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BACKGROUND: It is important for clinicians and researchers to perform dynamic postural control evaluation for predicting musculoskeletal conditions, injury prevention, and rehabilitation. OBJECTIVE: The purpose of this study was to investigate the relationship (1) between the eccentric strength of the knee extensors and star excursion balance test (SEBT), and (2) between the knee proprioception and SEBT. METHODS: Forty healthy young adults participated in this study. The eccentric peak torque (EPT) of the knee extensors, joint position sense, and force sense were measured. The participants also performed SEBT. Pearson’s product-moment correlation and multiple linear regression analysis were used to determine the relationship between the variables and SEBT. RESULTS: The posteromedial direction of the SEBT was positively and strongly correlated with EPT (r= 0.74, P< 0.01). The anterior and posterolateral directions were positively and moderately correlated with EPT (r= 0.46, P< 0.01, and r= 0.69, P< 0.01, respectively.). However, knee proprioception was not correlated with all the directions of SEBT (P> 0.05). According to the results of multiple linear regression analysis, EPT of the knee extensors significantly predicted SEBT reach distances. CONCLUSION: The eccentric strength of the knee extensors seems to be an essential factor in dynamic postural control. However, the knee proprioception did not show a significant correlation with SEBT.

BACKGROUND Traditional Tai Chi is too complex for most elderly individuals. There have been few reports regarding the development of simplified Tai Chi programs to suit the physical needs of elderly adults. However, these programs were not individualized according to the participants' balance control abilities. OBJECTIVE Purpose of this study is to develop an individualized Tai Chi program and report the feasibility of the program. METHODS Phase 1: Five Tai Chi masters performed the Tai Chi movements on a force platform. Based on the results of center of pressure displacement and the individual's balance abilities, an individualized program was developed.Phase 2: Ten community-dwelling older adults received 24 half-hour-sessions, using the individualized Tai Chi exercise program. The Berg Balance Scale (BBS) score, Timed Up & Go (TUG) test, forward reach, and strength of the knee extensor were determined before and after intervention. RESULTS Participants achieved improved performance on balance control as measured with BBS (p≤0.001), TUG (p = 0.004) and forward reach (p = 0.035) as well as knee extensor strength (p = 0.002) after the program. CONCLUSIONS This preliminary result suggests that the individualized Tai Chi program is potentially effective to improve balance function and knee extensor strength of the elderly.

BACKGROUND: To improve walking in persons with multiple sclerosis (MS), it is essential to understand the underlying mechanisms of walking. This study examined strategies in net joint power generated or absorbed by hip flexors, hip extensors, hip abductors, knee extensors, and plantar flexors in mildly disabled persons with MS and healthy controls at different walking speeds. METHODS: Thirteen persons with MS and thirteen healthy controls participated and peak net joint power was calculated using 3D motion analysis. RESULTS: In general, no differences were found between speed-matched healthy controls and persons with MS, but the fastest walking speed was significantly higher in healthy controls (2.42 m/s vs. 1.70 m/s). The net joint power increased in hip flexors, hip extensors, hip abductors, knee extensors and plantar flexors in both groups, when walking speed increased. Significant correlations between changes in walking speed and changes in net joint power of plantar flexors, hip extensors and hip flexors existed in healthy controls and persons with MS, and in net knee extensor absorption power of persons with MS only. CONCLUSION: In contrast to previous studies, these findings suggest that mildly disabled persons with MS used similar kinetic strategies as healthy controls to increase walking speed.

Introduction Kinesio taping consists of the attachment of a thin elastic tape over specific muscles, the thickness of which is similar to that of the epidermis. Objective The aim of the present study was to compare the effect of Kinesio taping and placebo taping on muscle torque, muscle activity and jumping performance soccer players. Methods Thirty athletes were randomly allocated to two groups (Group A: Kinesio taping and Group B: placebo taping). The participants were instructed to perform the Hop test's and were submitted to an isokinetic evaluation of the knee extensors as well as an electromyographic evaluation of the retus femoris muscle of the dominant lower limb. Next, Kinesio taping was performed for the activation of the rectus femoris muscle in Group A and placebo taping was performed in Group B. The participants were reevaluated 30 minutes after taping and 24 hours after the first evaluation using the same tests. Intra-group and inter-group comparisons were made considering the three evaluation times. Results No statistically significant differences were found between groups at any evaluation time regarding the Hop test's, root mean square of the electromyographic signal or peak torque of the knee extensors of the dominant lower limb (p>0.05). Conclusion Kinesio taping for the activation of the rectus femoris muscle has no effect on peak muscle torque, muscle activity or jumping performance among soccer players.

BACKGROUND: Pre-exercise stretching is a commonly used practice by many competitive and recreational athletes. However, the effects of stretching on muscle performance are still incongruous. Furthermore, there is conflicting evidence regarding the intensity of stretching and the effect it has on muscular strength. OBJECTIVE: To investigate the effects of two different intensity levels of passive static stretching protocols on concentric knee extension strength. METHODS: Twenty-two male recreational athletes involved in regular resistance training programs were evaluated using a randomized design. Subjects performed an isokinetic test of the knee extensors following either maximal intensity static stretching, submaximal intensity static stretching, or no stretching. RESULTS: The only significant difference in the peak moment, amounting to 10.5%, was noted between maximal intensity stretching and no stretching. CONCLUSION: Maximal intensity stretching of the quadriceps may adversely affect the acute concentric moment production capacity of these muscles.

OBJECTIVE: To investigate the influence of two different active ankle positions during training on the strengths of knee extensors and flexors. METHODS: A sample of 21 healthy adults was randomized into ankle dorsiflexion (AD, N = 11) and ankle plantarflexion (AP, N = 10) training groups. Subjects were trained isokinetically and concentrically in knee extension and flexion under these two actively fixed, contracted ankle conditions, four times a week for three weeks. RESULTS: AD group showed significant strength improvements in both peak moment and total work. These improvements were also higher significantly, between 29–59% compared to those gained by AP group. CONCLUSION: Active ankle dorsiflexion during concentric isokinetic knee strength training may be more efficient for improving knee extensors and flexors strength than a plantarflexed position.

BACKGROUND AND OBJECTIVE: Muscle strength imbalance can be an important factor in hamstrings muscle strain. The main purpose of this study was to investigate the effects of downhill running on hamstrings/quadriceps torque (H/Qtorque) and the electromechanical delay (H/QEMD) ratios. METHODS: Fifteen active male individuals performed two maximal voluntary isometric contractions of the knee extensors and knee flexors, from which the maximal muscle torque, EMD and H/Qtorque and H/QEMD ratios were extracted. Thereafter, the participants performed a 30-minute downhill run (−16%) at 70% VO2max. Dependent variables were assessed immediately before, immediately following and 48 hours after the effort. RESULTS: Maximal isometric torque decreased significantly immediately after the downhill run for both the extensors (pre: 271.8 ± 45.9 N·m; post: 235.5 ± 55.7 N·m) and flexors (pre: 112.2 ± 26.3 N·m; post: 97.7 ± 27.2 N·m). No significant difference was identified over time for the EMD of the vastus lateralis and biceps femoris muscles. The H/Qtorque and H/QEMD ratios were not influenced by the downhill run. CONCLUSION: We have demonstrated that moderate intensity and volume downhill run does not impair knee joint stability at early (H/QEMD) and late phases (H/Qtorque) of quadriceps/hamstrings contraction.

BACKGROUND AND OBJECTIVE: Proprioceptive information from muscle receptors is important in force control and disturbed sensation due to fatigue may reduce the precision of force control. The aim of this study was to clarify the relationship between force sensation and force control ability in knee extensor muscles during fatigue. METHODS: Eighteen healthy young volunteers participated in this study. Force matching tasks with and without feedback were performed immediately before and after the fatigue protocol consisting of 20 s isometric contractions. The target force was 10% and 30% of the maximal voluntary contraction force in the pre-fatigue protocol. The accuracy of force control ability was estimated by the root mean square error (RMS error) and average difference (average error) between the target and output force. Surface electromyograms were recorded simultaneously from the quadriceps. RESULTS:In the 30% task, there was a significant interaction effect of fatigue and feedback condition in RMS error and average error. RMS error and average error were degenerated significantly by fatigue in the feedback removal condition, but not in the feedback condition. Though the activation of quadriceps was increased by fatigue, increase of muscle activation was lower in the feedback removal condition than that in the feedback conditions. CONCLUSION: Since participants controlled their force output depending on the force sensation in the feedback removal condition, these results indicate that the decline in force sensation may be a significant factor in the decreases of accuracy in force output during fatigue.

BACKGROUND: Although resistance training adaptations in multiple sclerosis (MS) patients have been described, the detraining response in this population is largely unknown. OBJECTIVE: This study was designed to evaluate the effects of a 12-week detraining period on muscle strength (isometric and endurance) and muscle power of multiple sclerosis (MS) patients that had previously carried out a 12-week resistance training program (RTP). METHODS: Forty-two MS patients were randomly assigned into two groups: an exercise group (EG) that performed a 12-week RTP for the knee extensors muscles; and a control group (CG), that did not perform any specific training. Knee extension maximal voluntary isometric contraction (MVIC), muscle power and muscle endurance were evaluated before and after the RTP, as well as 12 weeks after training completion. A strain gauge was used to measure the maximal voluntary isometric contraction and muscle power was assessed with a linear encoder. Muscle endurance was interpreted as the number of repetitions that a patient could perform in a single set of knee extension exercise. RESULTS: The EG increased MVIC and muscle power after the training period, although the training did not affect muscle endurance. After 12 weeks of detraining, MVIC returned to pre-training values but muscle power was still greater than pre-training values in the EG. The CG did not present any change in the variables measured during the intervention. CONCLUSIONS: A 12-week RTP improved MVIC and muscle power in MS patients. Additionally, 12 weeks of detraining blunted strength training adaptations in MS patients, although muscle power training adaptations were still evident after the detraining period.

BACKGROUND: Few studies have assessed the test-retest reliability of the isokinetic strength at 90 ◦ /s and the isometric parameters for knee extensors. OBJECTIVES: To assess the reliability of isokinetic and isometric parameters of knee extensors, and to determine the smallest real difference between the test-retest measures. METHODS: Knee extensor strength was measured twice, 4 to 5 days apart, using a Biodex dynamometer in forty subjects (12 men, 28 women). The protocols consisted of 5 concentric contractions at 90 ◦ /s and 5 isometric contractions. RESULTS: For women, test-retest reliability was very high for isometric and isokinetic peak-torque (ICCc,1 > 0.9 ), moderate for work (ICCc,1 = 0.82) and questionable for angle of peak torque (Angle-PT), mean Angle-PT and rate of torque development (RTD0−100 ms) (ICC < 0.67). The measurement errors were small for all variables, the SEM% ranged between 3.1% to 7.4%, and SRD% from 8.6% to 19.9%, except for RTD0−100 ms that was the most variable (SEM% = 16.4%; SRD = 47.5%). No differences were found in Angle-PT and RTD0−100 ms with regard to sex. CONCLUSIONS: The isokinetic values obtained at 90 ◦ /s and isometric peak-torque for knee extensors are highly repeatable with a standardized test protocol and the SRD values can be used to detect real changes. Alternative strategies of analysis should be developed to improve reliability of Angle-PT and RTD0−100 ms. Angle-PT and RTD0−100 ms do not appear affected by gender

BACKGROUND: Team sport athletes require dynamic stability in unilateral activities for their sports, which necessitates some degree of knee flexion and extension strength. OBJECTIVE: To analyze the possible association of knee extension and flexion strength with dynamic stability, as measured by the Star Excursion Balance Test (SEBT). METHODS: Sixteen male team sport athletes completed the SEBT, which involves a series of unilateral squats with the subject maximally reaching with the other leg in eight directions. Knee muscle strength was measured isokinetically both concentrically (60 ◦ /s, 180 ◦ /s, 240 ◦ /s) and eccentrically (30 ◦ /s). Subjects were divided into better and lesser groups based on mean functional reach distance. A 1-way analysis of variance (p 0.05) determined between-group differences in reach distances and relative torque. RESULTS: Subjects with better dynamic stability generated greater knee extensor torque concentrically at 180 ◦ /s for the right leg, and at all speeds for the left leg. The effects of knee strength were particularly noteworthy for the left leg, as subjects with better dynamic stability reached significantly further across all 8 directions. CONCLUSION: The results indicate that greater knee extensor strength may enhance unilateral dynamic stability in team sport athletes.

BACKGROUND: There are alterations in strength in relation to menstrual cycle phase but little data attributing these responses to female sex hormone levels using a pseudo-menstrual cycle group as control. OBJECTIVE: Examining the effects of menstrual cycle phase on the development of peak torque across a range of isokinetic speeds. METHOD: 17 well trained females, 11 formed the non-oral contraceptive group (n-OC) (age 20.7 ± 1.4 yrs, mass 59.2 ± 6.9 kg, height 166.8 ± 7.1 cm) and 6 the oral contraceptive control group (OC) (age 20.3 ± 0.5 yrs, mass 60.5 ± 4.2 kg, height 164.8 ± 4.8 cm). Concentric strength of the knee flexors and extensors (60–240°/s) was assessed, corresponding to menstruation (MEN), mid-follicular (mFOL), mid-luteal (mLUT) and pre-menstrual (pMEN). RESULTS: For n-OC significant decreases in peak torque production of the extensors at 120°/s (P=0.0207) (MEN) and of the flexors at 60°/s (P=0.0116) (MEN) and 120°/s (P=0.0282) (MEN) were observed compared to pMEN. No significant differences were observed across any menstrual cycle phase and peak torque for the OC group (p> 0.05). Significant positive correlations were observed (mLUT) between peak torque and oestrogen at 60°/s (P=0.040) and 120°/s (P=0.031). CONCLUSIONS: There are significant fluctuations in peak torque of the knee extensors in response to phases of the menstrual cycle associated with variances in the female sex hormones. The findings have implications for the planning of strength training in female athletes.

The greater torque generation capacity of muscles when contracted alone than in combination with contralateral muscles, characterizes the bilateral limb deficit (BLD) phenomenon. Few studies have explored the BLD in dynamic movements, because isometric actions are considered ideal for evaluating strength. Therefore, the aim of this study was to compare BLD between isometric and concentric actions of the knee extensors. Eleven healthy young men (age = 20.6 ± 1 yrs; weight = 71.4 ± 6.4 kg; height = 174.4 ± 7 cm) volunteered to participate. Initially, subjects visited the laboratory for familiarization with the test protocols. On two subsequent randomized days they performed a test protocol with either a unilateral (right and left limbs) or bilateral condition, with 48 h rest between. The test protocol was composed of five isokinetic concentric actions of the knee extensors at 60 ◦ /s and three isometric actions at a 60 ◦ angle of knee flexion. The greatest peak torque of the two conditions was used for analyses. Both muscle actions demonstrated greater values unilaterally ( p 0.05). Therefore, if muscle torque production is greater unilaterally, athletes and coaches may utilize unilateral exercises to increase training loads.

OBJECTIVE: To determine the applicability and predictive accuracy of an isoinertial resistance machine for the assessment of hamstring/quadriceps conventional (concentric) ratio (CR). METHOD: Thirty-two resistance trained young men (23.53 ± 3.2 yrs) were tested using dedicated instruments to obtain the peak torque (PT) of the right knee extensors and flexors as well as the corresponding one repetition maximum (1RM) values. All measurements were conducted in the concentric mode. RESULTS: Significant (p< 0.05) correlations were indicated between knee extensor and flexor PT and 1RM values (r=0.73 to 0.75), as well as between PT and 1RM CR values (r=0.65). However the isoinertial CR values (0.42 ± 0.05) were significantly (p< 0.05) greater than their isokinetic counterparts (0.36 ± 0.04). CONCLUSION: Caution should be used when comparing isoinertial CR with population-specific isokinetic normative scores.

The effect of contraction intensity (100%-, 75%-, 50%-, and 25%-maximum voluntary contraction (MVC)) and movement velocity (0 ◦ , 100 ◦ , 200 ◦ , 300 ◦ , and 400 ◦ /s) on the root mean square amplitude (SEMG-RMS) and median frequency power spectrum (SEMG-MPF) of the surface electromyography of the vastus medialis (VM) and rectus femoris (RF) muscles during isokinetic extension movements was investigated. Eight healthy female university students (age = 23.1 ± 2.6 yrs., mean height = 161.8 ± 6.8 cm, mean weight = 64.6 ± 6.1 kg) with no known knee pathologies participated in the study. Peak moment (PM), SEMG-MPF, and SEMG-RMS were analyzed using separate repeated measures analysis of variance (ANOVA). Results indicated (p 0.05): (1) an inverse relationship between PM and movement velocity, which was consistent with the literature and the force-velocity curve; (2) an increase in VM and RF SEMG-RMS across all isovelocity movements compared to isometric, with highest values occurring at 200 ◦ /s; (2) a linear increase in SEMG-RMS as force levels increased from 25%-MVC to100%-MVC; and, (3) an increase in SEMG-MPFvalues during isovelocity movements compared tothat found during isometric contractions, with highest values at 50 ◦ /s, suggesting isovelocity movements facilitated a greater recruitment of fast-twitchfibers. It appears that the degree to which the central nervous system activates muscle is based on the interplay of both contraction intensity and velocity needed to complete the required motor task.

This study aimed at quantifying maximal voluntary force-generating capacity of the quadriceps femoris and its EMG output after an isokinetic concentric intermittent exercise. Another objective was to find out whether the amount of neuromuscular fatigue was velocity-dependent. Eight males judo players (age: 18.4 ± 1.4 years; height: 1.80 ± 0.03 m; body mass: 77.0 ± 4.2 kg) performed a fatiguing exercise composed of five sets of ten maximal knee extension at 120°/s, with 3min recovery in between. Peak torque (PT) at three angular velocities (60, 120 and 180°/s) and EMG from the vastus lateralis, rectus femoris and vastus medialis were evaluated before and after the fatiguing exercise. EMG was analyzed for root mean square (RMS) and median frequency (MF). The fatiguing exercise induced PT decrement (P< 0.01) irrespective of the test velocity, in conjunction with decreased RMS (P< 0.001) and a decrease in MF (P< 0.01). In addition, although EMG activity demonstrated no velocity effect, the loss of PT after the fatiguing isokinetic intermittent exercise was more pronounced at the lower velocity (P< 0.05). The combination of decreased PT, RMS and MF suggests a reduction of the neural drive under the present fatiguing protocol.

Although previous studies have demonstrated that skeletal muscle adaptations were specific to the types of stimuli, eccentric training studies presented controversial results concerning strength gains in eccentric, isometric and concentric tests. Therefore, the goal of this study was to evaluate torque-velocity adaptations following isokinetic eccentric training protocol using the quadriceps as a model. Twenty physically active men were randomly assigned to a control group (CG; n = 10) or to an eccentric training group (ETG; n = 10). Knee extensor torque-velocity relationship including isometric tests and isokinetic tests at 60 ◦ /s, 120 ◦ /s, 180 ◦ /s, 240 ◦ /s and 300 ◦ /s in concentric and eccentric modes, were assessed before and after a 12-week period of eccentric training (3 sessions/week; 2-5 sets of 7-9 maximal repetitions per session performed at 60 ◦ /s along a range of motion 90 ◦ ). Isokinetic eccentric training significantly increased the knee extensor torque at the training velocity (59%) and at the adjacent velocities (24% at 120 ◦ /s and 29% in the isometric test). These results demonstrate the specificity of strength gains

This study investigated knee extensor muscle strength, work and fatigue level under maximal isokinetic concentric and eccentric exercise. Seventeen male athletes were randomized into two groups and performed 10 sets of 10 maximal isokinetic concentric (N = 8) or eccentric (N = 9) contractions. Knee extensor peak torque and mean torque values per set were 54-121% and 53-133% higher in eccentric compared to concentric exercise, respectively, whereas the percent fall of performance in these variables was more accentuated in concentric exercise. Total work was significantly higher in eccentric exercise (19475 J) than concentric exercise (15758 J), while fatigue index was greater in concentric (36%) than eccentric (18%) exercise. In conclusion, maximal isokinetic eccentric exercise promotes larger overload to knee extensor muscles than its concentric counterpart due to higher torque produced by the muscle group and also thanks to minor muscle fatigue effects.

The vast majority of previous research with isokinetic machines has used only ascending or random velocity sets during testing. The purpose of this study was to investigate the effect velocity order (ascending vs. descending order) had on peak torque of knee extension during isokinetic testing and to examine the differences in peak torque in collegiate and recreational athletes. Thirty healthy, college aged males (15 collegiat e athletes (CA): mean Age 20.27 yrs, Ht 178.99 cm, Mass 85.00 kgs and 15 recreational athletes (RA): Age 21.2 yrs, Ht 183.39 cm, Mass 89.06 kgs) performed two familiarization trials and four randomly assigned experimental trials. Subjects performed four knee extension repetitions at five velocities in eithe r ascending (60, 120, 180, 240, and 300 � /sec) or descending (300, 240, 180, 120, 60 � /sec) order. There was no significant ( p < 0.05) difference between the order of velocities and peak torque or between CA and RA groups. Although not statistically significant, RA produced greater peak torque than CA. This may be a result of numerous RAs in this study being former collegiate athletes. In conclusion, the order of velocities may not be pertinent when establishing a protocol for testing peak torque of the knee extensors in healthy college-aged males.

Isokinetic assessment of knee extensors muscle group function in patients suffering from knee osteoarthritis has exclusively been achieved using time-domain based variables. While useful, these analyses do not quantify the conspicuously irregular moment-time pattern exhibited by the involved knee when compared to the contralateral knee. The purpose of this investigation was to assess whether the frequency content of the isokinetic curve can quantify this latter phenomenon. Thirty two patients with knee osteoarthritis participated in this study. Each participant performed 5 maximal concentric knee extensions bilaterally at 60 � /s using an isokinetic dynamometer. For each time-domain extension curve, the power spectrum was calculated via Fast Fourier Transform and the maximum frequency content value contained within 99% of total signal power was extracted. Of the 32 participants, 26 exhibited higher frequency contents in the isokinetic curves obtained from their involved knee (p = 0.002, effect size = 0.35). The results suggest that the frequency content of iso kinetic moment-time curves may provide useful quantitative information regarding the smoothness of moment production, and as such, may be used in conjunction with traditional time-domain variables in the assessment of knee extensors function in patients suffering from knee osteoarthritis.

The purpose of this study was to examine the within-day and between-days reproducibility of isokinetic parameters of knee, shoulder and trunk movements. Ten healthy males (age 30 ± 8 years, height 1.79 ± 0.05 m, body mass 79.4 ± 8.3 kg) performed isokinetic concentric contractions (knee: 60 and 180 ◦ /s; shoulder: 60 and 180 ◦ /s: and; trunk: 15 and 60 ◦ /s) at 0 (baseline), 2, 24, 48 and 72 hours. Reproducibility of the baseline peak moment, mean peak moment and maximum work was assessed using Bland and Altman limits of agreement and pre-planned paired t-tests ( P< 0.05). Peak moment of knee, trunk and shoulder extensors at low velocities had highest reproducibility within and between days over a time period of 3 days. Peak moment at high and low velocities of knee extensors was consistently the most reliable parameter over a 3 day period. It is concluded that isokinetic parameters can be reproducibly measured in a combined session of knee, shoulder and trunk movements in healthy male subjects over a 3-day time period.

The purpose of this study was to determine the effect of single sets vs. multiple sets on different muscle groups peak torque (PT) in untrained subjects. Twenty four untrained males were randomly assigned into one of two groups: 1) knee extension three sets and elbow flexion single set (3K-1E; n = 11), or 2) knee extension single set and elbow flexion three sets (1K-3E; n = 13). Subjects trained 2 days/week for 6 weeks and each workout consisted of 1 leg press exercise and 1 barbell curl. Training intensity started at 8 repetition maximum (RM). Strength was expressed as a concentric PT at 60 ◦ /s. ANOVA revealed that the increase in PT of the knee extensors from week 0 to 6 was significantly greater in the 3K-1E group (11.5%) than in the 1K-3E (4.0%) group, while no difference existed in the PT gains of the elbow flexors between 3K-1E (9.2%) and 1K-3E (7.8%). It was concluded that performing three sets of strength training is superior to one set for increasing strength of the knee extensors while single-set training protocols for the elbow flexors might be sufficient for untrained individuals in the early phases of a strength-training program.

The purpose of the study was to identify both demographic and neuromuscular traits that characterize successful or unsuccessful adaptation to resistance training in older women. Twelve, older women underwent electrically evoked muscle twitches for the knee extensors; and performed maximal, voluntary, isometric knee extensions, followed by eight weeks of resistance training. Prior to training nonresponders had 67% higher twitch peak torque than responders (0.29 ± 0.05 vs. 0.18 ± 0.06 Nm·kg -1 respectively), 64% higher twitch rate of torque development (RTD) (3.96 ± 0.47 vs. 2.42 ± 0.62 Nm·s -1 ·kg -1 ), 51 % higher voluntary peak torque (1.86 ± 0.40 vs. 1.23 ± 0.33 Nm·kg -1 ), 101 % greater RTD (9.43 ± 1.52 vs. 4.70 ± 2.40 Nm·s -1 ·kg -1 ), 86% greater impulse (0.13 ± 0.01 vs. 0.07 ± 0.03 Nm·s·kg -1 ) and 27% faster motor time (80 ± 13 vs. 109 ± 34 ms), (all P < 0.05). Following training, responders showed an 11 % increase in twitch peak torque over baseline (0.18 ± 0.06 to 0.20 ± 0.05 Nm·kg -1 ), 15% increase in voluntary peak torque (1.23 ± 0.33 to 1.41 ± 0.36 Nm·kg -1 ), 47% increase in RTD (4.70 ± 2.40 to 6.93 ± 2.02 Nm·s -1 ·kg -1 ), 43% increase in impulse (0.07 ± 0.03 to 0. 10 ± 0.04 Nm·s·kg- 1 ), and 26% increase in rate of EMG rise (886 ± 214 to 1116 ± 102% pEMG·s -1 ) (all P < 0.05). Initially higher muscle mass and contractility, coupled with greater neural drive, likely explains why older women with good muscle performance seem to have a lower capacity for improvement than women with low initial levels of performance.

The mechanisms underlying age-related differences in maximum power production during multi-joint exercises are not fully understood. One factor that could contribute to these age-related differences is a differential development of the ability to generate maximum strength and power across the involved joints. Therefore, the purpose of this study was to investigate the age-related changes in knee extensor and plantarflexor strength under isometric and isokinetic conditions. Ten boys (11.6 ± 0.8 yrs) and 10 male adults (27.7 ± 5 yrs) participated in the study. Ankle plantarflexion and knee extension strength were measured isometrically and isokinetically at 30, 75 and 120°/s. Muscle activity (EMG) from the Gastrocnemius Medialis and Vastus Lateralis was also recorded. Multivariate analyses of variance identified significant Age by Joint interactions for isometric peak torque (PT) and isokinetic peak joint powers for all conditions (p 0.05). Our results suggest that the development of lower limb isometric strength is joint-dependent and that this joint dependence is not due to a muscle-specific development of motor unit recruitment.

8th World Congress of Performance Analysis of Sports -- SEP 03-06, 2008 -- Magdeburg, GERMANY, WOS: 000267950800005, The purpose of this study was to investigate the relationship between isokinetic strength of knee, vertical jump and anaerobic peak power. Twenty one healthy young male voluntarily participated in this study. Squat Jump (SJ), Counter Movement Jump (CMJ) and Wingate anaerobic power test were performed. Bilateral concentric isokinetic strength of the knee extensors/flexors was evaluated at 60, 120 and 180 degrees/s. CMJ height had a significant and moderate relationship with the isokinetic knee strength of extension measured at 120 and 180 degrees/s whereas SJ height was not correlated with any of the isokinetic strength parameters. Absolute, and less so normalized, power bore significant relationship to the isokinetic parameters. Hence the relevance of maximal isokinetic knee extension strength may be limited counter movement jumping.

Shear stress is considered an important stimulus for vascular adaptations with exercise training, yet the shear rate response to exercise has not been carefully examined in women or in healthy older adults. Therefore, the purpose of this study was to determine if age or sex differences are present in common femoral artery (CFA) shear rates during leg exercise. Diameter and mean blood velocity were measured in the CFA using Doppler ultrasound in young (20-30 yr) and older (60-79 yr) men and women at rest and during single-leg knee extensor exercise. Shear rate was calculated. Resting shear rate was lower in older compared to young adults (33.9 ± 3. 7v s. 58.3 ± 3. 6s −1 , respectively; p< 0.05) and lower in men than women (36.8 ± 3. 8v s. 55.4 ± 3. 5s −1 , respectively; p< 0.05). During exercise, older adults had overall lower shear rates compared to young adults (within-sex comparison, p< 0.05). The rise in shear rate with work rate showed no age difference but was lower in men than women (4.6 ± 0. 4v s. 8.6 ± 0. 4s −1 per W, p< 0.05). These results suggest that age and sex differences are present in CFA shear rates during exercise which could have implications for vascular adaptability with exercise training.

The aim of the present study was to examine the acute effect of a brief submaximal percutaneous electrical stimulation (PES) of the knee extensor (KE) muscles as a conditioning activity on the isokinetic peak torque (PT) and average power (AP). Eighteen male students aged 20-25 years performed maximal voluntary concentric isokinetic knee extensions at angular velocities of 60 and 180°/s in control (CON) trial (without prior PES application), followed by a PES trial after 30 min rest period. In PES trial, a conditioning submaximal (25% of the maximal voluntary isometric contraction force) isometric tetanic contraction of the KE muscles was induced by a 7 s direct PES at 100 Hz, interspersed after 3 min with testing of voluntary isokinetic performance. No significant differences in isokinetic knee extension PT and AP were observed between PES and CON trial at 60°/s. However, a significantly greater (p < 0.05) isokinetic PT (8.9%) and AP (8.2%) were observed in PES trial compared to CON trial at 180°/s. In conclusion, application of a brief high-frequency submaximal PES may enhance isokinetic strength and power of the KE at a moderate but not at a low angular velocity.

The purpose of this study was to determine the reproducibility of measures for maximum knee extensor and flexor concentric strength on an isokinetic dynamometer in individuals with mild and moderate osteoarthritis of the knee. Twenty eight female patients with 1 st (n = 14) and 3 rd (n = 14) grade unilateral knee OA volunteered for the study. Peak muscle torque of the knee extensors and flexors was measured using an isokinetic dynamometer at angular velocities of 90, 120 and 150 ◦ /s. Test-retest reproducibility of maximal isokinetic torque was evaluated using intraclass correlation coefficient (ICC). Absolute reproducibility was assessed using Bland-Altman analysis, the standard error of measurement (SEM and SEM%) and the smallest real differences (SRD & SRD%). Inter-session relative reproducibility was found to be high in extensor and flexor muscles of individuals with mild OA, with the ICCs values ranging from 0.89 to 0.92 for the concentric knee extension and from 0.90 to 0.93 for the concentric knee flexion, while in the group of individuals with moderate knee OA the same values varied from 0.79 to 0.91 and from 0.75 to 0.93 for the concentric knee extension and flexion, respectively. The Bland-Altman analyses support the findings of high relative reproducibility for the two groups of patients in almost all measurements, except for the extension at 120 and 90 ◦ /s and the flexion at 150 ◦ /s conducted by the individuals with moderate OA. SEM and relative SEM values ranged from 6.7 to 9.4 Nm and from 14.4% to 21.5%Nm for the group with mild OA and from 4.4 to 7.7 Nm and from 14.6% to 21.8%Nm for the group with moderate OA, respectively. SRD and SRD% values across all movement speeds for both knee flexors and extensors ranged from 18.6 to 26.1 Nm and from 39.9% to 59.6%Nm for the mild OA group, respectively, while the same values for the moderate OA group ranged from 12.2 to 21.3 Nm and from 40.5% to 56.8%Nm, respectively. These results indicate that measurements of isokinetic performance at velocities of 90, 120 and 150 ◦ /s provide acceptable reproducibility for evaluation of knee strength in individuals with mild OA of the knee. On the other hand, with regard to knee muscles isokinetic performance, testing of individuals with moderate OA should be conducted during periods of time when the symptoms of the disease subside.

Warm-up and stretching exercises constitute an essential part of physical preparation before any athletic event. The aim of this study was to examine the acute effect of static and dynamic stretching exercises on maximal isokinetic torque of knee extensor and flexor muscles. Thirty-two (n = 32) physical education students aged 19-22 years were asked to perform three different protocols consisting of A) warm-up, B) warm-up and static stretching and C) warm-up and dynamic stretching exercises, on three non-consecutive days. Each treatment was followed by measurements of knee extensor and flexor muscles maximal concentric torque on an isokinetic dynamometer at 60 and 180 ◦ /s. ANOVA for repeated-measures revealed significant differences in maximal torque following the different protocols. Tukey's post hoc tests showed a reduced torque for knee extensor ( p< 0.01) and knee flexor muscles ( p< 0.01) at both velocities when static stretching exercises preceded the test. These findings indicate the negative influence of the static stretching exercises on maximal isokinetic torque production, while dynamic stretching approach does not seem to have any inhibitory effect.

The purpose of this study was to document age-related alterations in trunk extensor strength and to compare these to changes in knee extensor strength over varying angles of muscle contraction. A secondary purpose was to compare age-related changes in trunk extensor endurance while statistically correcting for torso mass differences. Eighteen older (70 ± 7.3 years) and fifteen younger (22.1 ± 4.6 years) women volunteered for the study. Torso mass and trunk extension endurance (Modified- Sorenson test) were also evaluated. The results suggested that age-related torque production was both angle and muscle group dependent. Younger adults were 29% stronger in the knee and 23% stronger in the trunk extensors. Furthermore, the difference between age groups in knee extensor strength was 2.30 Nm/kg at 78 ◦ , but only 0.47 Nm/kg at 6 ◦ of knee flexion. This angle discrepancy was not evident in the trunk extensors. Following torso mass correction, trunk extension endurance time did not differ between ages (Young: 160.4 ± 65.8 vs. Old: 159.5 ± 71.9 sec, p = 0.99). Our study suggests that the elderly should focus on improving trunk extension strength rather than endurance. Also, knee extensor strength exercises should be emphasized between 60 ◦ and 108 ◦ of knee flexion in the elderly to combat the age-related loss of lower extremity strength.

The aim of the study was to determine knee muscles absolute and relative strength and power, as well as flexor/extensor (F/E) ratios, in prepubescent male and female swimmers, during concentric isokinetic testing. Twenty boys and 20 girls, aged 10-12 years, participated in this study. Gravity corrected concentric isokinetic peak torque (strength) and average power (power) were measured by a Cybex Norm dynamometer at the angular velocities of 60, 120 and 180 ◦ /s, during unilateral knee extensions and flexions. The relative values of strength and power were expressed per kilogram of lean body mass. Knee extensors strength and power do not differ significantly between boys and girls at the angular velocities of 60 and 120 ◦ /s. In contrast, at the higher angular velocity of 180 ◦ /s boys exerted greater values than girls ( p< 0.01). With respect to the knee flexors, boys exerted greater values than girls only at the angular velocities of 120 and 180 ◦ /s ( p< 0.01). When relative strength and relative power were calculated, no significant differences existed between boys and girls for both muscle groups. Moreover, the shapes of strength-velocity and power-velocity curves, as well as knee F/E ratios, were similar for both groups.

The aim of the present study was to determine the relationship between vertical jump performance and the isokinetic strength of the knee extensors in professional soccer players at the end of the of the competition period, after the detraining period (before the initiation of the preparatory period) and after the completion of the preparatory period. Eighteen professional soccer players participated in the present study. The peak jumping height (of the squat and counter movement jumps on an Ergojump device) was used as indicator of vertical jump performance. The subjects also performed three submaximal and three maximal isokinetic efforts of the knee extensors at angular velocities of 60 and 180 ◦ /s. Pearson product moment correlation analyses were conducted to determine the relationship between isokinetic strength and jumping parameters. The significance level was set at p< 0.05. The analysis indicated that jumping height was moderately correlated with the knee torques at the test velocities after the competition and preparatory period.

Manual massage is considered an important part of athletic rehabilitation or preparation for training and competition. Objective: To study the possible effects of manual massage on concentric and eccentric peak torque of knee extensors, when applied during intervals of exercise. Methods: Twelve elite female Tae Kwon Do athletes were tested twice during a week (different extremity each) in continuous concentric/eccentric isokinetic exercise (6 sets of 10 repetitions, with 2 minutes intervals). Manual massage was applied during breaks to the extremity (massage extremity) while for the other limb (control extremity) the interval was passive. For both groups peak torque was measured 3 minutes after the last set. The same test was performed 3 minutes prior to the first set. The best performance was recorded pre- and post-exercise and the results were compared. Results: For both groups peak torque (concentric and eccentric) was reduced after the exercise protocol. In the massage group the reduction was lower and significantly different for eccentric type of muscle work ( p< 0.05). Conclusions: Application of manual massage during isokinetic exercise intervals has an enhancing effect on the peak eccentric torque of the knee extensors.

In a previous study, balance training yielded a gain in strength in middle-aged men and women [6]. However, whether such training can yield positive results in highly conditioned athletes has not been addressed. A group of 10 male and 10 female judokas volunteered for a 6-week balance training on rolling boards, pegtops, soft mats and large rubber balls 3 times per week. Pre- and post training of two-legged balance was measured on a stabilometer, one-legged standing time on a narrow rim and bilateral isokinetic strength at 60°/s concentric and eccentric modes, 120°/s concentric mode and isometrically for the knee extensors and flexors. Except for concentric movement at 60°/s in women, significant improvements in strength were indicated. It is therefore concluded that balance training may be useful for both male and female judokas for increasing strength and balance.

This study investigated the effects of isotonic and isometric knee extension exercises on strength, power, and surface EMG in male and female populations. Using the knee extensors, ten males and ten females performed a 120 s MVIC and 120 maximal isotonic contractions. Prior to each exercise (t = pre) knee extensor isometric peak torque (strength) and average peak power (power) were tested utilizing three, 3 s MVIC’s and three maximal isotonic contractions, respectively. Following each exercise, strength and power were assessed immediately after (t =: 00) and at 2.5 (t =: 02.5), 5 (t =: 05), 10 (t =: 10), and 15 (t =: 15) minutes. All strength and power measures were normalized to the respective t = pre value. Vastus lateralis surface EMG signals were collected during all muscle testing and normalized to the respective tire value. Following isometric exercise, both strength and power at t =: 00 (68.7% ± 8.7% & 88.0% ± 8.7%) and t =: 02.5 (82.2% ± 17.8% & 95.2% ± 5.0%) significantly decreased from t=pre (100% ± 0.0%) (p < 0.05) with greater decreases in strength at each time point (p < 0.05). EMG analysis revealed a significant EMG amplitude decrease (p < 0.05) at t =: 00 and t =: 02.5 during strength testing with respect to t=pre. Following isotonic exercise, both strength and power at t =: 00 (68.0% ± 13.2% & 38.8% ± 10.7%) and t =: 02.5 (84.5% ± 14.9% & 81.6% ± 14.5%) significantly decreased from t=pre (100% ± 0.0%) with a greater power decrease at t =: 00 (p < 0.05). The EMG amplitude of males was significantly less at t =: 00 than the respective EMG amplitude for females (p < 0.05) (irrespective of testing condition). We conclude that muscle performance in the fatigued state is dependent upon the type of exercise performed.

The purpose of this study was to analyze the isokinetic moment curve (IMC) of the knee extensors after ACL reconstruction using a qualitative approach. Fourteen professional soccer players after ACL reconstruction participated in this study. All subjects were free of any clinical symptoms related to the injury or surgery. The concentric strength of knee extensors was measured bilaterally using an isokinetic dynamometer. Each subject was tested twice, before and after 3 weeks of isokinetic training. For each test, the IMCs of the knee extensors were analyzed by two examiners. The examiners were asked to differentiate between the involved and uninvolved side and classify the IMC of the involved side. The results indicate that a qualitative analysis of the shape of IMC is a valuable tool for patient evaluation and rehabilitation.

The purpose of this study was to examine the relationship between vertical jumping performance and isokinetic moment of force of knee extensors, hip extensors and ankle plantar flexors in adult males. Twenty-nine males performed squat and counter movement jumps on an Egrojump device. The peak jumping height and the total work (height x body mass) were used as indicators of vertical jump performance. The subjects also performed three submaximal and three maximal isokinetic efforts of the hip extensors, knee extensors and ankle plantarflexors at angular velocities of 60, 120 and 180°.s -1 on Cybex Norm Dynamometer. Pearson's product correlation tests indicated that there was a significant (p 0.05). Multiple regression analysis indicated that linear combinations of isokinetic torques accounted for 38% and 42% of the countermovement and squat jumping height variance, respectively. In contrast, regression models using isokinetic torques could predict jumping work accounting for 75% (counter movement jump) and 69% (squat jump) of the variance. The above results indicate that there is a moderate to high relationship between isokinetic knee and hip extension torques and vertical jump performance parameters, especially when jumping height is multiplied by subject's body weight. Furthermore, it appears that when using a linear combination of isokinetic torques from hip and knee joint muscle groups the multiple relationship between isokinetic tests and jumping performance is higher.

This study focused on the design of an isokinetic test protocol for the evaluation of the anaerobic power-capacity ofthe knee extensors and flexors, and its validation using the Wingate 30” anaerobic test. Twenty male track and field, sprint andjumping events athletes aged 17–28 years took part in the study. In the first session evaluation of lower limb anaerobic powertook place. Following 48 hours their knee extensors and flexors were tested isokinetically (30 Reps at 240 ◦ /sec for 30s). Theresults have indicated a very high correlation coefficient r =0 . 927 between the values of the medium power for both tests, whilethe correlation coefficient between the fatigue indexes was relatively low r =0 . 485. Thus isokinetic testing of knee musculaturecould provide a valid measure of the anaerobic capacity of the knee extensors and flexors, particularly with respect to athleteswho perform through the anaerobic glycolitic way. On the other hand, isokinetically-based fatigue could not be compared withthe more common and is therefore not advisable as an alternative indicator to the Wingate test.Keywords: Anaerobic power-capacity, Wingate test, knee muscles

The purpose of this study is to assess the ability of clinicians to identify false isokinetic strength test of the knee flexors and extensors, based only on the shape of the torque curve. The concentric strength was measured bilaterally using an isokinetic dynamometer at 60°/sec. Each subject performed two modes of testing: a) A Genuine strength test (GST) which consisted of five consecutive cycles of knee extension and flexion at maximal effort, b) A false strength test (FST) which consisted of five consecutive cycles of knee extensions and flexion attempting to feign pain. For each test, the torque curves were printed and presented to four judges to mark each of the tests as a GST or a FST based on the shape of the torque curves. The mean percentage of success in identifying a GST and a FST for the 4 judges was 91.9% (range = 87.5-97.5%) and 90.6% (range = 82.5-95%) respectively In conclusion, in spite of the constraints, which were imposed on the judges, the rate of correct classification was high.

Men and women differ in strength according to the muscle mass of knee extensors and flexors. Side differences between left and right are frequently reported. We measured isokinetic strength and balance performance in 7 men and 8 women and calculated side differences before and after 6 weeks of balance training conducted twice a week for 25 min. Before training. extension and flexion strengths were 70% and 72% higher in men compared to women, respectively. After training gain was 12% for both groups. The side differences of 10% in men and 11% in women for extensors and 7.7 and 10% for the flexors were reduced to 1.0 and 0.8% and 2.0 and 1.1%, respectively. All participants improved balance performance in one leg standing time, Men and women with comparable anthropometric data and level of physical activity improved strength by balance training without strength training. This study also underscores importance of balance training as a preventive measure especially in old age.

Purpose: The purpose of this study was to determine if surface electromyography (EMG) could be used to index fatigue during isotonic and maximal voluntary isometric contractions (MVIC) of the knee extensors in men and women. Methods: Ten males (age = 22.1 ± 3.3 yr, ht = 180.3 ± 5.5 cm, mass 78.7 ± 5.1 kg) and ten females (age = 23.9 ± 4.6 yr, ht = 163.7.3 ± 11.1 cm, mass 63.2 ± 7.4 kg) underwent one isometric (120 s MVIC of the knee extensors) and one isotonic (120 maximal effort isotonic contractions at a resistance of 25% of the MVIC peak torque determined on the testing day) exercise session separated by at least 48 hrs. The EMG signal was collected from the vastus lateralis during both exercise protocols using standard EMG collection techniques. Average torque (AT) was calculated from each 3 s window of the 120 s MVIC, and the average peak power (APP) was calculated for every 3 consecutive contractions during the dynamic exercise. Results: Both the isometric and isotonic fatigue protocols resulted in significant (p 0.05). A main effect for gender (p < 0.05) revealed larger EMG amplitude for females when compared to males during isotonic exercise. Conclusions: These results indicate that gender may be a factor in the development of dynamic fatigue and that EMG can index fatigue during a sustained MVIC.