Profil isocinétique des muscles fléchisseurs et extenseurs du genou dans une population d'athlètes sauteurs

Introduction. – This study explored concentric and eccentric profile of knee musculature in a jumpers population. Relationships between isokinetic assessment and field tests performances have also been explored.Materials. – Jumpers population presented higher knee flexors performances in concentric and eccentric mode and superior knee extensors strength in eccentric. Significant correlations between isokinetics and field tests results were exclusively observed with athletes quadriceps performances. A very high correlation (r = 0.93) was found between the second bound relative performance of the ten multijumps test and eccentric quadriceps relative peak torque.Conclusion. – Jumpers training may favour a specific muscular development. The knee extensors eccentric strength may be a major factor in the athletic performance.     

强化循环训练对新兵膝屈伸肌功能影响的等速测试研究

目的　研究强化循环训练对新兵膝屈伸肌功能的影响。方法　 16 0名新兵进行 8周强化循环训练 ,训练前后采用Cybex 6 0 0 0型等速运动测试仪对膝屈伸肌肌力、肌爆发力及肌耐力进行等速测试并加以比较。结果　新兵训练后双膝屈伸肌的峰力矩、力矩加速能和耐力比在不同测试速度 (6 0°/s,180°/s)时有不同程度的提高 ,训练前后相比差异有统计学意义 (P <0 0 5 )。结论　 8周的强化循环训练能达到全面发展新兵膝屈伸肌肌力、肌爆发力和肌耐力的目的。     

Concentric and eccentric shoulder and elbow muscle strength in female volleyball players and non-active females

Alfredson H, Pietilä T, Lorentzon R. Concentric and eccentric shoulder and elbow muscle strength in female volleyball players and non-active females. Maximal isokinetic concentric (60°/s and 180°/s) and eccentric (60°/s) muscle strength of the external and internal rotator muscles of the shoulder and the flexor and extensor muscles of the elbow was measured in a position resembling spiking and serving in volleyball, on 11 non-injured female volleyball players (first division) and 11 non-active females. In the dominant arm, the volleyball players had significantly higher concentric peak torque of the internal and external rotators and elbow extensors at both velocities, and significantly higher eccentric peak torque of the shoulder internal and external rotators and elbow flexors and extensors, than the controls. In the volleyball group, the concentric internal rotation peak torque at 60°/s was significantly higher in the dominant than in the non-dominant arm. The external/internal strength ratio was significantly lower at 60°/s, but not at 180°/s, in the dominant arm. Conclusion: The female volleyball players had a higher concentric and eccentric strength in the rotator muscles of the shoulder and in the extensor muscles of the elbow compared to untrained controls in this special test position. There were signs of rotator muscle imbalance at the low test speed, but no signs of weakness of the external rotators, in the dominant arm of the volleyball players.     

Deficits in eccentric versus concentric torque in children with spastic cerebral palsy

PURPOSE: The purposes of this study were to determine whether ambulatory children with spastic cerebral palsy (CP) had abnormal isokinetic eccentric peak torque values at the knee and ankle, and to gain further insights on the influence of spasticity on voluntary force production in this population. METHODS: Twenty-four children with spastic CP (mean = 11.1+/-2.6 yr) and twenty children of comparable age with no neuromotor pathology (mean = 10.3+/-2.6 yr) participated in an isokinetic testing protocol on a Biodex dynamometer that measured eccentric and concentric peak torques of the knee extensors, knee flexors, ankle dorsiflexors, and ankle plantarflexors. Angular velocity of the eccentric trials was 30 degrees x s(-1) and of the concentric trials was 30 degrees x s(-1), 60 degrees x s(-1), and 120 degrees x s(-1). Peak torque values were normalized by body weight and compared across groups by using ANOVA procedures. Eccentric to concentric (E/C) peak torque ratios at 30 degrees x s(-1) were computed for each muscle and compared across groups. The torque values in CP were also expressed as a percent of the mean normalized value of the comparison group and compared across conditions using repeated measures ANOVA (P < 0.05). RESULTS: Children with CP demonstrated decreased eccentric and concentric peak torques for all muscle groups tested. The relative deficit in eccentric torque was less than the concentric torque and the decrement in concentric torque across speeds was greater in CP for all muscle groups except the ankle dorsiflexors. The E/C ratios for the knee extensors and flexors were also greater in CP. CONCLUSIONS: Children with CP have diminished eccentric as well as concentric peak torques at the knee and ankle. The influence of spasticity on voluntary force production can be inferred from the bias toward greater eccentric torque and the greater decrement in concentric torque across speeds in children with spastic CP.     

Knee flexor strength and rate of torque development deficits in women with patellofemoral pain are related to poor objective function

BackgroundDeficits in knee flexor strength and rate of torque development (RTD) might be present in women with patellofemoral pain (PFP). In addition, maximal strength and RTD of the knee flexors and extensors might be related with subjective and objective function in women with PFP. However, both conjectures are still poorly understood.Research questionDo women with PFP have deficits in the maximal strength and RTD of the knee flexors and extensors during isometric, concentric, and eccentric contractions? Is there a relationship between maximal strength and RTD of the knee flexors and extensors with subjective and objective function in women with PFP?MethodsFifty-six women with, and 46 women without, PFP participated. Maximal strength and RTD (to 30% and 60% maximal torque) during isometric, concentric, and eccentric contractions of the knee flexors and extensors were assessed using an isokinetic dynamometer. Objective assessment included single leg hop test (SLHT) and forward step-down test (FSDT). Subjective assessment involved the anterior knee pain scale.ResultsWomen with PFP had small to large deficits in maximal strength and RTD of the knee flexors and extensors during isometric, concentric and eccentric contractions (Effect sizes: -0.43 to -1.10; p ≤ 0.016). Small to moderate correlations of maximal concentric and eccentric knee flexor strength and RTD with SLHT and FSDT (r = 0.28 to 0.41; p ≤ 0.037) were identified. Subjective or objective function were not correlated with maximal isometric knee flexor strength and RTD, or any knee extensor measures (p > 0.05).SignificanceMaximal strength and RTD deficits of the knee flexors and extensors were identified in this female PFP cohort, but they were unrelated to subjective function. The relationship of concentric and eccentric knee flexor strength and RTD deficits with poor objective function should be considered in future exercise trials for women with PFP.     

Reproducibility of isokinetic knee eccentric and concentric strength indices in asymptomatic young adults

ObjectiveTo assess the reproducibility of isokinetic eccentric and concentric knee extension and flexion strength indices obtained at two different angular velocities.DesignCohort study.SettingUniversity human performance laboratory.Participants45 healthy physically active young adults (25 males).Main outcome measuresA non reciprocal protocol of concentric and eccentric contractions of the knee extensors and flexors was performed at 30 and 120°/s. Strength indices evaluated included peak moment; dynamic control ratios; and the difference between eccentric and concentric ratio at the two angular velocities.ResultsNo evidence for inter-test bias in any of the strength indices was noted. Measurement precision for peak moment, as quantified using ratio limits of agreement, suggest that scores may be expected to vary up to 15% for the knee extensors in both eccentric and concentric contraction modes. An error of up to 19% was calculated for the peak moment scores of the knee flexors. Intraclass correlation coefficients revealed fairly robust preservation of participants’ rank order for the majority of strength indices (>0.85).ConclusionIsokinetic-related indices of knee muscles performance enable an acceptable level of detection of expected changes in muscular strength parameters as a result of planned interventions.     

Strength training effects in prepubescent boys

Possible changes in muscle size and function due to resistance training were examined in prepubertal boys. Thirteen boys (9-11 yr) volunteered for each of the training and control groups. Progressive resistance training was performed three times weekly for 20 wk. Measurements consisted of the following: 1 repetition maximum (RM) bench press and leg press; maximal voluntary isometric and isokinetic elbow flexion and knee extension strength; evoked isometric contractile properties of the right elbow flexors and knee extensors; muscle cross-sectional area (CSA) by computerized tomography at the mid-right upper arm and thigh; and motor unit activation (MUA) by the interpolated twitch procedure. Training significantly increased 1 RM bench press (35%) and leg press (22%), isometric elbow flexion (37%) and knee extension strength (25% and 13% at 90 degrees and 120 degrees, respectively), isokinetic elbow flexion (26%) and knee extension (21%) strength, and evoked twitch torque of the elbow flexors (30%) and knee extensors (30%). There were no significant effects of training on the time-related contractile properties (time to peak torque, half-relaxation time), CSA, or %MUA of the elbow flexors or knee extensors. There was, however, a trend toward increased MUA for the elbow flexors and knee extensors in the trained group. Strength gains were independent of changes in muscle CSA, and the increases in twitch torque suggest possible adaptations in muscle excitation-contraction coupling. Improved motor skill coordination (especially during the early phase of training), a tendency toward increased MUA, and other undetermined neurological adaptations, including better coordination of the involved muscle groups, are likely the major determinants of the strength gains in this study.     

Influence of acute eccentric exercise on the H:Q ratio

The purpose of the present study was to examine the effects of an acute bout of eccentric exercise on maximal isokinetic concentric peak torque (PT) of the leg flexors and extensors and the hamstrings-to-quadriceps (H:Q) strength ratio. Sixteen male (mean±SD: age=20.9±2 years; stature=177.0±4.4 cm; mass=76.8±10.0 kg) volunteers performed maximal, concentric isokinetic leg extension and flexion muscle actions at 60°·sec?-?1 before and after (24-72 h) a bout of eccentric exercise. The eccentric exercise protocol consisted of 4 sets of 10 repetitions for the leg press, leg extension, and leg curl exercises at 120% of the concentric one repetition maximum (1-RM). The results indicated that the acute eccentric exercise protocol resulted in a significant (P<0.05) decrease in isokinetic leg flexion (13-19%) and leg extension (11-16%) PT 24-72 h post-exercise. However, the H:Q ratios were unaltered by the eccentric exercise protocol. These findings suggest that an acute bout of eccentric exercise utilizing both multi - and single - joint dynamic constant external resistance (DCER) exercises results in similar decreases in maximal isokinetic strength of the leg flexors and extensors, but does not alter the H:Q ratio.     

Muscular strength changes in hospitalized anorexic patients after an eight week resistance training program

We investigated whether an eight week, light resistance program could increase the muscular strength of the knee and elbow extensors and flexors in a group of hospitalized anorexic patients compared to anorexic controls (AC) who did not participate in the training program, but received the same caloric intake, and non-anorexic exercisers (NAE) who undertook the resistance training program. After the resistance training program, the seven anorexic exercisers (AE) significantly increased the peak torque (PT) of their knee extensors (p < 0.001), flexors (p < 0.0001) and elbow flexors (p < 0.01). In comparison, the seven anorexic non-exercisers (anorexic controls, AC) and seven non-anorexic exercisers (NAE), who performed the same program, showed no significant increase in peak torque after the program (p > 0.05). The study has demonstrated that an eight week, light resistance program increases the knee and elbow strength of the hospitalized anorexic patients.     

Isometric and isokinetic knee joint performance in Japanese alpine ski racers.

Isometric and isokinetic (concentric and eccentric, strength of alpine skiers with different performance levels were measured. Nine national (elite, EG) and 10 collegiate (trained, TG) female alpine skiers (16 to 23 years of age) performed maximal voluntary knee extension and flexion. Peak torque was measured at an angular velocity of 30 deg.s-1. The cross-sectional area (CSA) of thigh muscles (quadriceps and hamstring muscles) was determined by an ultrasonic method. No significant differences in anthropometric variables and CSA were observed between EG and TG. EG had significantly greater (p < 0.01 for extensors and p < 0.05 for flexors) eccentric knee extensor and flexor strength than that of TG whereas no significant differences were noted in isometric and concentric strength. Eccentric strength/CSA ratio was also higher for EG than for TG. It was suggested that knee extension and flexion strength during eccentric muscle action might be related to the performance level of alpine skiers.     

Reliability of isokinetic normalized peak torque assessments for knee muscles in post-stroke hemiparesis

The purpose of this study was to establish test–retest reliability of measurement procedures for quantifying isokinetic concentric peak torque (PT) at the knee using normalization methods post-stroke. A second aim was to estimate the change required to show clinically significant improvements in knee muscles strength. The isokinetic normalized PT (NPT) values for the knee extensors and flexors were measured in each participant at two different angular velocities during two sessions 1 day apart. Thirty participants with mild to moderate hemiparesis after stroke who were able to walk were tested. The normalized PT measures for the knee muscles of the affected lower extremity were highly reliable (intraclass correlation coefficients ranged from 0.85 to 0.98; p < 0.05). Size of relative changes (the percent smallest real difference, SRD%) for extensors NPT (ranged from 22.35% to 25.68%) were lower than flexors NPT (ranged from 74.01% to 76.31%), indicating that the affected isokinetic knee flexors had more random variation than the knee extensors. This study supports the use of isokinetic dynamometers for the assessment of knee muscle strength in participants with chronic mild to moderate post-stroke hemiparesis and to measure clinical improvements. Established measurement error and smallest real differences in normalized PT will aid interpretation of real changes in muscle strength in this clinical population.     

膝关节屈肌和伸肌等速向心、等速离心及等长测试的研究

本文通过运用Ｃｙｂｅｘ－６０００型等速测力系统对２５名健康男青年膝屈肌和伸肌进行等速向心、等速离心及等长测试，来比较膝肌肉向心收缩、离心收缩和等长收缩的功能，并探讨其相互间的关系。结果表明：等速测试时，膝屈肌和伸肌离心收缩的肌力明显大于向心收缩。在膝屈曲６０°时，离心收缩和等长收缩的肌力同样明显大于向心收缩，但离心收缩与等长收缩相比无显著性差异。随运动速度增加，屈肌和伸肌向心收缩的肌力明显下降，而离心收缩的肌力无明显变化。     

Characteristics of isometric and dynamic strength loss following eccentric exercise-induced muscle damage

Angle-specific isometric strength and angular velocity-specific concentric strength of the knee extensors were studied in eight subjects (5 males and 3 females) following a bout of muscular damaging exercise. One hundred maximal voluntary eccentric contractions of the knee extensors were performed in the prone position through a range of motion from 40 degrees to 140 degrees (0 degrees = full extension) at 1.57 rads(-1). Isometric peak torque was measured whilst seated at 10 degrees and 80 degrees knee flexion, corresponding to short and optimal muscle length, respectively. Isokinetic concentric peak torque was measured at 0.52 and 3.14 rad x s(-1). Plasma creatine kinase (CK) activity was also measured from a fingertip blood sample. These measures were taken before, immediately after and on days 1, 2, 4, and 7 following the eccentric exercise. The eccentric exercise protocol resuited in a greater relative loss of strength (P< 0.05) at short muscle length (76.3 +/- 2.5% of pre-exercise values) compared to optimal length (82.1 +/- 2.7%). There were no differences in the relative strength loss between isometric strength at optimal length and isokinetic concentric strength at 0.52 and 3.14 rad x s(-1). CK activity was significantly elevated above baseline at days 4 (P < 0.01) and 7 (P < 0.01). The greater relative strength loss at short muscle length appeared to persist throughout the seven-day testing period and provides indirect evidence of a shift in the angle-torque relationship towards longer muscle lengths. The results lend partial support to the popping sarcomere hypothesis of muscle damage, but could also be explained by an impairment of activation at short muscle lengths.     

Isokinetic strength training program for muscular imbalances in professional soccer players

The aim of the study was to investigate the effect of a muscular training program on soccer players’ performance of which initially appeared imbalances or deficits. The study was conducte on 68 professional soccer players (age, 24.1±5.7 years; weight, 76.8±5.7 kg; height, 1.82±7 cm) participating in the championship of the first Greek national division over 2 years. During the preparation period, all the players performed an isokinetic test of knee flexors and extensors (60° s⁻¹ and 180° s⁻¹). These initial measurements detected muscular imbalances or deficits in 27 players (40%). The 27 players followed a specific isokinetic training program for 2 months, 3 times per week. After completion of the isokinetic training program, the 68 players repeated the isokinetic test. The analysis revealed significant differences between the pre-and post-training measures at both angular velocities in peak torque values, in differences from one limb to the other, and in peak torque ratios for flexors and extensors. Consequently, the application of this specific isokinetic training program can restore imbalances in knee muscle strength efficiently.     

Acute effects of static and dynamic stretching on leg flexor and extensor isokinetic strength in elite women athletes

The aim of this study was to explore the effects of static and dynamic stretching of the leg flexors and extensors on concentric and eccentric peak torque (PT) and electromyography (EMG) amplitude of the leg extensors and flexors in women athletes. Ten elite women athletes completed the following intervention protocol in a randomized order on separate days: (a) non‐stretching (control), (b) static stretching, and (c) dynamic stretching. Stretched muscles were the quadriceps and hamstring muscles. Before and after the stretching or control intervention, concentric and eccentric isokinetic PT and EMG activity of the leg extensors and flexors were measured at 60 and 180°/s. Concentric and eccentric quadriceps and hamstring muscle strength at both test speeds displayed a significant decrease following static stretching (P<0.01–0.001). In contrast, a significant increase was observed after dynamic stretching for these strength parameters (P<0.05–0.001). Parallel to this, normalized EMG amplitude parameters exhibited significant decreases following static (P<0.05–0.001) and significant increases following dynamic stretching (P<0.05–0.001) during quadriceps and hamstring muscle actions at both concentric and eccentric testing modes. Our findings suggest that dynamic stretching, as opposed to static or no stretching, may be an effective technique for enhancing muscle performance during the pre‐competition warm‐up routine in elite women athletes.     

Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study

ABSTRACT

Background: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.

Methods: Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer.

Results: For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and the average power of U15 group were significantly higher than U13 group. Extensor muscle average power of the PRO group was higher than U17. Dominant knee flexor average power of U15 was significantly higher than the U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of the PRO group were higher than the U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than the U15 group for the dominant limb.

Conclusions: The greatest improvement in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury.     

Relation entre la force isocinétique,le saut et le sprint chez le footballeur de haut niveau

Purpose – The aim of this study is to appreciate the relation between sprint, jump and knee isokinetic torque in high-level soccer players.Methods – Twenty soccer players (first french national division) were evaluated by sprint and jump tests. Extensors and flexors isokinetic torque was measured by a Cybex Norm dynamometer. Relations between sprints, jumps and isokinetic peak torque were appreciated after correlation analysis.Results – Jumps are correlated with the extensors concentric peak torque at the speed of 180° s⁻¹ when values were corrected by weight (Squat Jump: r = 0.507; Countermovement Jump: r = 0.649; Vertical Jump: r = 0.496). Sprints are correlated with the extensors concentric peak torque at the speed of 180° s⁻¹ when values were corrected by weight (10 and 20 m fixed departure sprint: r = −0.427 and −0.548; 10 and 20 m thrown departure sprint: r = −0.406 and −0.480). Furthermore, sprints with fixed departure are conversely correlated with the flexors eccentric peak torque at the speed of 60° s⁻¹ (r = 0.546 and 0.478) doubtless because a mechanism of knees protection.Conclusions – According to these causal relations, knee extensors and flexors strengthening is recommended for high-level soccer players with the aim of improving sprints and jumps.     

Gains in flexibility related to measures of muscular performance: impact of flexibility on muscular performance.

OBJECTIVE: Studies that investigated possible correlations between flexibility and muscular performance are scarce in the literature. Therefore, the purpose of this study was to investigate the impact of a program of static stretching on the flexibility of the hamstrings and on muscular performance of the knee flexors and extensors. DESIGN: Pre-post experimental design. SETTING: University laboratory. PARTICIPANTS: Thirty subjects aged 22.8 +/- 4.9 years with bilaterally shortened hamstrings. INTERVENTION: Using a protocol that has been previously described, the intervention consisted of 30 sessions of static stretching, performed bilaterally five times a week for 6 weeks. MAIN OUTCOME MEASUREMENTS: Measures of knee range of motion and isokinetic muscular performance (peak torque, angle of peak torque, and work) of knee flexors and extensors at speeds of 60 and 300 degrees/s. RESULTS: After intervention, significant gains in measures of flexibility (P < 0.0001) were observed, with an average gain of the knee-extension angle of 12.6 degrees, ranging from -1.2 to 30.7 degrees. In addition, we found significant increases in the following parameters of muscular performance: angle of peak torque of hamstrings at 60 and 300 degrees/s (P < 0.0001 and 0.018) and for work at 60 and 300 degrees/s for knee flexors (P = 0.012 and 0.005) and for knee extensors (P < 0.0001). CONCLUSIONS: The intervention resulted in gains in measures of flexibility, and these gains had a positive impact on some parameters of muscular performance.     

Hamstring muscle strain recurrence and strength performance disorders

We determined the frequency of strength disorders in 26 athletes with a history of hamstring muscle injury and recurrent strains and discomfort. We also assessed the effectiveness of rehabilitation to correct muscle performance. After concentric and eccentric isokinetic assessment, 18 athletes were found to have strength deficits, as determined by statistically selected cutoffs of peak torque, bilateral differences, and the flexors/quadriceps ratio. The discriminating character of the eccentric trial was demonstrated, combining a preferential eccentric peak torque deficit and a significant reduction of the mixed eccentric flexors/concentric quadriceps ratio. The athletes with muscle imbalances followed a rehabilitation program individually adapted from their strength profile. Treatment length was from 10 to 30 sessions and resulted in isokinetic parameter normalization in 17 of 18 subjects. Isokinetically corrected subjects were observed for 12 months after return to athletics. None sustained a clinically diagnosed hamstring muscle reinjury. Subjective intensity of pain and discomfort were significantly reduced, and they all returned to their prior level of competition. These results demonstrate that persistent muscle strength abnormalities may give rise to recurrent hamstring injuries and discomfort. An individualized rehabilitation program emphasizing eccentric training based on specific deficits contributes to a decrease in symptoms on return to sports.     

中国女子篮球运动员膝关节等速肌力测试分析

目的:了解中国国家女子篮球队运动员膝关节等速肌力特征。方法:选用IsoMed 2000等速测试系统,采用60°/s、180°/s、240°/s三种角速度,测试18名中国女篮国家队运动员膝关节等速肌力。根据场上位置将运动员分为三组:后卫组7人(1、2号位),前锋组6人(3、4号位),中锋组5人(5号位),比较分析三组运动员的测试结果。结果:(1)女篮运动员双侧膝关节慢速测试时(60°/s)屈伸肌峰力矩(PT)显著高于快速测试(180°/s,240°/s),膝关节屈伸肌峰力矩比值(H/Q)随测试速度增加递增,左右膝H/Q无显著性差异。(2)慢速测试时(60°/s),左右膝关节峰力矩、峰力矩/体重比值、平均功率、H/Q无显著差异。(3)快速测试(240°/s)时,左膝屈肌PT、峰力矩/体重比值(PT/BW)显著高于右膝。180°/s测试时,左膝屈肌平均功率显著高于右膝。(4)60°/s测试时,后卫、前锋、中锋运动员PT、PT/BW组间比较无显著性差别。180°/s测试时,后卫运动员左膝屈肌PT与前锋、中锋运动员比较有显著性差异(P=0.02),各组间伸肌PT未见显著差异。240°/s测试时,后卫运动员右膝屈、伸肌PT/BW和中锋运动员比较均存在显著差异;后卫、前锋、中锋三组运动员平均功率、H/Q、总功与峰值功率组间比较均无显著性差别。结论:(1)女篮运动员快速测试(240°/s)时左膝屈肌力量强于右膝,反映快速运动时左右膝关节肌力不平衡。(2)不同场上位置女篮运动员膝关节等速肌力快速测试结果有差异性,提示力量训练应根据场上位置进行特异性训练。(3)女篮运动员需加强屈肌快速力量训练,以提高H/Q,预防膝关节损伤。