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Prediction of Knee Extensor and Flexor Isokinetic Strength in Young Male Soccer Players
Abstract
Single group, cross-sectional study.
To measure various anthropometric and demographic variables in young male soccer players and to use these measurements to develop equations with which to predict the isokinetic, concentric, and eccentric moment of force.
The development of equations that can predict isokinetic muscle strength from commonly measured subject characteristics can assist in the effective design of training and rehabilitation programs for athletic children.
One hundred thirteen male soccer players (13.50 +/- 2.21 years of age) performed eccentric and concentric maximum efforts of the knee extensors and flexors at 60, 120, and 180 degrees/second. Stepwise regression tests were used to develop predictive equations using combinations of age, height, body mass, sexual maturation (Tanner) stage, percentage of body fat, and hours spent training per week.
The results indicated a significant relationship of concentric and eccentric isokinetic strength for both knee extensors and flexors with 73-93% of the variance explained by using combinations of age, body mass, percentage of body fat, and hours training per week. Body mass and age were the main predictor variables under concentric conditions, whereas chronological age was not included in the models under eccentric conditions.
The relation between isokinetic moment and multiple anthropometric and demographic variables depends on the type of muscle action examined. The results suggest that the equations we developed can be used to predict the isokinetic moment in trained, young soccer players. A cross-validation analysis is required to confirm the accuracy and the suitability of the equations developed in our study.
... Furthermore, little is known about the relationships between the strength increase and factors such as physiological age, which is probably an important explanatory factor in the high observed variability of the development in stature, morphology, strength and physical abilities [14,15]. Only one study (by Kellis et al. [13]) has reported correlations between muscle strength, chronological age and certain morphological characteristics (height, weight and body mass index [BMI]). Moreover, it has been reported that high-intensity physical activity can modify the development of puberty [11]. ...
... Our results show that bodyweight is the variable which correlates most strongly with the various peak torque values, as reported by Gross et al. [9] in 134 healthy volunteers aged between 10 and 80. Our results also agree with those reported by Kellis et al. [13], who found an even more strongly significant relationship for concentric and eccentric isokinetic strength for both knee extensors and flexors. Between 73% and 93% of the variance were explained by combinations of age, body mass, percentage of body fat and hours spent training per week. ...
... En outre, on ne retrouve que peu de travaux sur les relations entre l'augmentation de la force et des facteurs tels que l'a ˆge physiologique, qui est probablement un facteur explicatif important dans la variabilité e ´levée observée de l'e ´volution de la stature, la morphologie, la force et les capacités physiques [14,15]. Une seule e ´tude (réalisée par Kellis et al. [13]) a rapporté des corrélations entre la force musculaire, l'a ˆge chronologique et de certaines caractéristiques morphologiques (taille, poids et l'indice de masse corporelle [IMC]). En outre, il a e ´té retrouvé qu'une activité physique très intense pouvait modifier le développement de la puberté [11]. ...
To investigate the relationships between isokinetic knee flexor and extensor muscle strength and physiological and chronological age in young soccer players.
Seventy-nine young, healthy, male soccer players (mean+/-standard deviation age: 12.78+/-2.88, range: 11 to 15) underwent a clinical examination (age, weight, height, body mass index and Tanner puberty stage) and an evaluation of bilateral knee flexor and extensor muscle strength on an isokinetic dynamometer. Participation in the study was voluntary.
The peak torque increased progressively (by 50%) between the ages of 11 and 15 and most significantly between 12 to 14. The knee flexor/extensor ratios only decreased significantly between 14 and 15 years of age. Puberty stage was the most important determinant of the peak torque level (ahead of chronological age, weight and height) for all angular velocities (p<0.0001). Muscle strength increased significantly between Tanner stages 1 and 5, with the greatest increase between stages 2 and 4.
The present study showed that isokinetic muscle strength increases most between 12 and 13 years of age and between Tanner stages 2 and 3. There was strong correlation between muscle strength and physiological age.
... Furthermore, strength levels of the unaffected limb frequently represent a reference value against which restoration of strength of the affected limb. Evidence on bilateral leg differences in soccer players is unclear as some studies have reported no differences [107] whereas others reported a 10% difference in both Q and H strength in favor of the non-dominant leg [108] . Others, however, have shown that bilateral leg differences exist only in the hamstrings but not in the quadriceps (players displayed weaker hamstrings in the dominant leg than the non-dominant one) [109,110] . ...
... Furthermore, during puberty strength improvement of the knee flexors is diverged from the extensors, particularly for the females [121] . Although in males the hamstrings and quadriceps isokinetic peak torque increases proportionally during growth [107,121] , in females the peak torque of hamstrings does not follow the improvement achieved in quadriceps [121] . This deficit in knee flexion torque observed in females results in a decreased torque H:Q ratio. ...
Although injury and neuromuscular activation patterns may be common for all individuals, there are certain factors which differentiate neuromuscular activity responses between children, adults and elderly. The purpose of this study is to review recent evidence on age differences in neural activation and muscle balances around the knee when performing single joint movements. Particularly, current evidence indicates that there are some interesting similarities in the neuromuscular mechanisms by which children or the elderly differ compared with adults. Both children and elderly display a lower absolute muscle strength capacity than adults which cannot fully be explained by differences in muscle mass. Quadriceps activation failure is a common symptom of all knee injuries, irrespective of age but it is likely that its effect is more evident in children or adults. While one might expect that antagonist co-activation would differ between age categories, it appears that this is not the case. Although hamstring: quadriceps ratio levels are altered after knee injury, it is not clear whether this is an age specific response. Finally, evidence suggests that both children and the elderly display less stiffness of the quadriceps muscle-tendon unit than adults which affects their knee joint function.
... The greater absolute peak torque values may be attributed to the greater body mass values of the basketball players compared to soccer players. The results of this study and those of Erdemir et al. [32] support the findings of previous studies, which reported that body mass has a significant effect on peak torque values of knee extensor and flexor muscles [45]. In the same context, Housh et al. [46] compared the age-related increases in muscle strength with changes in body mass and fat free mass in young wrestlers and commented that the strength increases cannot be attributed only to changes in body mass. ...
The present study examined and compared the isokinetic peak torque and the reciprocal ratios of the knee joint between young basketball and soccer players. An amount of 100 soccer and 100 basketball players took part in this study and were separated into five equal groups (n = 20), according to their chronological age (12, 13, 14, 15, and 16 years old). The absolute concentric (CON) and eccentric (ECC) peak torque of the knee flexor and extensor muscles (at 60°/s, 180°/s) were assessed using a Cybex Norm dynamometer, and the relative peak torque (per unit of body mass), as well as the conventional (CON/CON; ECC/ECC) and functional (CON/ECC; ECC/CON) ratios, were calculated. Data analysis indicated that the basketball players had higher absolute peak torque values than the soccer players throughout their developmental ages (p < 0.05). When the isokinetic peak torque values were normalized relative to body mass, no differences were observed between basketball and soccer players in any age group (p > 0.05). Additionally, no differences were observed in conventional and functional ratios between soccer and basketball players (p > 0.05). In conclusion, it appears that, during developmental ages (12–16 years old), the isokinetic strength profile (independent of body mass affecting absolute values) of knee extensor and flexor muscles develops similarly in basketball and soccer players.
... Our data was according to previous data reported for male soccer players. Kellis et al. (2000) demonstrated that body mass and age were strongly associated with concentric isokinetic thigh muscles strength, and they are the main predictor variables for concentric isokinetic strength. Between U15 and U18, there were no significant difference in weight and height values, then this may be the reason for the lack of isokinetic muscular strength difference. ...
The aim of this study was to evaluate and compare the hamstring (H) and quadriceps (Q) strength, bilateral difference and balance ratios in female soccer players. Ninety-three athletes from three age groups: under 13 (U13), 15 (U15) and 18 (U18) participated in the study performing isokinetic tests to measure peak torque, total work, average power and torque at 30º of thigh muscles. Conventional strength balance ratios, angle-specific balance ratio and bilateral strength difference were evaluated. There was bilateral strength difference for extensor muscles total work (p = 0.02) in U13 and flexor muscles peak torque (p = 0.02) in U15. All variables were superior in U15 than U13 (p <.05). There was no strength difference between U15 and U18. Balance ratios did not differ between sides or age groups. The study showed that although peak torque values were higher in U15 than in U13, balance ratios were similar.
... The asymmetry in strength of reciprocal © Editorial Committee of Journal of Human Kinetics muscle groups may increase the risk for muscle injury (Kellis et al., 2000;Thorborg et al., 2010Thorborg et al., , 2011a. The abduction-to-adduction (Sugimoto et al., 2014) torque ratios are used in sports medicine to monitor potential groin-and hip-related injuries, and to assess the strength profile of the hip joint. ...
The main objective of this study was to provide an extensive isokinetic profile of the hip joint in youth soccer players, where the literature is limited. Additionally, this study investigated the effect of age on isokinetic peak torque values of hip abductor and adductor muscles and on reciprocal muscle group torque ratios in youth soccer players at different angular velocities (30 vs. 90o/s) and muscle actions (concentric vs. eccentric). Sixty young elite male soccer players were assigned into three equal groups (n = 20): children, young adolescents and older adolescents, and performed five maximal concentric and eccentric hip-abductions and adductions at 30o/s and 90o/s. The results showed a significant increase (p < 0.05) in peak torque values from childhood to adolescence, with the exception of young adolescents vs. older adolescents where no differences were observed. The reciprocal ratios were not affected by age, but improved with an increase in angular velocity with the exception of the CON/ECC ratio that was higher at 30o/s. The data presented in this study provide an extensive isokinetic profile of hip abductor and adductor muscle strength in youth soccer players to assist both coaches and sports medicine professionals in strength monitoring and training.
... To monitor for a multicollinearity effect, the variance inflation factor (VIF) was calculated. A model was considered ill-conditioned if the VIF was higher than 10. 16 The threshold for statistical significance was when p < 0.05. ...
This study aimed to examine the relationship between the morphological and mechanical properties of the muscle‐tendon unit and sprint time in prepubescent sprinters. Fifteen prepubescent sprinters participated in this study; the average personal best time in a 100 m race was 14.00 ± 0.68 sec. The stiffness of the tendon structure was measured using ultrasonography during isometric contraction; the muscle thickness of the vastus lateralis (VL) and the medial gastrocnemius (MG) were also measured. There was a significant negative correlation between tendon structure stiffness of the plantar flexors and 100 m personal best time (r = ‐0.58, p < 0.05), but not the knee extensors. Unlike for the MG, the muscle thickness of the VL (r = ‐0.61, p < 0.05) and the 100 m personal best time were significantly negatively correlated. Stepwise regression analysis identified the tendon structure stiffness of the plantar flexors and the muscle thickness of the VL as independent variables, which were significantly associated with the 100 m personal best time (r = 0.77, p < 0.01). These results suggest that in prepubescent sprinters, superior sprint performance is induced by a stiff tendon structure of the plantar flexors and a greater muscle thickness of the VL.
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... The interpretation of an isokinetic test should be made in the context of what is expected for a given individual's age, weight, height, and physical activity level, if no apparent limiting condition is present [21][22][23]. Several studies have provided reference equations for knee extensor isokinetic strength norms, all of which focussed young and middle aged adults, and thus with limited number of older subjects included in their samples [20,21,[24][25][26]. Two of the most widely known reference equations developed by Neder et al. [20] and Gross et al. [24] were derived from a sample of men and women with a wide age range (from 10 to 84 years). ...
Background
Knee extensor strength assessment has been especially emphasized in older people, but lack of reference values limits its usefulness in geriatric evaluation.
Aims
The aim of this study was to develop a reference equation for knee extensor isokinetic strength standards in older women.
Methods
Knee extensor isokinetic tests at 60°/s were performed in 390 Brazilian older women aged 60–84 years (67.38 ± 5.56 years) and in a separate validation sample of 110 women (67.94 ± 6.13 years). A regression equation for peak torque (PT) was derived and compared to commonly used formulas: the equations of Neder and Gross. Age, weight and height were the only significant predictors (multiple R = 0.55; R² = 0.30; p < 0.001). The proposed equation was examined in the independent sample. Percent from predicted values was calculated and Bland–Altman plots were constructed.
Results
Both the Neder and Gross equations significantly underestimated predicted PT values (both p < 0.001); mean bias were 6.79 and 6.75, respectively. The proposed equation [PT = 39.72 − (1.24 × age) + (0.44 × weight) + (69.70 × height)] was matched with the independent sample, with a percent predicted isokinetic strength of approximately 95%, a mean bias approximately 40% lower 4.23 than the other equations, and stable across all age groups.
Conclusions
Available equations for knee extensor isokinetic strength are not adequate for older women. The equation developed in the present study provided considerably lower average error and thus with more suitable reference values.
... 발목관절의 주동근과 길항근의 균형과 협응이 요구되므 로, 두 근육 사이의 최대우력 비율을 파악하는 것이 필 요하다. 무릎과 발목의 최대우력(maximal force)을 알 아보기 위한 근력평가로 등속성, 등장성, 그리고 등척성 방법이 이용되는데, 이 중 등속성 평가방법의 장점은, 일정한 각속도의 관절가동범위를 통해 발생되는 근력을 정확하게 측정할 수 있으며 신뢰성 또한 높다는 것이다 (Kellis 등, 2000; Neder 등, 1999; Sole 등, 2007). ...
In dancers, intact muscular coordination is a well balanced antagonist, which could be a decisive factor in protection against injury as dancers often have hypermobile joints and their ankle joints often bear their full body weight in extreme positions. The purposes of this study were to identify the isokinetic strength to the knee and ankle and the isometric strength of the trunk in female collegiate dancers and controls. Furthermore, the study aimed to investigate the peak torque ratio of knee extension to flexion, ankle plantarflexion (PF) to dorsiflexion (DF), and dominant legs to nondominant. Twenty-one female collegiate dancers (20.0 years of age) and twenty-one female collegiate students (19.3 years of age) performed isokinetic maximum efforts of the knee extensors and flexors at and , the ankle plantarflexors and dorsiflexors at and and isometric maximum efforts of the lumbar extensors at , , , , , , and . The results were as follows: The isokinetic peak torque of the knee extensors and the ratio of knee extensors to flexors of dancers were significantly higher than those of controls (p
... Although various studies [20][21][22] showed that age, biological maturity, number of years of training, morphology and anthropometry affect the physical and physiological profile of players, few studies have investigated on the relationship among this variables in youth soccer players. Understanding the correlation between physical and physiological demands of youth soccer players could have practical implications for training prescription, talent identification and the quantification of training loads. ...
Purpose
Changes in body size and functional capacities are highly individual during puberty, and the performance of a soccer player is often closely related to their maturity status. The aim of the study was to evaluate the relationships among explosive power, body fat, fat free mass and pubertal development in young soccer players.
Methods
Explosive power (countermovement jump—CMJ), body mass index (BMI), percentage of body fat (%BF), fat free mass (FFM) and a Self-Administered Rating Scale for pubertal development (PDS) values of 11 “Giovanissimi” (age 13 year), 13 “Allievi” (age 15 year) and 10 “Juniores” (age >17 year) male soccer players were compared. The statistical analysis was performed using an analysis of variance among categories with Fisher’s post hoc as appropriate. Furthermore, Pearson correlations among variables were calculated considering all subjects and also within categories.
Results
Statistical differences emerged among categories in CMJ (F (2,30) = 28.3, p < 0.01), body fat weight (F (2,31) = 29.2, p < 0.01) and PDS (F (2,29) = 18.5, p < 0.01), while %BF values showed statistical differences only for “Giovanissimi” and “Juniores” (F (2,31) = 3.4, p = 0.01). CMJ showed significant correlations with FFM (r = 0.68) and PDS (r = 0.63), PDS with FFM (r = 0.66) and BMI with %BF (r = 0.71) and FFM (r = 0.71). A high correlation was found within categories.
Conclusion
Since we found differences between categories and no correlation between chronological age and pubertal status, this study highlights the importance of assessing of puberty in youth soccer team.
... Le potentiel musculaire évoluant avec l'âge [3,5,15,32,36,41], il est intéressant de quantifier ces adaptations et de définir, à classe d'âge égale, l'influence d'une pratique sportive. Si de nombreuses études ont évalué les capacités musculaires de footballeurs [6,9,16,23,35], très peu se sont intéressées aux gymnastes mâles [11,40] ou à la comparaison de ces deux types de populations. Le football sollicite intensément les membres inférieurs [8,10,48]. ...
OBJECTIVE: The aim of this work is the assessment of age and sport influences on the isokinetic knee muscle characteristics.SUBJECTS AND METHOD: Subjects performed a bilateral knee flexion/extension test on an isokinetic device at 60 and 180°.s–1 speed in concentric mode. The three parameters studied in this work were the Peak Torque, Average Power and hamstring/quadriceps ratio. Thirty-eight soccer players (16,6 〚± 1.4〛 years old) and 22 gymnasts (18 〚± 2.8〛 years old) were tested. The population was separated into three groups : 15 years old, 17 years old, 20 years old.RESULTS: The isokinetic values of soccer players were significantly higher (p
... New normative values of vertical jumping parameters and leg power could be used by physical educators to distinguish subjects of different levels of performance (7,29), by coaches to monitor effectiveness of athletic training procedures (23) and by researchers to identify both the determining factors and trainability of strength and power during childhood (4). The literature contains few studies about the muscle power of athletic children (6,15), especially according to the ethnic group. Buchanan and Vardaxis (7) showed that height and weight are important predictors of muscle strength in young basketball players. ...
The purpose of this study was to examine the relative contributions of anthropometric variables to vertical jumping ability and leg power and to establish reference values of vertical jumping parameters in athletic Tunisian children aged 7-13 years in both sexes. Three hundred and ninety-one athletic Tunisian children (208 boys and 183 girls) aged 7-13 years were randomly selected to participate in our study. They were asked to perform squat jumps and countermovement jumps. Jump heights and leg power were simultaneously provided by the optojump device. Full and stepwise regression models were calculated to identify which anthropometric parameters significantly contributed to performance variables. The multiple regressions showed that age, weight, standing height and fat-free mass were the predictors of jumping performance. The results may help in verifying the effectiveness of a specific training program and detecting highly talented athletes.
... Data from prospective and retrospective cohort studies sustained that physically active children have higher bone mineral density (BMD) than sedentary controls [1] and sports practice has been reported to have a great developing impact during growth, both in BMD [2] and strength [3]. ...
To analyse the relationship between isokinetic strength of the lower limb muscles and bone mineral density and content (BMD, BMC) of adolescent male soccer players and age-matched controls not involved in sport (12-15 years).
A random sample of 151 young males was divided into soccer players (SG; n=117) and control subjects (CG; n=34). Peak torque of knee extensors (PTE) and flexors (PTF) was measured during isokinetic knee joint movement (90°/s) of the dominant and non-dominant lower limbs. BMD and BMC of the whole-body, lumbar spine, dominant/non-dominant lower limb were determined by dual-energy X-ray absorptiometry. Physical activity was monitored with accelerometers during 5 days. Estimated maturity offset was used as an indicator of biological maturity status.
Whole-body BMD (1.03±0.01 vs. 0.98±0.01 g/cm2, P=0.003) and dominant (1.09±0.01 vs. 1.02±0.01 g/cm2, P<0.001) and non-dominant (1.09±0.01 vs. 1.01±0.01 g/cm2, P<0.001) lower limb BMD was greater in SG compared to CG. No significant differences were found for BMC. Compared to CG, SG performed better in the YY-IE2 test (780±40 vs. 625±31 m), exhibited higher PTE (dominant limb: 155.2±30.3 vs. 123.4±37.0N m; non-dominant limb: 156.2±36.1 vs. 120.4±41.1 N m) and PTF muscles (dominant limb: 79.0±25.3 vs. 57.1±25.3 Nm; non-dominant limb: 73.3±20.7 vs. 57.0±24.2N m). Moreover, the PTE, soccer participation and maturity status were positively associated with the BMD at all body sites (r2=0.57-0.73, P<0.05).
Muscle strength of knee extensors is associated with BMD and BMC at all body sites. Muscle-skeletal structures respond positively to the weight-bearing and impact-loading imposed by soccer practice. Soccer seemed to be a multilateral balanced sport activity.
... To monitor for a multicollinearity effect, the variance inflation factor (VIF) was calculated. A model was considered ill conditioned if the VIF was higher than 10 ( Kellis et al. 2000). Statistical significance was defined as P ˂ 0.05. ...
Enhanced echo intensity (EI) on an ultrasound image of skeletal muscle indicates changes in muscle quality, including increases in intramuscular fibrous and adipose tissues. However, it is not known whether muscle quality assessed from the EI of computer-aided gray-scale analysis of an ultrasound image is associated with the muscle strength or body composition of a subject. The objectives of this study were to investigate whether muscle quality assessed from EI measured using gray-scale analysis is associated with muscle strength independently of age or muscle thickness (MT), and to examine the relationship between muscle EI and body composition. Ninety-two healthy women with a mean age of 70.4 ± 5.5 years (range, 51-87 years) dwelling in Kyoto, Japan, participated in the study. The MT, subcutaneous fat thickness (FT), and EI of the quadriceps femoris on the right extremity were assessed from transverse ultrasound images. Knee extensor isometric strength was used as a measure of the quadriceps femoris muscle strength. EI was significantly correlated with quadriceps strength independently of age or MT, and stepwise regression analysis revealed that MT and EI were independently associated with quadriceps strength. Importantly, EI showed no significant correlations with FT, percentage of body fat (%BF), or body mass index (BMI), while FT, BMI, and %BF did not significantly influence muscle strength. These data suggest that muscle quantity (i.e., MT) and muscle quality assessed from EI measured using computer-aided gray-scale analysis independently contribute to muscle strength in middle-aged and elderly persons.
... For example, it may be postulated that isoinertial eccentric strength assessment is not suitable for children and the elderly, given that maximal eccentric contraction requires external load greater than a MVIC or 1RM (6,34). Children and elderly populations have been tested eccentrically on isokinetic devices (25,29) but never in an isoinertial context. With eccentrics, there are often problems related to control of speed, standardization of the movement and ability to apply a high enough load simply and safely (17). ...
Eccentric strength is an important component of functional daily activity and athletic performance; therefore, assessing this capability is important. Typically, isokinetic dynamometers are used to assess eccentric force capability. However, because of the limitations associated with the contraction mode (i.e., constant velocity), limited information can be obtained concerning functional muscle performance from this form of assessment. Consequently, the isoinertial assessment of eccentric force may provide more useful information for strength and conditioning practitioners. This article reviews what little research there is in this area, discussing the methodologies and limitations of the assessments used to quantify eccentric force capability.
The circulatory level of pentraxin3 (PTX3), an anti-inflammatory cardio-protective protein, has been known to be lower in obese individuals than in those with normal weight. However, reports on the effects of different weight-loss methods on PTX3 were limited. The present study aimed to investigate the effect of weight loss on the circulating PTX3 levels in overweight and obese men and to examine the combined effect of dietary modification and exercise training on PTX3 levels. Forty-eight overweight and obese men were assigned to two groups: the dietary modification (group D) or exercise training and dietary modification (group DE). Groups D and DE were composed of 27 and 21 participants, respectively. We observed a significant independent relationship between the changes of PTX3 and body mass index (BMI) in all participants (β=-0.617, p<0.01). Subsequently, we compared the effect of two other types of weight loss on plasma PTX3 in groups D and DE. The magnitude of increase in plasma PTX3 levels was similar in the two groups. Interestingly, we observed that PTX3 levels in group DE increased significantly more than those in group D in subjects who achieved normal weight, as defined based on BMI, after interventions. Our present study suggested that weight reduction after lifestyle modification significantly increased PTX3 levels in overweight and obese men, and the addition of habitual exercise to dietary modification enhanced the magnitude of increasing of PTX3 levels in obese individuals achieving normal weight after weight loss.
The applied use of eccentric muscle actions for physical rehabilitation may utilize the framework of periodization. This approach may facilitate the safe introduction of eccentric exercise and appropriate management of the workload progression. The purpose of this data-driven Hypothesis and Theory paper is to present a periodization model for isokinetic eccentric strengthening of older adults in an outpatient rehabilitation setting. Exemplar and group data are used to describe the initial eccentric exercise prescription, structured familiarization procedures, workload progression algorithm, and feasibility of the exercise regimen. Twenty-four men (61.8 ± 6.3 years of age) completed a 12-week isokinetic eccentric strengthening regimen involving the knee extensors. Feasibility and safety of the regimen was evaluated using serial visual analog scale (VAS, 0–10) values for self-reported pain, and examining changes in the magnitude of mean eccentric power as a function of movement velocity. Motor learning associated with the familiarization sessions was characterized through torque-time curve analysis. Total work was analyzed to identify relative training plateaus or diminished exercise capacity during the progressive phase of the macrocycle. Variability in the mean repetition interval decreased from 68 to 12% during the familiarization phase of the macrocycle. The mean VAS values were 2.9 ± 2.7 at the start of the regimen and 2.6 ± 2.9 following 12 weeks of eccentric strength training. During the progressive phase of the macrocycle, exercise workload increased from 70% of the estimated eccentric peak torque to 141% and total work increased by 185% during this training phase. The slope of the total work performed across the progressive phase of the macrocycle ranged from −5.5 to 29.6, with the lowest slope values occurring during microcycles 8 and 11. Also, mean power generation increased by 25% when eccentric isokinetic velocity increased from 60 to 90° s⁻¹ while maintaining the same workload target. The periodization model used in this study for eccentric exercise familiarization and workload progression was feasible and safe to implement within an outpatient rehabilitation setting. Cyclic implementation of higher eccentric movement velocities, and the addition of active recovery periods, are featured in the proposed theoretical periodization model for isokinetic eccentric strengthening.
Purpose: The purpose of the study was to compare body composition and isokinetic strength of the hamstring and quadriceps muscles at 60°/sec and 180°/sec in healthy subjects and elite male soccer players during the pre-season period. Material and methods: 20 elite soccer players (SP) and 20 university male students (healthy subjects) were included in the study. The subjects were tested for peak torque (PT) (Nm), total work (J), and concentric hamstrings/quadriceps (H:Q) ratio of both knees at 60°/sec and 180°/sec on a Cybex 350 isokinetic dynamometer. Body composition was also assessed by skinfold measurements in the study. Fat-free mass (kg), fat mass (kg) and percentage of body fat were determined according to the Jackson and Pollach equation. Results: The concentric H:Q ratios for the left knee were significantly higher in soccer piayers than in the healthy subjects at angular velocities of 180°/sec (p=0.01). Soccer players had significantly higher fat-free mass, fat mass and percentage of body fat compared to healthy subjects (p<0.05). Conclusion: Based on these findings, we conclude that the mean H:Q ratios of elite soccer players were not in accordance with the literature.
Dance movements consist of combinations of movements such as jumping, rotation, maintaining balance, leg lifts, and plantar flexion with toe shoes. Dance movements require great muscle strength of lower extremities as well as muscular endurance. The purposes of this study were to investigate correlation between the anthropometric variables and the peak torque in young female dancers and to identify variables that affect isokinetic peak torque. Twenty-six female dancers ( years of age) performed concentric maximum force efforts on the knee extensors and flexors at and , the ankle plantar flexors (PF) and dorsiflexors (DF) at and . Antropometric variables such as age, height, weight, body mass index (BMI), thigh girth, calf girth and duration of dance training were measured. To identify antropometric variables related to muscle strength, Pearson correlations were computed and a stepwise multiple regression analysis was performed. Pearson correlation coefficients of Knee extensor at and revealed moderate positive associations with BMI and thigh girth. Pearson correlation coefficients of ankle PF revealed low-to-moderate positive associations with height. Ankle DF also revealed moderate positive associations with BMI and calf girth. The main predictor variables of knee extensor at 60/sec, were stepwise multiple regression, age, height, thigh and girth.
Controlled laboratory study.
To compare the changes in lower limb sagittal kinematics in running after a knee fatigue protocol with those observed after an ankle fatigue protocol.
Impaired force-generating ability of specific muscles may affect running mechanics, with negative implications for injury occurrence and performance. Identifying the strategies used to compensate for fatigue of selected muscles may assist in the design of more effective exercise programs for injury prevention and performance enhancement in running.
Sagittal plane kinematic data and the electromyographic (EMG) signal of the vastus medialis (VM), gastrocnemius (GAS), and biceps femoris (BF) muscles were collected from 15 females running at 3.61 m/s on a treadmill prior to, and following, an isokinetic knee extension/flexion and, on a separate day, an ankle plantar flexion/dorsiflexion fatigue protocol performed at 120 degrees/s.
Ankle muscle fatigue caused decreased ankle dorsiflexion, while knee fatigue caused increased knee flexion at initial contact (P<.05). Both protocols increased knee flexion angle at toe-off, as well as the amplitude of GAS and VM EMG signal, with the hip more extended after knee fatigue and the ankle more plantar flexed after ankle muscle fatigue. Ankle muscle fatigue caused a significant increase in hip extensionand ankle plantar flexion angular velocity, and a decline of BF EMG signal during the swing phase (P<.05). Knee muscle fatigue decreased hip and knee flexion angular velocity and increased BF EMG signal during the swing phase (P<.05).
Localized muscle fatigue effects on sagittal kinematics differed between the 2 protocols. However, the strategy used to compensate for fatigue was similar for both protocols: to protect the joints at initial impact and to prevent impairments in performance during toeoff and swing phase.
The purpose of this study was to develop a regression equation to predict back extensor maximal voluntary contraction (back strength) for females based on several anthropometric and strength measurements using a multiple regression technique.
Back strength is an important parameter in low back pain studies. However, the measurement of back strength is problematic in certain populations such as low back pain patients and pregnant women.
Back strength was measured as both moment at L4/L5 and force. Ten anthropometric or strength measurements were chosen to develop the prediction equation. The data used for developing the models were from eighty non-pregnant female subjects, age 18-42 and with no history of back pain in the past year. Backwards stepwise analysis was performed in order to choose the best fit predictors. The predictive ability of each of the models was checked using the cross-validation technique on 20 other subjects.
Two prediction models were developed for moment and force, respectively. The models explained 46.9% and 48.2% of the variance in back strength. No multicollinearity problem was found. The validation study showed that the observed back strength was highly correlated with the predicted back strength.
Mass, height, trunk length, grip strength and quadriceps strength are the best predictors of back strength in this study. The models developed in this study can be used for both general female low back pain patients and the pregnancy population.
The purpose of this study was to standardize an isokinetic testing protocol for quadriceps and hamstrings in children who are typically developing and are six through 13 years of age, to establish percentile charts of isokinetic peak torque strength for quadriceps and hamstrings by gender and age, and to determine the best predictors of strength for each of three testing speeds.
A total of 3587 children were tested for isokinetic knee strength according to our protocol on Biodex System II and III isokinetic dynamometers. Therapists participating in the study were trained on the protocol and inter-rater reliability was established. Both dominant and nondominant legs were tested at three speeds. Data were collected on peak torque, time to peak torque, and agonist/antagonist ratio. Data were also gathered on maturation level, gender, height, weight, leg length, laterality, and activity level to allow for investigation of correlations with peak torque. All data were entered in an Excel spreadsheet.
Percentile charts of normal isokinetic muscle strength were generated using SPSS 12.0 for each age and gender at three speeds (60, 120, and 180 degrees per second). Stepwise regression analysis determined height to be the best predictor of peak torque for both quadriceps and hamstrings at all speeds.
This study is the first to report normative peak torque values for quadriceps and hamstrings in children. By using a standardized testing protocol and normative data, clinicians will be able to assess the degree of muscle weakness as well as the effectiveness of intervention strategies.
The purpose of this study was to investigate the relationship between isokinetic strength knee testing and soccer kick kinematics using electromyography (EMG).
Thirteen pubertal soccer players (age: 14.3+/-0.4 years) performed maximum instep soccer kicks, while knee angular position of the swinging leg was recorded using a twin-axis electrogoniometer. Bipolar surface EMG activity of the vastus medialis, vastus lateralis and biceps femoris (BF) muscles was recorded. The subjects also performed maximum knee extension and flexion efforts at concentric angular velocities of 1.04, 3.14 and 5.23 rad x s(-1) and eccentric angular velocities of 1.04 and 3.14 rad x s(-1).
The correlation coefficients between isokinetic moments and knee angular velocity values during the kick ranged from 0.609 to 0.898 for concentric moments and from 0.431 to 0.612 for eccentric moments. Agonist EMG values during isokinetic tests ranged from 63.17+/-19.9% to 128.7+/-34.9% maximum voluntary contraction (MVC). Antagonist EMG levels ranged from 9.76+/-6.12% to 36.91+/-22.81% MVC. The corresponding EMG values during the soccer kick ranged from 12.78+/-6.8% to 122.34+/-61.5% MVC and increased as the foot approached the ball.
Isokinetic tests at intermediate and fast angular velocities are adequate for monitoring strength training programs in soccer. However, muscle activation patterns differ between the two movements, especially those of the BF muscle.
The reliable examination of isokinetic parameters in young athletes is important for the establishment of appropriate strength testing protocols. The purpose of this study was to examine the reliability of peak moments, non-preferred/preferred leg and reciprocal ratios during isokinetic knee efforts in young soccer players. Thirteen circumpubertal (age = 13.0 ± 0.4 years) soccer players performed maximum knee extension and flexion efforts at 30, 120 and 180°· s-1 in two occasions, a week apart. The reliability of the peak moments was high, with reliability coefficients ranging from 0.71 to 0.98. The nonpreferred/preferred leg and reciprocal ratios demonstrated moderate to high reliability (coefficients ranged from 0.42 to 0.87). The reliable examination of moments of force and ratio measurements during eccentric tests and at fast angular velocities in young soccer players requires extensive familiarization of the subjects prior to the main test.
Eccentric contractions occur when activated muscles are forcibly lengthened. This mode of muscle function occurs frequently in the activities of daily living and in athletic competition. This review examines the experimental evidence that provides the foundation for our current understanding of the benefits, consequences, and control of eccentric contractions. Over the past several decades, numerous studies have established that eccentric contractions can maximize the force exerted and the work performed by muscle; that they are associated with a greater mechanical efficiency; that they can attenuate the mechanical effects of impact forces; and that they enhance the tissue damage associated with exercise. More recent evidence adds a new feature to this repertoire by suggesting a new hypothesis: that the neural commands controlling eccentric contractions are unique. Examination of this hypothesis is critical because the existence of such a control scheme would increase substantially the complexity of the strategies that the nervous system must use to control movement.
The purpose of the present study was to examine age-related changes in isokinetic leg flexion and extension peak torque (PT), PT/body weight (PT/ BW), and PT/fat-free weight (PT/FFW) in young wrestlers. Male wrestlers (N = 108; age M ± SD = 11.3 ± 1.5 years) volunteered to be measured for peak torque at 30, 180, and 300° · s-1. In addition, underwater weighing was performed to determine body composition characteristics. The sample was divided into six age groups (8.1-8.9, n = 10; 9.0-9.9, n = 11; 10.0-10.9, n = 25; 11.0-11.9, n = 22; 12.0-12.9, n = 28; 13.0-13.9, n = 12), and repeated measures ANOVAs with Tukey post hoc comparisons showed increases across age for PT, PT/BW, and PT/FFW. The results of this study indicated that there were age-related increases in peak torque that could not be accounted for by changes in BW or FFW. It is possible that either an increase in muscle mass per unit of FFW, neural maturation, or both, contributes to the increase in strength across age in young male athletes.
The present study examined the relative importance of body size and composition as determinants of individual differences in isokinetic leg extensor strength in young adult males performing at slow, moderate, and fast speeds. The subjects were 31 males between the ages of 19 and 29 years, who were not participating in weight training programs. Low to moderate correlations were found between isokinetic strength and body size or body composition measurements. At each speed, similar proportions of the variance in peak torque values were accounted for by lean body weight (23-30%) and thigh volume (20-37%). However, body weight, often suggested as the best reference standard for equalizing strength scores, also accounted for only 13-24% of the variance in peak torque values at each of the speeds tested. The moderate correlations reported in this study do not support the use of body size and composition measurements as a means of adjusting strength values.
The primary purpose of this study was to test the validity of predictive models relating isokinetic knee torque production to anthropometric and demographic variables. Subjects were 23 healthy female and 15 healthy male volunteers between the ages of 10 and 77 years. We measured subjects' peak knee flexion and extension torque production at two angular velocities. For each torque dependent variable, we calculated a Pearson product-moment correlation coefficient between the measured torque values and the values obtained with prediction equations. The difference between the squared value of the correlation coefficients and the regression multiple R2 values obtained for an original group of 134 subjects ranged between .05 and .10 for the torque dependent variables. The results indicate the validity of the regression models at the level specified by the multiple regression R2 values. Clinicians can use the prediction equations presented in this article to establish rehabilitation goals for patients and can estimate the error involved in applying each prediction equation.
The purpose of this study was to develop predictive models relating isokinetic knee testing performance to anthropometric and demographic variables. The subjects were 134 healthy volunteers (70 female, 64 male) between the ages of 10 and 80 years. The investigators measured subjects' peak knee flexion and extension torque production at two angular velocities. Stepwise regression analyses were used to examine the relationship between each torque-dependent variable and the following potential predictor variables: age, sex, side of lower extremity dominance, height, weight, percentage of body fat, and thigh girth. The investigators generated two sets of models designed to predict preinjury knee strength. Clinicians can use one set of models by assessing predictor variables before or immediately following injury. The second set of models involves the assessment of predictor variables postinjury, excluding an assessment of percentage of body fat and thigh girth. The results indicated that peak knee torque production can be predicted with statistically significant accuracy (multiple R = .78-.87). The predictive models generated in this study can be used to establish muscle strength goals for patient rehabilitative programs.
Studies on 500 normal boys and girls indicate that normative values of quantitative muscle strength for children are related to age, height and weight of the subjects. While these variables account only for approximately 50% to 70% of the variance in the observed scores, no other measurable factors could be identified by statistical analysis. Although there are considerable variations in the observed values of muscle strength among homogeneous groups of children characterized by the above 3 variables, the scores show a normal distribution. Two thirds of all measurements fall within a relatively narrower range which was designated arbitrarily the average range of strength. Based on a study population of adequate size, it seems possible to present valid standards and to compute expected strength increments for the various groups of muscles and for boys and girls of different ages.
The muscle strength of selected muscles in 36 normal boys and 34 normal girls was determined by means of the Cybex exerciser dynamometer. Standardized positions were used to permit comparison with accepted manual muscle testing. Strength was expressed in foot/pound torque. Subjects' height, weight, sitting height, biacromial and bicristal diameters as well as limb dominance were obtained according to established procedures. Height and weight percentiles in relation to each subject's age were established. Statistical analysis by means of multiple regression revealed highly significant multiple coefficients for strength with age and height, strength with age and weight, and strength with height and weight. While it can be stated that the reliability of norms can be increased by utilizing many of the parameters examined, in the interest of clinical application a simplified procedure seems to be required. Multifactorial analysis supports the hypothesis that strength can be related most closely with age and height. Standard error of this combination of factors seems to be smallest. Test retest reliability of the procedure, by means of chi2 analysis, was at a 0.01 level of significance.
The use of constant velocity dynamometers in functional testing and in exercise and therapy programs has been increasing in the past few years. For movements in the horizontal plane there are no gravitational errors. However, in vertical movements the limbs are not only working against the dynamometer but also are either aided or opposed by gravity. Far too often these gravitational forces have not been taken into account, and the error involved can be quite large.1.
A study on four subjects using knee extension (against gravity) and flexion (with gravity) showed the error in mechanical work to vary from 26–43% in extension and from 55–510% in flexion.
2.
A relatively simple solution is offered to overcome the problem by compensating for the gravitational errors over the full range of movement. The time course of the error is such as to cause erroneous magnitudes of recorded moments which are a maximum at low level contractions and minimum at high level contractions.
3.
The effect of gravitational and other acceleration errors are such as to cause false early peaks in the muscle moment curves resulting in erroneous conclusions about muscle function.
The development of active isokinetic dynamometers has allowed the assessment of muscular moment under eccentric activations that have different characteristics to concentric actions. It is well documented that at a given angular velocity the eccentric moment is greater than the corresponding concentric moment. The moment-velocity relationship under eccentric conditions has been investigated, with conflicting results. Particularly, eccentric moment was reported to remain similar to, or to increase or decrease with, increasing angular velocity. As with concentric actions, the reliability of isokinetic eccentric measurements is influenced by a number of factors such as gravity, preload force and testing position. Isokinetic dynamometers provide some unique characteristics for rehabilitation applications. Examination of the clinical application of eccentric exercise is limited. Consequently, the use of this exercise modality in prevention and assessment of musculoskeletal injuries should be investigated further.
The purpose of this study was to compare different methods of gravity correction in isokinetic dynamometry. The gravitational moment of the left leg-foot segment of 25 males was measured on a Biodex dynamometer at 30 degrees of knee flexion statically, and as the segment was passively falling from 0 degree to 90 degrees with a constant velocity of 0.035 rad.s-1. The tests were performed in a supine and a seated position. The gravitational moments were also estimated from anthropometric data and directly, using a reaction board method that was considered as the criterion measurement. Furthermore, the isokinetic maximum moment output of the knee flexors and extensors was measured and corrected for gravity using the above methods at angular velocities of 0.52 rad.s-1 and 2.62 rad.s-1 during eccentric, and at 0.52 rad.s-1, 2.62 rad.s-1, and 4.71 rad.s-1 during concentric activations. One-way repeated-measures analysis of variance tests revealed significant differences (P < 0.05) between the gravitational moments obtained on the isokinetic dynamometer and those estimated from anthropometric data or by the reaction board method. The maximum extensor and flexor moments were significantly different, corrected using the gravity correction methods on the dynamometer relative to the anthropometric model or the reaction board (P < 0.05). These results suggest that the determination of gravitational moments based on anthropometric data is more accurate than current gravity correction methods. This new proposed method should be implemented in isokinetic dynamometry applications.
The purpose of this study was to compare electromyographic (EMG) activity and joint moment of agonists and antagonists between isokinetic eccentric and concentric knee muscle actions.
Twelve females (20.5 +/- 2.9 yr) performed maximum knee extension and flexion effort on a Biodex dynamometer isometrically and at concentric and eccentric angular velocities ranging from 30 degrees.s-1 to 150 degrees.s-1. EMG activity of vastus lateralis, rectus femoris, vastus medialis, and hamstrings was also recorded. The moment and agonist EMG values were normalized as a percentage of the maximum isometric values. The antagonist EMG was normalized as a percentage of the IEMG activity of the same muscle group when acting as agonist at the same angular velocity and angular position and taking into consideration the effects of muscle action.
Three-way ANOVA designs indicated significantly greater normalized eccentric moments compared with concentric moments (P < 0.05), whereas the eccentric normalized integrated EMG (IEMG) of agonists and antagonists was significantly lower compared with the respective concentric IEMG values (P < 0.05). These differences were more evident at fast angular velocities.
The present results demonstrate that neural activation and the resulting muscular action are different between isokinetic eccentric and concentric tests and depend also on the angular velocity of the movement. The antagonist IEMG activity is different depending on the muscle examined. The IEMG activity of the antagonists in this study indicate that the antagonist activity is an important factor that affects the resultant joint moment during isolated isokinetic maximum voluntary joint movements.
Champaign Ill: Human Kinetic Publishers
- D Perrin
- Exercise
- Assessment
Perrin D. lsokinetic Exercise and Assessment. Champaign
Ill: Human Kinetic Publishers; 1993.
lsokinetic strength during childhood and adolescence
- V Baltzopoulos
- E Kellis
Baltzopoulos V, Kellis E. lsokinetic strength during childhood and adolescence. In: Van Praagh E, ed. Pediatric
Anaerobic Performance. Champaign, Ill: Human Kinetics;
1998:225-240.
lsokinetic eccentric exercise
- E Kellis
- V Baltzopoulos
Kellis E, Baltzopoulos V. lsokinetic eccentric exercise.
Sports Med. 1995;19:202-222.
Growth and maturation: normal variation and effect of training
- R M Malina
Malina RM. Growth and maturation: normal variation and
effect of training. In: Gisolfi C, Lamb D, eds. Perspectives
in Exercise Science and Sports Medicine; Youth, Exercise
and Sport. Vol 2. Indiana, Pa: Benchmark Press; 1989:
223-272.
Age and sex associated variation in strength during childhood: anthropometric, morphologic, neurologic, biomechanical, endocrinological, genetic and physical activity correlates
- C Blimkie
Blimkie C. Age and sex associated variation in strength
during childhood: anthropometric, morphologic, neurologic, biomechanical, endocrinological, genetic and
physical activity correlates. In: Gisolfi C, Lamb D, eds.
Perspectives in Exercise Science and Sports Medicine;
- Youth
Youth, Exercise and Sport Vol 2. Indiana, Pa: Benchmark
Press; 1989:99-163.
lsokinetic Exercise and Assessment
- D Perrin
Perrin D. lsokinetic Exercise and Assessment. Champaign
Ill: Human Kinetic Publishers; 1993.
Growth and Adolescence
- J Tanner
Tanner J. Growth and Adolescence. 2nd ed. Oxford:
Blackwell; 1962.