The development of active isokinetic dynamometers has allowed the assessment of muscular moment under eccentric activations that have different characteristics to concentric actions. It is well documented that at a given angular velocity the eccentric moment is greater than the corresponding concentric moment. The moment-velocity relationship under eccentric conditions has been investigated, with conflicting results. Particularly, eccentric moment was reported to remain similar to, or to increase or decrease with, increasing angular velocity. As with concentric actions, the reliability of isokinetic eccentric measurements is influenced by a number of factors such as gravity, preload force and testing position.

Isokinetic eccentric exercise.

OBJECTIVE: The use of muscle balancing by the clinician to determine return to activity or discharge of a patient is not a well understood measure. Because of the lack of information on the poorly understood concept of eccentric/concentric (E/C) ratios at the ankle, the purpose was to determine the E/C ratios for the invertor and evertor muscles at various velocities in healthy and chronically unstable ankles. METHODS: Ten subjects with healthy ankles and 14 with chronically unstable ankles performed five maximal effort reciprocal eccentric/contraction contractions on an isokinetic dynamometer at four velocities (60, 120, 180, and 240 degrees/s) and for each physiological movement of inversion and eversion. Data were analysed using a two way mixed model analysis of variance with repeated measures, with Tukey's test used for post hoc analysis. RESULTS: Although the chronically unstable ankle was significantly weaker (p < 0.05) eccentrically and concentrically for inversion and eversion, the main effect of the E/C ratios for the ankle was not significant for either joint motion. The main effect of velocity was significant (p < 0.05) for each joint motion, but no significant interaction effects were observed. As velocity increased, the E/C ratio increased, except at 180 and 240 degrees/s for either ankle group. CONCLUSIONS: Chronic ankle instability and muscle weakness co-exist. Adequate E/C ratios in the chronically unstable ankle may exist in the absence of normal strength values.

https://bjsm.bmj.com/content/bjsports/33/4/255.full.pdf

Eccentric/concentric ratios at selected velocities for the invertor and evertor muscles of the chronically unstable ankle.

Series cross-section images of the upper extremity were obtained for four men by magnetic resonance imaging (MRI) and anatomical cross-sectional areas (ACSA) of elbow flexor muscles [biceps brachii (BIC), brachialis (BRA), brachioradialis (BRD)] and extensor muscles [triceps brachii (TRI)] were measured Physiological cross-sectional area (PCSA) was calculated from the muscle volume and muscle fibre length, the former from the series ACSA and the latter from the muscle length multiplied by previously reported fibre/muscle length ratios Elbow flexion/extension torque was measured using an isokinetic dynamometer and the force at the tendons was calculated from the torque and moment arms of muscles measured by MRI Maximal ACSA of TRI was comparable to that of total flexors, while PCSA of TRI was greater by 19 times Within flexors, BRA had the greatest contribution to torque (47%), followed by BIC (34%) and BRD (19%) Specific tension related to the estimated velocity of muscle fibres were similar for elbow flexors and extensors, suggesting that the capacity of tension development is analogous between two muscle groups

Specific tension of elbow flexor and extensor muscles based on magnetic resonance imaging

OBJECTIVE: To determine the reliability of the Cybex 6000 isokinetic dynamometer in measuring the knee muscle performance concentrically and eccentrically. METHODS: 18 male and 12 female subjects with no previous knee injuries, who had not previously undergone any isokinetic testing, were studied. The flexor and extensor muscles groups of both knees were tested at 60 degrees s-1 and 120 degrees s-1 with the continuous concentric-eccentric cycle testing protocol. Variables studied included peak torque, total work, and average power. The interclass correlation coefficient (ICC 2,1) was used to determine the reliability with P < 0.05. RESULTS: Peak torque showed significantly greater ICC than the total work and average power, with test-retest reliability ranging from 0.82 to 0.91 for peak torque, from 0.76 to 0.89 for total work, and 0.71 to 0.88 for average power. Average variability for the three variables studied ranged from 9% to 14%. The ICCs for the three variables studied were significantly greater at 120 degrees s-1. The knee extensor muscle group showed greater test-retest reliability, and the results of isokinetic testing in the concentric contraction mode were more reproducible. CONCLUSIONS: The Cybex 6000 isokinetic dynamometer shows high reliability in measuring isokinetic concentric and eccentric variables. Some fluctuation should be allowed when evaluating variations of muscle performance between tests.

https://bjsm.bmj.com/content/bjsports/30/2/156.full.pdf

Eccentric and concentric isokinetic knee flexion and extension: a reliability study using the Cybex 6000 dynamometer.

Background and Purpose. Although surgical reconstruction of the anterior cruciate ligament (ACL) is commonly performed to increase stability of the knee, persistent changes in neuromuscular function have frequently been cited as contributing to disability. This study investigated single-leg standing balance in a sample of patients 10 to 18 months following reconstructive ACL surgery. In addition, the effect of leg dominance on standing balance was analyzed in a sample of subjects without knee injury. The validity and interrater reliability of a clinical method of measuring balance using observation were also determined. Subjects. Seventy-eight subjects without knee injury and 17 patients following ACL surgery participated in the study after they had been screened for balance disorders. Methods. Postural sway measurements were recorded during single-leg standing with the subjects' eyes open and closed. Simultaneously, two physical therapists graded each subject's performance using a simple ordinal scale. Results. No differences were found between the dominant and nondominant legs of the subjects without knee injury or between the involved and noninvolved legs of the patients who had undergone ACL surgery. The interrater reliability was high, but limited concurrent validity was found. Conclusion and Discussion. The findings suggest that single-leg standing balance can be reliably evaluated by physical therapists. The single-leg standing balance test, however, may not provide information that assists clinicians in determining clinical change or functional level for patients following rehabilitation for ACL surgery.

Evaluation of Single-Leg Standing Following Anterior Cruciate Ligament Surgery and Rehabilitation

The purpose of this study was to compare differences in eccentric and concentric peak torque and power measurements of knee extensors at different velocities. The subjects included 21 females between the ages of 19 and 28, who had no history of knee pain or abnormality. Eccentric and concentric contractions of the knee extensors of the dominant leg of each subject were tested on an isokinetic dynameter at 60 degrees/s, 120 degrees/s and 180 degrees/s. Eccentric peak torque was greater than concentric at each of the three velocities tested, whereas eccentric power was significantly greater only at the two higher velocities. The lack of change in concentric peak torque between 120 degrees/s and 180 degrees/s contrasted with results of other studies, probably owing to methodological differences. Eccentric torque increased from 60 degrees/s to 120 degrees/s, but decreased again at the highest velocity. Both concentric and eccentric power increased with velocity.

M Rizzardo

Papers

Eccentric and concentric torque and power of the knee extensors of females.