asymptomatic individuals participated in this study. The surface electromyography (EMG) of VMO and VL was measured and used to calculate the VMO:VL ratio during 3 different quadriceps-strengthening exercises (a double leg squat with isometric hip adduction exercise, an open kinetic chain knee extension exercise, and a lunge exercise). The double leg squat with isometric hip adduction exercise was shown to produce a significantly greater VMO:VL ratio (1.14:1) than the other 2 exercises (p = 0.015 and p = 0.005). The open kinetic chain knee extension exercises produced significantly greater activation of VL than the lunge exercise (p = 0.001 and p = 0.036). The lunge exercise produced the VMO:VL ratio (1.18:1) closest to the idealized ratio of 1:1. Potential clinical recommendations can be made proposing the lunge exercise as a key tool in early rehabilitation when restoring preferential VMO:VL ratio is essential. The double leg squat with isometric hip adduction exercise would be useful in maintaining correct patella tracking and selectively strengthening VMO.
The purpose of this investigation was to examine the impact of training on the power-, force-, and velocity-time curves of the countermovement jump (CMJ) through both cross-sectional and longitudinal comparisons. The most novel aspect of this study was the analysis of these curves for the entire movement at a sampling frequency of 386-506 Hz averaged across 30 subjects. Thirty subjects, all men, participated in this investigation and included 12 athletes and 18 untrained men. Two major comparisons were conducted: 1) an acute, cross-sectional examination comparing experienced jumpers (jump height > 0.50 m; n = 12 men's athletes) with nonjumpers (jump height < 0.50 m; n = 14 untrained men), and 2) a longitudinal examination comparing performance before and after 12 weeks of power training (training group n = 10 untrained men; control group n = 8 untrained men). Data obtained from the baseline testing session of 14 subjects involved in the longitudinal study were used for the cross-sectional examination to represent the nonjumper group. The cross-sectional examination revealed significant (p <or= 0.05) differences between jumpers and nonjumpers in peak performance variables (i.e., peak power, force, velocity, displacement) as well as over a range of time points throughout the power-, force-, velocity-, and displacement-time curves of the CMJ. Similar results were observed in the longitudinal examination, with power training eliciting significant changes to peak performance variables as well as significant changes to the power-, force-, velocity-, and displacement-time curves over a range of time points throughout the CMJ. This study illustrates that training status not only influences the peak performance variables of the countermovement jump but also impacts the shape of the power-, force-, velocity-, and displacement-time curves throughout the movement. Because analysis of peak performance variables offers little insight into how adaptations have occurred after training, examination of the changes to the power-, force-, velocity-, and/or displacement-time curves offers a simple yet powerful monitoring technique that practitioners can use to gain insight into the precise nature and timing of adaptations to training.
Electromyography (EMG) is commonly used to determine the electrical activity of skeletal muscle during contraction. To date, independent verification of the relationship between muscle use and EMG has not been provided. It has recently been shown that relaxation- (e.g., T2) weighted magnetic resonance images (MRI) of skeletal muscle demonstrate exercise-induced contrast enhancement that is graded with exercise intensity. This study was conducted to test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise. Both MRI and EMG data were collected for separate eccentric (ECC) and concentric (CON) exercise of increasing intensity to take advantage of the fact that the rate of increase and amplitude of EMG activity are markedly greater for CON muscle actions. Seven subjects 30 +/- 2 (SE) yr old performed five sets of 10 CON or ECC arm curls with each of four resistances representing 40, 60, 80, and 100% of their 10 repetition maximum for CON curls. There was 1.5 min between sets and 30 min between bouts (5 sets of 10 actions at each relative resistance). Multiple echo, transaxial T2-weighted MR images (1.5 T, TR/TE 2,000/30) were collected from a 7-cm region in the middle of the arm before exercise and immediately after each bout. Surface EMG signals were collected from both heads of the biceps brachii and the long head of the triceps brachii muscles. CON and ECC actions resulted in increased integrated EMG (IEMG) and T2 values that were strongly related (r = 0.99, P < 0.05) with relative resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
1. Raw or rectified and integrated electromyograms (integrated EMGs) of the leg muscles were recorded during (a) isotonic ramp shortening or lengthening contractions consisting of foot plantar flexions against a constant load, or dorsal flexions accomplished by braking the load and yielding to it, respectively, and (b) isometric increasing or decreasing plantar torques accomplished by graded contractions or relaxations of the triceps muscles. 2. During plantar flexions or increasing torques, the EMG of soleus, gastrocnemius lateralis, medialis, and peroneus increased in parallel. During decreasing torques, motor unit derecruitment took place gradually and simultaneously. The tibialis anterior was silent. During dorsal flexions, one of two characteristic patterns was observed in different subjects: (a) soleus was abruptly derecruited at the beginning of the task, while gastrocnemius lateralis (or medialis) exhibited a large recruitment lasting throughout the lengthening contraction; (b) soleus remained active during the task, showing large motor unit potentials, while the gastrocnemius lateralis recruitment was of a lesser extent than in (a). Peroneus derecruitment was gradual and tibialis anterior activity was absent in both cases. 3. The EMG patterns observed during plantar flexions or in increasing and decreasing torques, and the two patterns observed during shortening or lengthening contractions, were closely reproduced during sinusoidal oscillations of the foot or in isometric contractions and relaxations. 4. When recruitment of the gastrocnemius lateralis was present during dorsal flexion, the slope of its integrated EMG envelope was steeper, the higher the velocity of lengthening contraction. The most rapid and the slowest tasks, however, did not require its activation. Gastrocnemius lateralis integrated EMGs of an amplitude similar to those occurring during lengthening contractions were observed only during ballistic plantar flexions. 5. The two patterns of triceps activation occurring during lengthening contraction could be traced to different mechanical characteristics of the soleus muscles, the gastrocnemius lateralis being activated preferentially in subjects with long soleus half-relaxation times, and the soleus in subjects with short soleus half-relaxation times. 6. The soleus and gastrocnemius lateralis H reflexes were tested during shortening and lengthening contractions.(ABSTRACT TRUNCATED AT 400 WORDS)
Movements that are performed with maximal velocity and acceleration can be considered ballistic actions. Ballistic actions are characterized by high firing rates, brief contraction times, and high rates of force development. A characteristic triphasic agonist/antagonist/agonist electromyographic (EMG) burst pattern occurs during ballistic movement, wherein the amount and intensity of antagonist coactivation is variable. In conditions of low-grade tonic muscular activity, a premovement EMG depression (PMD; or silent period, PMS) can occur in agonist muscles prior to ballistic contraction. The agonist PMD period may serve to potentiate the force and velocity of the following contraction. A selective activation of fast twitch motor units may occur in ballistic contractions under certain movement conditions. Finally, high-velocity ballistic training induces specific neuromuscular adaptations that occur as a function of the underlying neurophysiological mechanisms that subserve ballistic movement.
The purpose of this study was to examine the effect of isometric training of the quadriceps femoris muscles, at different joint angles, on torque production and electromyographic (EMG) activity.
One hundred seven women were randomly assigned to one of four groups. Three groups trained with isometric contractions three times per week at a knee flexion angle of 30, 60, or 90 degrees. The fourth group, which served as a control, did not exercise.
Isometric torque was measured using a dynamometer, and EMG activity was measured using a multichannel EMG system. Measurements were obtained during maximal isometric contraction of the quadriceps femoris muscles at 15-degree increments from 15 to 105 degrees of knee flexion. Measurements were taken before and after 8 weeks of training.
Following isometric exercise, increased torque and EMG activity occurred not only at the angle at which subjects exercised, but also at angles in the range of motion at which exercise did occur. Further analyses indicated that exercising in the lengthened position for the quadriceps femoris muscles (90 degrees of knee flexion) produced increased torque across all angles measured and appeared to be the more effective position for transferring strength and EMG activity to adjacent angles following isometric training as compared with the shorter positions of the muscle (30 degrees and 60 degrees of knee flexion).
These findings suggest that an efficient method for increasing isometric knee extension torque and EMG activity throughout the entire range of motion is to exercise with the quadriceps femoris muscles in the lengthened position.
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.
Surface EMG signals detected in dynamic conditions are affected by a number of artefacts. Among them geometrical factors play an important role. During movement the muscle slides with respect to the skin because of the variation of its length. Such a shift can considerably modify sEMG amplitude. The purpose of this work is to assess geometrical artefacts on sEMG during isometric contractions at different muscle lengths. The average rectified value (ARV) of 15 single differential signals was obtained by means of a linear array of 16 bar electrodes from the vastus medialis and lateralis muscles. The knee angle was changed from 75 degrees to 165 degrees in steps of 30 degrees and voluntary isometric contractions at a low, medium and high force level were performed for each angle. The ARV pattern was normalized with respect to the mean activity to compare signals from different joint angles. From the data collected it was possible to separate the geometrical changes from the changes due to different intensities of activation. In three out of five subjects, we found (within the resolution of our measures) a 1 cm shift for the vastus medialis muscle while no shift was observed for the other two subjects. For the vastus lateralis muscle a 1 cm shift was found in two out of four subjects. Such a shift produces the main contribution to geometrical artefacts. To avoid such artefacts the innervation zones should be located and the EMG electrodes should not be placed near them.
The concept that the endplate noise and endplate spike components of motor endplate potentials represent normal endplate potentials seems to be flawed. The morphology of the normal miniature endplate potentials described in the physiology literature is different from the morphology of the noise-like component of endplate potentials. This noise-like component is identified as normal in current electromyographic literature. There is strong experimental evidence that one source of the endplate noise component is grossly increased release (up to three orders of magnitude) of acetylcholine from the nerve terminal of that neuromuscular junction. The spikes can be accounted for by release of additional acetylcholine in response to mechanical stimulation by the electromyographic needle. Other possibilities exist.
It is the purpose of this article (a) to show the influence of electrode location on EMG amplitude and spectral variables for simulated and real signals for different muscles of the thigh and leg, (b) to investigate the relative movement of the muscle under the recording electrodes when the joint angle changes for the set of muscles most frequently investigated in gait analysis, and (c) to illustrate how different electrode locations may lead to different interpretations of the muscle activity investigated with amplitude and spectral analysis of the surface EMG signal. The study has been carried out on the following muscles of the leg and thigh: rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, tibialis anterior, gastrocnemius lateralis, and gastrocnemius medialis.
Many previous studies were focused on the influence of anatomical, physical, and detection-system parameters on recorded surface EMG signals. Most of them were conducted by simulations. Previous EMG models have been limited by simplifications which did not allow simulation of several aspects of the EMG generation and detection systems. We recently proposed a model for fast and accurate simulation of the surface EMG. It characterizes the volume conductor as a non-homogeneous and anisotropic medium, and allows simulation of EMG signals generated by finite-length fibers without approximation of the current-density source. The influence of thickness of the subcutaneous tissue layers, fiber inclination, fiber depth, electrode size and shape, spatial filter transfer function, interelectrode distance, length of the fibers on surface, single-fiber action-potential amplitude, frequency content, and estimated conduction velocity are investigated in this paper. Implications of the results on electrode positioning procedures, spatial filter design, and EMG signal interpretation are discussed.
Previous studies have suggested that regionalization may occur for human motor units, whereby smaller motor units are located in deeper parts of the muscle and larger motor units are located in more superficial portions. We examined this possibility in the human vastus lateralis muscle using macro-EMG (electromyography) to estimate motor unit size. The sample consisted of nine individuals from whom 114 motor units were recorded at forces ranging between 5% and 60% MVC. Peak-to-peak macro-EMG amplitude was well correlated with macro area (Spearman rho = 0.96). There was a statistically significant inverse relationship between recording depth and macro peak-to-peak amplitude (rho = -0.402, p < 0.001). We conclude that there is a nonrandom distribution of motor units in human muscle, with larger motor units located in more superficial regions and smaller units located in deeper regions. Clinicians who monitor motor unit activity need to recognize that a representative sample of motor unit recordings should include motor units from both deeper and more superficial regions of muscle.
Despite the functional importance of the human quadriceps femoris in movements such as running, jumping, lifting and climbing, and the known effects of muscle architecture on muscle function, no research has fully described the complex architecture of this muscle group. We used ultrasound imaging techniques to measure muscle thickness, fascicle angle and fascicle length at multiple regions of the four quadriceps muscles in vivo in 31 recreationally active, but non-strength-trained adult men and women. Our analyses revealed a reasonable similarity in the superficial quadriceps muscles, which is suggestive of functional similarity (at least during the uni-joint knee extension task) given that they act via a common tendon. The deep vastus intermedius (VI) is architecturally dissimilar and therefore probably serves a different function(s). Architecture varies significantly along the length of the superficial muscles, which has implications for the accuracy of models that assume a constant intramuscular architecture. It might also have consequences for the efficiency of intra- and intermuscular force transmission. Our results provide some evidence that subjects with a given architecture of one superficial muscle, relative to the rest of the subject sample, also have a similar architecture in other superficial muscles. However, this is not necessarily true for vastus lateralis (VL), and was not the case for VI. Therefore, the relative architecture of one muscle cannot confidently be used to estimate the relative architecture of another. To confirm this, we calculated a value of whole quadriceps architecture by four different methods. Regardless of the method used, we found that the absolute or relative architecture of one muscle could not be used as an indicator of whole quadriceps architecture, although vastus medialis, possibly in concert with VL and the anterior portion of VI, could be used to provide a useful snapshot. Importantly, our estimates of whole quadriceps architecture show a gender difference in whole quadriceps muscle thickness, and that muscle thickness is positively correlated with fascicle angle whereas fascicle length is negatively, although weakly, correlated with fascicle angle. These results are supportive of the validity of estimates of whole quadriceps architecture. These data are interpreted with respect to their implications for neural control strategies, region-specific adaptations in muscle size in response to training, and gender-dependent differences in the response to exercise training.
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