Effects of age on the reciprocal peak torque ratios during knee muscle contractions in elite soccer players

To investigate the effects of age on the reciprocal peak torque ratios during knee muscle contractions, 25 elite male soccer players, aged 22.3 +/- 3.8 yr (18-28), volunteered for the present study. The players were grouped as adult (> 21 years, n = 13) and young players (< or = 21 years, n = 12). Maximal concentric (CON) and eccentric (ECC) isokinetic thigh muscle strength was measured at angular velocities of 30 degrees, 180 degrees, 240 degrees and 300 degrees/s. ECC and CON peak torques of knee flexors (hamstring, HAM) and CON peak torques of knee extensors (quadriceps, QUA) in the dominant knee were greater (P < 0.05) in adult players than in young players at 180, 240 and 300 degrees/s. ECC HAM/CON QUA peak torque ratio at 300 degrees/s was greater (P < 0.05) for adult players compared to young players in the dominant knee but not in the nondominant knee. Furthermore, conventional HAM/QUA peak torque ratios of the dominant knee at all angular velocities for ECC contraction were higher (P < 0.05) in adult players than in young players. In conclusion, the findings of the present study indicate that the reciprocal torque ratio is influenced by age in the dominant knee of elite soccer players. Because there was no effect of age for the nondominant leg, the findings of the present study are more likely to be the result of the training background of the players than their age.     

Association between polymorphisms of vitamin D receptor gene ApaI, BsmI and TaqI and muscular strength in young Chinese women

The association between the polymorphisms of vitamin D receptor gene ApaI, BsmI and TaqI and isokinetic muscular strength was examined in 109 healthy, young Chinese women. Methods: Genomic DNA was extracted from mouthwash samples and vitamin D receptor genotypes were determined with the established methods. The peak torque of the dominant limb in concentric and eccentric knee extensors and flexors and elbow extensors and flexors was measured using Cybex-Norm-770 isokinetic dynamometer at slow and fast velocities. The distribution frequency of vitamin D receptor gene alleles was analyzed by chi-square test. The difference in muscular strength between VDR genotype groups was analyzed using one-way ANOVA. The ApaI, BsmI and TaqI alleles and genotype frequencies appeared to be in a Hardy-Weinberg equilibrium. Subjects with the vitamin D receptor ApaI null (A allele) mutation (AA) exhibited significantly lower knee and elbow concentric or eccentric peak torque than those with aa homozygous or Aa heterozygous. The BB & Bb group showed significantly higher peak torque in concentric knee flexors than bb group. No association was found between vitamin D receptor gene TaqI and muscular strength. The data indicated that vitamin D receptor gene ApaI and BsmI polymorphisms rather than TaqI polymorphism might be associated with muscular strength.     

The influence of age on isokinetic torque of the upper and lower leg musculature in sedentary men.

While strength patterns in aging for the knee joint have been well investigated in the concentric mode, few data are available about the behaviour in the eccentric mode and for either modus in the ankle. The purpose of this study was to compile reference data for the lower extremities in untrained men between 20 and 60 years of age to determine the influence of age, especially in the eccentric work mode. Sixty-four male subjects between 20 and 60 years were divided into four age groups. Using a LIDO ACTIVE dynamometer, maximum torque was tested for the knee between 90 degrees to 0 degrees and for the ankle between 30 degrees to -10 degrees at velocities 60, 180, 240, 300 degrees/s concentric, 60 and 120 degrees/s eccentric and isometric with angles 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees for the knee and 30 degrees, 20 degrees, 10 degrees, 0 degrees , -10 degrees for the ankle. Individual parameters for age-dependence were checked using linear correlation calculation with p < 0.01 set as significant. The peak torque (PT) of the knee extensors and flexors showed a typical course with the highest values in the eccentric and isometric mode and a decrease in the concentric mode with increasing angular velocity. In the concentric mode there was a significant negative correlation between PT and age at all angular velocities, but none for isometric and eccentric mode. The greatest maximum torque in the ankle was attained in the eccentric mode at 60 degrees/s. The difference to the knee was smallest in this mode compared to isometric and concentric. The plantar flexion showed age-dependence at all concentric velocities, less in eccentric and none in isometric mode. There was no correlation in dorsiflexion. The influence of loss of muscle fiber and degeneration in the course of aging has thus less influence in eccentric measurements than in the concentric mode. On the contrary, it must be assumed that the high eccentric tensions which are possible due to the quasi-elastic structures in the muscle, are maintained by the increase in stiffness of the connective tissue.     

优秀击剑运动员下肢三关节等速肌力测试分析

目的:研究我国优秀击剑运动员下肢髋、膝、踝三关节肌群等速肌力表现,找出薄弱肌群。方法:国家击剑队备战2008年奥运会重点队员26名,男女各13名,年龄23.1±2.36岁。在60°/s、240°/s速度下测定运动员双侧下肢髋、膝、踝屈伸肌群等速向心峰力矩。结果发现:(1)髋关节:在240°/s下双侧伸肌峰力矩均明显低于60°/s(P<0.05),60°/s和240°/s下双侧髋关节屈肌峰力矩无显著差异(P>0.05);男运动员两个速度下前腿伸肌峰力矩均显著高于后腿(P<0.05),女运动员无显著差异(P>0.05);两个速度下,运动员双腿屈伸肌峰力矩比值低于正常。(2)膝关节:60°/s时男运动员双腿屈伸肌峰力矩有显著差异(P<0.05),240°/s时双侧伸肌峰力矩有显著差异(P<0.05),女运动员两个速度下均无显著差异(P>0.05);60°/s时,女运动员前后腿屈伸肌峰力矩比值分别为0.56和0.54,男运动员分别为0.63和0.67;240/°s时男女前后腿屈伸肌峰力矩比值均在正常范围。(3)踝关节:60°/s时男运动员前腿踝关节屈伸肌峰力矩显著大于后腿(P<0.05),240°/s时无显著差异(P>0.05);两个速度下,女运动员踝关节屈伸肌峰力矩均无显著性差异(P>0.05);运动员踝关节屈伸峰力矩比值在两个速度下均低于正常。结论:优秀男子击剑运动员下肢关节等速肌力双侧不对称,女运动员不对称表现不明显;击剑运动员下肢薄弱肌群为后腿髋关节伸肌群、股后肌群、前腿股后肌群及踝关节背伸肌群。     

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.     

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。     

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.     

Muscle strength and size balances between reciprocal muscle groups in the thigh and lower leg for young men

The present study investigated whether the muscle size balance affects the muscle strength balance between reciprocal muscle groups in the thigh and lower leg. 18 young men volunteered as subjects. The joint torques developed during isometric maximal voluntary knee extension and flexion, plantar flexion and dorsiflexion were measured using a dynamometer. The muscle volumes of knee extensors and flexors, plantar flexors and dorsiflexors were determined by magnetic resonance imaging. For each of the muscle groups, the joint torque was significantly correlated with the muscle volume (r=0.644-0.847) and the y-intercept of the regression line between them was not significantly different from zero. Based on these observations, the dependencies of muscle strength balance on muscle size balance between the knee extensors and flexors and between the plantar flexors and dorsiflexors were investigated using the joint torque and muscle volume. The correlation between muscle volume ratio and joint torque ratio was significant between the plantar flexors and dorsiflexors (r=0.622) but not between the knee extensors and flexors (r=0.128). Thus, it is suggested that the strength balance is strongly affected by the size balance between the reciprocal muscle groups in the lower leg but not in the thigh.     

Effects of aquatic resistance training on neuromuscular performance in healthy women

PURPOSE: The purpose of this study was to investigate the effects of a progressive 10-wk aquatic resistance training on neuromuscular performance and muscle mass of the knee extensors and flexors in healthy women. METHODS: Twenty-four healthy women (34.2 +/- 3.9 yr) were randomly assigned into aquatic exercise (N = 12) and control group (N = 12). Maximum knee extension and flexion torques were measured isometrically and at constant angular velocities of 60 degrees x s(-1) and 180 degrees x s(-1) (isokinetic) with simultaneous electromyography (EMG) recordings of the quadriceps and hamstrings. The lean muscle mass (LCSA) of the quadriceps and hamstring muscles was determined by computed tomography scanning. RESULTS: Significant interaction of group by time was observed in each of the measured parameters. The change in extension and flexion isometric/isokinetic torque varied between 8 and 13% and in EMGs between 10 and 27% in the exercise group. The change in the quadriceps LCSA of the exercise group was 4% and in hamstrings 5.5%. CONCLUSIONS: The results of the present study showed that 10 wk of progressive aquatic resistance training resulted in significant improvement in muscle torque of the knee extensors and flexors accompanied with proportional improvement in neural activation and with significant increase in the LCSA of the trained muscles. Aquatic training can be recommended for neuromuscular conditioning in healthy persons.     

Maximal voluntary eccentric,isometric and concentric torque recovery following a concentric isokinetic exercise

To examine neuromuscular fatigue and recovery following an isokinetic fatiguing exercise, nine active females performed a fatiguing exercise comprising of ten sets of ten maximal concentric knee extensions. Before (pre-test), five minutes (post-test), 24 h and 48 h after the fatiguing exercise, maximal voluntary eccentric (-1.05 rad x s(-1); -2.09 rad x s(-1)), isometric (0 rad x s(-1)) and concentric (1.05 rad x s(-1); 2.09 rad x s(-1)) torque were measured. In order to distinguish central from peripheral factors involved in torque decrement, activation level (twitch interpolation technique) and twitch contractile properties were recorded. During the course of the fatiguing exercise, concentric torque was significantly lower during the 3rd set than pre-test (-5.6 +/- 12.3 %) and further decreased to the 10th (-10.3 +/- 9.5 %). Eccentric and isometric torques were significantly lower during post-test than pre-test (-16.8 +/- 8.8 % at -2.09 rad x s(-1), -15.1 +/- 7.4 % at -1.05 rad x s(-1), and -10.4 +/- 5.9 % at 0 rad x s(-1); p < 0.05), while concentric torque was not significantly modified. Voluntary activation, peak twitch torque, twitch maximal rates of force development and relaxation were also significantly declined (p < 0.05) at post-test. Twenty-four hours later, all the measured parameters were close to their pre-fatigue values. The present results reveal that the best way to test concentric-induced alteration of neuromuscular function was to use stressful testing conditions, such as eccentric contractions.     

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.     

Eccentric/concentric training of ankle evertor and dorsiflexors in recreational athletes: Muscle latency and strength

The aim of this study was to investigate the effects of a combined eccentric–concentric exercise program of the ankle evertors and dorsiflexors on the latency time of the peroneus longus and tibialis anterior muscles. Twenty‐four healthy male recreational athletes were admitted to this study and were randomly assigned to either the exercise group (n = 12) or the control group (n = 12). Subjects in the exercise group performed an isokinetic exercise program of the ankle evertors and dorsiflexors in a combined eccentric–concentric mode for 3 days per week for 6 weeks. Before and after the exercise program, muscle reaction times of the peroneus longus and tibialis anterior muscles to sudden supinating maneuvers on a tilting platform, and isokinetic strength of the ankle joint musculature were evaluated. The peroneus longus and tibialis anterior reaction times showed significant (P < 0.01–0.05) reductions following six weeks of intervention in the exercise group. Additionally, eccentric peak torques for the ankle evertor and dorsiflexors represented significant (P < 0.05) increases in the exercise group compared with the control group. The results of this study suggest that it is possible to reduce peroneal and anterior tibial reaction times following a six week eccentric/concentric isokinetic training program in healthy ankles.     

Isoacceleration: a new concept of resistive exercise

This study presents the concept of constant (iso-) accelerative and decelerative exercise and compares concentric and eccentric torque output during isoaccelerative and isodecelerative movements with that during comparable constant velocity (isokinetic) conditions. Twelve men (19-42 yr) performed maximal voluntary concentric and eccentric knee extensions at velocities of 120 and 240 degrees.s-1 (isokinetic) and at accelerations of 180 and 720 degrees.s-2 (both isoaccelerative and isodecelerative) between 10 degrees and 90 degrees knee angles. At 50 degrees, the 180 and 720 degrees.s-2 tests had velocities of 120 and 240 degrees.s-1, respectively, and thus torque comparisons could be made at a corresponding position and velocity. No difference was seen among the isoaccelerative, isodecelerative, or isokinetic angle- and velocity-specific torques for either the concentric or eccentric tests (P greater than 0.05). The results demonstrated that, under conditions of maximal voluntary effort, movement speed as such (within the range studied) was the essential determinant of muscle force--not whether this speed was attained during accelerative, decelerative, or constant velocity movements. As a testing and training modality, the controlled acceleration technique, particularly eccentric deceleration and concentric accleration, appears to offer advantages as compared with existing methods, since it more faithfully reflects the contraction conditions during natural strength-requiring movements.     

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.     

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。     

Effects of long term Tai Chi practice and jogging exercise on muscle strength and endurance in older people

Objectives

To investigate the influence of regular Tai Chi (TC) practice and jogging on muscle strength and endurance in the lower extremities of older people.

Methods

Twenty one long term older TC practitioners were compared with 18 regular older joggers and 22 sedentary counterparts. Maximum concentric strength of knee flexors and extensors was tested at angular velocities of 30°/s and 120°/s. Ankle dorsiflexors and plantar flexors were tested at 30°/s and the dynamic endurance of the knee flexors and extensors was assessed at a speed of 180°/s.

Results

The differences in the muscle strength of the knee joint amongst the three experimental groups were significant at the higher velocity. The strengths of knee extensors and flexors in the control group were significantly lower than those in the jogging group and marginally lower than those in the TC group. For the ankle joint, the subjects in both the TC and jogging groups generated more torque in their ankle dorsiflexors. In addition, the muscle endurance of knee extensors was more pronounced in TC practitioners than in controls.

Conclusion

Regular older TC practitioners and joggers showed better scores than the sedentary controls on most muscle strength and endurance measures. However, the magnitude of the exercise effects on muscles might depend on the characteristics of different types of exercise.     

The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.     

Validity of lower extremity strength and power utilizing a new closed chain dynamometer

PURPOSE: The purpose of this study was to compare selected variables measured on a traditional isokinetic dynamometer (Cybex II) with a new lower extremity, closed chain dynamometer (Omnikinetic, OmK). METHODS: Twelve subjects (6 male, 6 female, age = 28+/-5 yr, mean +/- SD) performed Cybex II knee flexion and extension at 1.05, 3.14, and 5.23 rad x s(-1). A maximal effort of 10 repetitions of lower extremity concentric extension and eccentric flexion at 36% of subject's 1-RM was performed on the OmK. Crank power and joint (ankle, knee, and hip) kinetics were recorded as a mean of 10 repetitions. RESULTS: t-Tests revealed right versus left leg differences (P < 0.05) for Cybex II peak torque flexion at 5.23 rad x s(-1), and OmK knee and hip peak power and hip root mean square power (RMS) power. Cybex peak knee torques were related (Pearson r values 0.78-0.92, P < 0.01) to OmK peak knee torques. Cybex average power was related to OmK knee power (Pearson r values 0.71-0.96, P < 0.01) and OmK crank power (r = 0.62-0.94, P < .01). Correlations tended to be stronger comparing the OmK with the fastest (5.23 rad x s(-1)) Cybex II speed. CONCLUSIONS: These results suggest that the OmK knee and crank kinetic data are comparable to Cybex It isokinetic dynamometry. The ability to evaluate lower extremity joint exercise at a subject's maximal movement speed, in addition to the use of a closed-chain, multi-joint motion, may allow for the OmK to provide a more global evaluation of lower extremity kinetics during seated concentric-extension, eccentric-flexion exercise.     

Isokinetic peak torque and hamstring/quadriceps ratios in young basketball players. Effects of age, velocity, and contraction mode

AIM: The purpose of this study was to provide an extensive isokinetic profile, including peak torque and "functional" and "conventional" muscle group ratios, of basketball players throughout the developmental years 12-17. Furthermore, we investigated the effects of age and angular velocity on peak torque and reciprocal muscle group ratios, and observed the force-velocity pattern. METHODS: Basketball players (n=180) 12 to 17 years. were divided according to their age in 6 equal (n=30) groups aged 12, 13, 14, 15, 16, 17 years. All subjects performed maximum knee extension and flexion efforts at 60 inverted exclamation mark /s and 180 inverted exclamation mark /s angular velocities under eccentric and concentric conditions. The absolute (Nm) peak torque was measured, and the relative peak torque (PT/BW) and "functional" and "conventional" reciprocal muscle group ratio (%) were calculated. RESULTS: PT/BW values of knee flexors ranged from 0.98 to 2.29 Nm/kg and of extensors from 1.53 to 3.69 Nm/kg, across all age, velocity, and muscle action levels. PT/BW was higher at slow speed and during eccentric contraction irrespective of age and angular velocity/muscle action. The results indicated a significant (p<0.05) age-related increase in peak torque independent of changes in BW. The force-velocity patterns were similar across ages. The "functional" and "conventional" ratios were not affected by age, but increased with increase in angular velocity, except the CON(KF)/ECC(KE) ratio that was higher (p<0.05) at slow speed. CONCLUSION: The present study provides an extensive isokinetic profile of a knee joint in basketball players throughout developmental years 12-17. Coaches and physical therapist may use these information when evaluating and planning exercise programs during training and rehabilitation.     

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.