Isokinetic strength testing in patients with chronic heart failure--a reliability study

Measurement of skeletal muscle strength gains increasing importance as outcome parameter in patients with chronic heart failure. This study aimed at establishing short-term reliability of isokinetic strength measurements of knee extensor and flexor muscles in 38 patients with chronic heart failure. Strength tests were performed on the Cybex 6000 dynamometer. Trunk fixation was restricted to pelvic fixation. Two bouts of strength testing were performed on day 1 and one on day 5. Each isokinetic bout consisted of 3 reciprocal knee extension and flexion movements with an angular speed of 60 degrees per second. Isometric strength was measured at 30 degree knee angulation. Intraclass correlations ranged between 0.96 and 0.99 for isokinetic and isometric peak torque of knee extensor muscles and 0.82-0.96 for flexor muscles. Analysis of repeated measurements showed significant differences among the values of flexor peak torque in the isokinetic mode and between all measurements in the isometric mode (p < 0.05). Pearson's correlation coefficients for isokinetic and isometric extensor peak torques ranged between 0.95 and 0.99, for flexor peak torques between 0.81 and 0.85 (all p < 0.0001). Measurement of isokinetic knee extensor and flexor peak torque is a reliable method to assess muscle strength in patients with chronic heart failure even with altered trunk fixation.     

Muscle strength and weight-bearing symmetry relate to sit-to-stand performance in individuals with stroke

This study investigated the relationship of lower extremity joint torques and weight-bearing symmetry to sit-to-stand (STS) performance in individuals with chronic stroke. A motion analysis system and two force plates measured STS duration and weight-bearing symmetry (determined by ground reaction forces) during three self-paced and three fast-paced conditions. An isokinetic dynamometer measured maximum concentric joint torques of the paretic and non-paretic ankle, knee, and hip, which were normalized by body mass. Pearson correlations indicated that (a) paretic ankle dorsiflexion and knee extension torques related to the duration of the self-paced STS condition (r = -0.450, -0.716, respectively), (b) paretic ankle dorsiflexion, plantar flexion, and knee extension torques related to the duration of the fast-paced STS condition (r = -0.466, -0.616, -0.736, respectively), and (c) greater weight-bearing symmetry related to faster STS performance for both self-paced and fast-paced STS conditions (r = -0.565, -0.564, respectively) (P < 0.05). This evidence suggests that paretic muscle strength and the ability to load the paretic limb are important factors underlying the ability to rise from a chair in individuals with chronic stroke.     

Function of the quadriceps and hamstrings muscles in knees with chronic partial deficiency of the anterior cruciate ligament. Isometric and isokinetic evaluation.

We assessed the isokinetic and isometric strength and power profile of the knees of 37 patients who had a previous grade II sprain (partial tear) of the anterior cruciate ligament. Of the 37 knees, 11 had an isolated partial anterior cruciate ligament rupture and 26 had a partial anterior cruciate ligament rupture combined with a partial medial collateral ligament rupture. The Cybex II isokinetic dynamometer was used in the measurements. Eight years after the injury, the mean strength deficit of the injured knees was minimal when compared with the uninjured side. In the hamstrings of both groups, the relative strength deficit increased significantly with a higher speed of isokinetic movement (P less than 0.05). Compared with the strength parameters (peak torques), the other functional parameters (total work, average power, and peak angular impulse) of the injured knees showed some, but not significantly greater, deficits (hamstrings, 7% to 10%; quadriceps, 4% to 10%). We found that the general thigh muscle function in knees with old grade II sprains of the anterior cruciate ligament appears adequate except in flexion where the strength deficits are significantly greater in higher speeds of isokinetic movement. Therefore, rehabilitation using high-speed flexion (and extension) exercises is recommended.     

Proprioceptive neuromuscular facilitation training induced alterations in muscle fibre type and cross sectional area

Objectives: To compare the effects of proprioceptive neuromuscular facilitation (PNF) and isokinetic training on fibre type distribution and cross sectional area of the vastus lateralis muscle.

Methods: Twenty four male university students were divided into two equal groups: PNF training and isokinetic training (ISO). The training regimen for the PNF group consisted of three sets of 30 repetitions against maximal resistance, alternating two patterns of sequential movements of the right lower extremity: (a) toe flexion and ankle plantar flexion and eversion; (b) knee extension and hip extension, abduction, and internal rotation. The ISO group performed three sets of 30 repetitions alternating knee extension and flexion of the right leg at angular velocities of 180 and 90°/s in an isokinetic dynamometer (Cybex). Both groups trained three times a week for a total of eight weeks. Muscle biopsy specimens were obtained from the right vastus lateralis muscle before and after training.

Results: The mean percentage area of type IIB fibre was significantly decreased (p<0.01) after eight weeks of PNF training, whereas that of type IIA fibre was significantly (p<0.05) increased. The mean percentage area of ISO trained type IIAB fibres exhibited an augmentative pattern (p<0.01) with a parallel reduction (p<0.05) in type IIA. Percentage fibre type distribution exhibited a similar pattern.

Conclusions: Both PNF and ISO training alter fibre type distribution and mean cross sectional area. These changes occur in the type II fibre subgroup.

     

测试体位对髋关节功能运动等速测力结果的影响分析

本实验应用ｋｉｎ－Ｃｏｍ等速装置，通过对不同卧位、头的不同位置、关节不同功能位及手的摆放等形式以探讨测试体位的改变对等速力矩值的影响。３６名男性成年人参加了本实验，并随机分为２组，在６０°／ｓｅｃ角速度下进行了仰卧位、俯卧位髋伸；头正中位、同侧转动、对侧转动时髋屈、髋伸；髋屈９０°、膝屈９０°坐位、髋零位、膝屈９０°仰卧位髋内、外旋及手抓测试平台两侧、手不抓测试平台两侧时髋屈９０°、膝屈９０°坐位髋外旋。结果表明：俯卧位髋伸主要由于该体位时髋伸肌处于较佳的长度而使力矩值显著地大于仰卧位髋伸力矩值。头部的转动造成机体紧张性反射而使髋屈力量大小依次为头转向对侧、头正中位、头转向同侧，髋伸力量大小依次为头转向同侧、头正中位、头转向对侧，但相互之间无显著性差异存在。髋屈９０°、膝屈９０°坐位时，髋内、外旋力量均比髋零位、膝屈９０°仰卧位时要大，其中能内旋力量在两种体位下尚存有显著性差异，造成这一现象的主要原因为解剖方面的因素。手抓测试平台两边与否不致于产生髋外旋力量显著性的差异，其在稳定躯干、骨盆、大腿，使运动轴心相对恒定上有意义。离心收缩力量在测试体位改变时与向心收缩力量有相类似的表现。上述结果有益于等速测试和训?     

Knee flexor strength following anterior cruciate ligament reconstruction with the semitendinosus and gracilis tendons.

Knee flexor strength recovery following anterior cruciate ligament reconstruction with the doubled semitendinosus and gracilis tendons was assessed for up to 12 months post-surgery. Twelve patients were followed up, four at 3 months, five at 6 months and three at 12 months post-surgery. Knee flexor moment was recorded using the Biodex System-3 isokinetic dynamometer. Three sets of five repetitions of reciprocal eccentric/ concentric knee flexion contractions were carried out with each set at 1.05, 2.09 or 3.14 rad x s(-1). T-tests were used to test for significant differences between and within groups. The uninjured leg produced greater average peak moments than the injured leg; significant differences (p < 0.05) were seen between the legs at 1.05 rad x s(-1) for the 3-month group concentrically, and all three groups eccentrically. There was no significant difference (p > 0.05) between groups for the percentage deficit between legs. On average, a 23% deficit in average peak moment was still evident at 12 months both eccentrically and concentrically at 1.05 rad x s(-1). Taken as a whole this evidence suggests that there is a deficit in knee flexor strength up to at least 12 months post-surgery following doubled semitendinosus and gracilis tendon graft reconstruction even after a full rehabilitation protocol.     

Thigh muscle function after partial tear of the medial ligament compartment of the knee

The purpose of the study was to assess the isokinetic and isometric strength and power profile of the knees of 48 patients who had a previous second-degree sprain (partial tear) of the medial ligament compartment, the most common knee ligament injury in sports. The CYBEX II isokinetic dynamometer was used in the measurements. On an average of 8 yr after the injury, the mean strength deficit of the injured knees was minimal: 4 +/- 5% (range 0-28%) in extension and 2 +/- 4% (0-20%) in flexion. The average strength score (max. 100 points) was 90 +/- 11 (56-100), representing an excellent classification. In hamstrings, the relative strength deficit increased significantly with a higher speed of isokinetic movement (P less than 0.05). Compared with the strength parameters (peak torques), the other functional parameters of the injured knees (total work, average power, and peak torque acceleration energy) showed some but not significantly greater deficits (hamstrings 9-11%, quadriceps 6-8%). In conclusion, the general thigh muscle function in knees with old second-degree sprain of the medial ligament compartment appears good and acceptable, but the strength deficits are systematically greater in higher speeds of isokinetic movement. Therefore, rehabilitation utilizing high speed extension and flexion exercises is recommended.     

A biomechanical evaluation of tibiofemoral rotation in anterior cruciate deficient knees during walking and running

ACL injury has been associated with increased instability of the knee in both in vitro and in vivo studies using passively applied forces. This study assessed tibiofemoral rotation after ACL injury during the functional activity of treadmill ambulation using a triaxial electrogoniometer. Isometric and isokinetic peak torques of the quadriceps and hamstrings were obtained using the Cybex II isokinetic dynamometer. Significant increases in tibiofemoral rotation were noted with increased running speed in the injured and normal knees. The degree of rotation in the injured limb did not significantly exceed that of the normal limb. Isokinetic strength of the quadriceps and hamstrings correlates significantly with the observed extent of rotation.     

Isokinetic measurement in preadolescent males

Eighteen preadolescent males (mean age 11.4 +/- 0.59 years) performed 15 knee flexion-extension repetitions on both legs. Peak torque (T peak) and torque acceleration energy (TAE) were measured using the Cybex II Isokinetic system, which permitted a study of the effect of limb velocity on T peak, TAE, and reciprocal muscle group ratios. The effect of limb dominance was also assessed. The results indicated (Student's t test) that an increase in limb velocity from 1.05 rad/s to 4.2 rad/s produced a significant decrease in the T peak generated (P less than 0.001). A similar increase in limb velocity resulted in a significant increase in the TAE recorded (P less than 0.001). The limb velocity was also shown to influence the T peak and TAE ratios in reciprocal muscle groups. At a limb velocity 1.05 rad/s mean T peak ratios of 0.64 and 0.66 were recorded for the dominant and nondominant limbs, respectively. At 4.2 rad/s, ratios recorded for dominant and non-dominant limbs were 0.79 and 0.80, respectively. The limb velocity of 1.05 rad/s produced TAE ratios of 0.21 (dominant) and 0.14 (nondominant), and at 4.2 rad/s, ratios of 0.28 and 0.24 were recorded for dominant and non-dominant limbs, respectively. No significant difference (P less than 0.001) was observed between T peak and TAE values recorded for the dominant and non-dominant limbs under the same conditions. These results indicate that young boys show velocity-related isokinetic strength characteristics similar to adults. Although they have lower absolute levels, the children showed typical adult reciprocal muscle group ratios. Limb dominance at this age is not reflected in strength differences.     

Caffeine ingestion and isokinetic strength.

The purpose of this study was to investigate the effects of caffeine on maximum voluntary contractions of the dominant knee extension and flexion muscles in 12 male intercollegiate track sprinters. Caffeine (5 mg.kg-1) and placebo (225 mg methylcellulose) gelatin capsules were administered orally in randomly assigned order. Muscle function was measured isokinetically by a Cybex II dynamometer interfaced with a data reduction computer. Six repetitions maximum of the extensors and flexors were performed at three sequential ordered speeds (30 degrees, 150 degrees and 300 degrees s-1) with a one-minute rest between varying velocities. Peake torque and power were than assessed after treatment conditions, as well as a fatigue index calculated from a series of 60 repetitions maximum ato 150 degrees s-1. Results of the 2 X 3 ANOVA and paired t-test indicated no difference in measures of peak torque and power at the varying contracting velocities and fatigue index after caffeine ingestion. These findings indicate the ingestion of caffeine in a small dose exerts no ergogenic effect on muscle function under anaerobic conditions.     

Effect of activation force on knee extensor torques

The purpose of this study was to determine whether the magnitude of the activation force, defined as the force that must be applied to the load cell in order to activate the resistance arm of an isokinetic dynamometer, affected knee extensor torques. Twenty-four healthy female subjects performed resisted knee extension through the range of 95 degrees to 5 degrees knee flexion, with a 5-s rest between concentric and eccentric muscle actions. Six exercise sets, composed of the combinations of activation force (20,50, and 100 N) and angular velocity (45 and 135 degrees.s-1), were randomly assigned on each of two occasions, completed within a 10-d period. Although peak torques were not affected by the activation force, average torques, eccentric torques at mid-range (50 degrees knee flexion), and torques during the initial portion of each muscle action (80 degrees knee flexion during concentric muscle actions and 20 degrees flexion during eccentric actions) increased as the activation force increased. The effect of the activation force tended to be more pronounced during eccentric than during concentric muscle actions, and at the faster angular velocity. Comparisons of torques should be based on similar test protocols, including activation force.     

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.     

Subject variability of shoulder abduction strength testing

To quantify normal biological variability of shoulder abduction strength testing with an isokinetic and a hand-held dynamometer, we tested nine healthy subjects over a clinically relevant period. One side was tested with a Cybex at 60 deg/sec and the other with a hand-held dynamometer. Six maximal trials, following warmup, were conducted on each of 5 days, separated by 1 to 2 weeks. Intraday correlations of individual trials ranged from 0.82 to 0.995 for hand-held dynamometer, and 0.88 to 0.996 for Cybex. Interday correlations ranged from 0.94 to 0.98 for hand-held dynamometer, and 0.88 to 0.97 for Cybex. The best values to use for Cybex interday variability were the average of the first three repetitions, and yielded standard errors of 8.6% to 19.2% of the sample mean. The average of the last three repetitions were the best for hand-held dynamometers, and yielded standard errors of 5.5% to 10.8%. There was a significant decline (P less than 0.05) in strength of the mean of the last three versus the mean of the first three daily repetitions on Day 1 and 4 for hand-held dynamometers, and a trend toward this on the other days, that was not seen with Cybex. Regression of average Day 1 values for Cybex and hand-held dynamometer yielded r = 0.86 (P less than 0.01) with a slope of 1.07 indicating good agreement between modalities. In conclusion, intraday/interday correlations were high for Cybex and hand-held dynamometer. Interday variability was minimized by using the mean score of the first three and last three repetitions for Cybex and hand-held dynamometer, respectively. Changes in Cybex and hand-held dynamometer strength of less than 19% and 11%, respectively, are within the area of "measurement error" and should therefore not be considered clinically significant.     

Isolated hip and ankle fatigue are unlikely risk factors for anterior cruciate ligament injury

Lower extremity neuromuscular fatigue purportedly increases anterior cruciate ligament (ACL) injury risk through promotion of extreme landing mechanics. However, the impact of fatigue on muscle groups critical to the landing strategy remains unclear. This study examined the effects of isolated hip rotator and triceps surae fatigue on lower extremity landing biomechanics. Sixteen healthy females (18–22 years) reported for testing on two occasions, with one muscle group fatigued per session. Subjects performed three single‐leg landings onto a force platform pre‐ and post‐fatigue, defined as an 80% decrease in peak torque in the targeted muscle group. Hip rotator fatigue was induced via alternating concentric contractions and triceps surae fatigue through concentric plantar flexion contractions on an isokinetic dynamometer. Initial contact (IC) kinematics and peak stance (PS) kinetics and kinematics were analyzed pre‐ and post‐fatigue. Hip rotator fatigue increased IC (P=0.05) and PS (P=0.04) hip internal rotation angles. Triceps surae fatigue decreased IC knee flexion (P=0.01) angle. Isolated hip rotator and triceps surae fatigue each produced modifications in lower limb kinematic parameters viewed as risk factors for ACL injury. These modifications, however, do not appear of sufficient magnitude to compromise ligament integrity, suggesting injury via an integrative lower extremity fatigue mechanism is more likely.     

Isokinetic strength of the quadriceps and hamstrings and functional ability of anterior cruciate deficient knees in recreational athletes.

OBJECTIVE: To test the hypothesis that increasing the hamstrings and quadriceps (H:Q) isokinetic strength ratio will, in the short term, improve the functional ability of an anterior cruciate ligament (ACL) deficient knee. METHODS: The isokinetic muscular characteristics at a speed of 60 degrees s-1 and 180 degrees s-1 of 46 recreational athletes with an arthroscopically confirmed ACL tear were determined using the Cybex II+ isokinetic dynamometer. The variables tested included peak torque, endurance ratio, total work output, and explosive power. Functional ability was scored with the Cincinnati rating system, measuring the severity of pain and swelling, the degree of giving way, and the overall ability to walk, run, ascent and descent stairs, jump and twist. RESULTS: Among all muscular characteristics, the H:Q ratio at 180 degrees s-1 at 30 degrees of knee flexion was shown to have the highest correlation to the functional score (r = 0.6249, P < 0.001). All variables involving hamstring strength were shown to be significantly correlated to the functional ability score (P < 0.01), while none of the variables involving quadriceps strength showed significant correlation with the functional ability of the injured knee. CONCLUSIONS: The H:Q ratio is strongly correlated to the functional ability of ACL deficient knees in Chinese recreational athletes. It could be used as an additional measure to guide in the decision making process in the management of ACL deficient knees.     

Effect of high velocity resistance training on peak torque, cross sectional area and myofibrillar ATPase activity.

The purpose of this investigation was to determine the effect of high velocity resistance (HVR) training on peak torque (PT), cross sectional area (CSA) and myofibrillar ATPase activity of the knee extensors. HVR training was performed in a circuit on hydraulic exercise equipment, 4 times a week for 5 weeks at an angular velocity of approximately 3.14 rad.s-1. Knee extension PT was determined on a Cybex II isokinetic dynamometer and CSA of the quadriceps femoris muscle was assessed using computer tomography (CT) scanning. Muscle biopsies were obtained from the lateral quadriceps muscle and were analyzed for myofibrillar ATPase activity. Knee extension peak torque was significantly increased at 1.57, 2.09, 3.14, 3.66 and 4.19 rad.s-1. Myofibrillar ATPase activity and CSA was also significantly increased after HVR training. These findings showed that short-term high velocity resistance training enhances the in vivo torque/velocity curve especially at fast angular velocities and these changes are partly attributed to an increase in muscle CSA and activity of myofibrillar ATPase.     

The relationship between isokinetic knee extension and flexion strength with soccer kick kinematics: an electromyographic evaluation

AIM: The purpose of this study was to investigate the relationship between isokinetic strength knee testing and soccer kick kinematics using electromyography (EMG). METHODS: Thirteen pubertal soccer players (age: 14.3+/-0.4 years) performed maximum instep soccer kicks, while knee angular position of the swinging leg was recorded using a twin-axis electrogoniometer. Bipolar surface EMG activity of the vastus medialis, vastus lateralis and biceps femoris (BF) muscles was recorded. The subjects also performed maximum knee extension and flexion efforts at concentric angular velocities of 1.04, 3.14 and 5.23 rad x s(-1) and eccentric angular velocities of 1.04 and 3.14 rad x s(-1). RESULTS: The correlation coefficients between isokinetic moments and knee angular velocity values during the kick ranged from 0.609 to 0.898 for concentric moments and from 0.431 to 0.612 for eccentric moments. Agonist EMG values during isokinetic tests ranged from 63.17+/-19.9% to 128.7+/-34.9% maximum voluntary contraction (MVC). Antagonist EMG levels ranged from 9.76+/-6.12% to 36.91+/-22.81% MVC. The corresponding EMG values during the soccer kick ranged from 12.78+/-6.8% to 122.34+/-61.5% MVC and increased as the foot approached the ball. CONCLUSION: Isokinetic tests at intermediate and fast angular velocities are adequate for monitoring strength training programs in soccer. However, muscle activation patterns differ between the two movements, especially those of the BF muscle.     

Seasonal deterioration of selected physiological variables in elite male skiers.

The purpose of this study was to determine whether seasonal deterioration in physiological variables could be observed in skiers. Eighteen international male British downhill, free-style, and speed skiers were subjected to a maximal treadmill running test, a 30-s Wingate test, and isokinetic dynamometry at the beginning, middle, and end of the 1989-90 competition season. Maximal oxygen intake (VO2max) and respiratory anaerobic threshold (T vent) were among the parameters measured on the treadmill test, while peak and mean power outputs were measured during the Wingate test. During dynamometry, knee flexors and extensors were bilaterally assessed at 1.04 and 3.14 rad.s-1. Mean VO2max (p < 0.01) and mean T vent (p < 0.05) were lower at the end compared to the beginning, but not compared to the middle of the competition season. The isokinetic test demonstrated lower mean peak torques at 1.04 rad.s-1, for the knee extensors measured at the end of the season, compared with both the start (p < 0.01) and the middle (p < 0.05). Also at 1.04 rad.s-1, knee flexors produced lower torques at the end than the start of the season (p < 0.05). No further statistical differences were found. It was concluded that seasonal deterioration in key physiological variables such as aerobic endurance and muscle strength, can be observed in elite alpine skiers, and that in-season fitness training programmes should take account of this.     

Knee strength variability between individuals across ranges of motion and hip angles

PURPOSE: Isokinetic strength is normally measured for a single range of motion and body position. This study quantified the variability, between individuals, in the relationships between a single peak knee extension moment and the isokinetic extension moments measured for different hip angles and ranges of knee motion. Effects of hip angle, and of the starting knee angle of the range of motion, on isokinetic knee extension strength were also determined. METHODS: The isokinetic knee extension strength of 10 subjects was measured at 30 degrees x s(-1) to a knee flexion angle of 10 degrees from starting knee angles of 90, 75, 60, 45, and 30 degrees, in both the seated and supine positions. Moments were normalized to the peak moment from a reference contraction. RESULTS: Peak moments and moments at larger knee flexion angles were greater in the seated than in the supine position. The starting knee angle affected the peak moment, the angle of peak moment, and the moments over the initial and final portions of the range of motion. Peak moments were highly correlated between all hip angle-starting knee angle combinations. However, the normalized peak moments, the angles of peak moment, and the normalized angle-specific moments all varied considerably between subjects. The pooled standard deviation and average coefficient of variation of the normalized angle-specific moments between subjects were 10.5% of the normalizing moment and 15.7%, respectively. Excluding the reference contraction, between-subject variability was unaffected by hip angle or starting knee angle. CONCLUSIONS: Influences of hip angle, starting knee angle, and individual differences on isokinetic knee extension strength must be considered to ensure that the moments obtained from isokinetic testing adequately reflect the general strength capabilities of an individual.     

Calf muscle strength in humans

In an effort to measure strength characteristics of the calf muscles, 18 subjects (14 male, 4 female, age =34.3+/-2.4yrs) were tested using a specially designed torque velocity device (TVD). This TVD is a hardware interface with the subject's lower leg which stabilizes the leg for calf muscle strength measurements. Calf muscle strength measurements consisted of 1) isometric force production at ankle angles of 80, 90, and 100 degrees of plantar flexion, 2) peak torque at six isokinetic angular velocities 0.52, 1.05, 2.09, 3.14, 4.19, and 5.24 rad x s(-1), and 3) a fatigue test consisting of 30 maximal contractions at 3.14 rad x s(-1). The greatest force production occurred at 80 degrees of ankle plantar flexion (148.5 +/- 40.2 Nm). Isokinetic force production ranged from 114.1 +/- 24.7 Nm at 0.52 rad x s(-1) to 16.8 +/- 6.5 Nm at 5.24 rad x s(-1). A fatigue test consisting of 30 maximal repetitions at 3.14 rad x s(-1) resulted in a 61 +/- 15% decline in force production. To assess reproducibility and day to day variation, measurements at 1.05 and 2.09 rad x s(-1) were made during five different trials in a single day and one trial per day for three days, respectively. The within subject coefficient of variation was 2.6 to 6.5% for reproducibility and 1.9 to 7.4% for day to day variation. Magnetic resonance imaging (MRI) of the lower limb and muscle biopsy specimens from the gastrocnemius (lateral head) and soleus muscles were obtained to examine the relationship between strength and morphological characteristics of the calf muscles. Cross-sectional area of the primary plantar flexors (gastrocnemius and soleus) was 47.9 +/- 1.3 cm2 while muscle volume was 642 +/- 16 cm3. Muscle fiber composition of the gastrocnemius and soleus averaged 57 +/- 2 and 85 +/- 3% type I fibers, respectively. A poor correlation was found between fiber type and maximal isometric force production (r =0.38; p>0.05). However, calf muscle strength and muscle size was positively correlated (r = 0.76; p < 0.05). These data indicate that using the TVD interface to stabilize the lower leg is a reliable and reproducible procedure for the measurement of calf muscle strength.