Contribution of passive resistive torque to total peak concentric isokinetic torque of the calf muscle-tendon unit

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The purpose of this study was to examine the contribution of the passive resistive torque to the total peak concentric isokinetic torque of the calf muscle-tendon unit. Thirty healthy, active women (age: 32 [SD 8] years) were tested using a KIN-COM 500H force dynamometer. The right calf muscle-tendon unit was first stretched passively at 5°.s -1 from relaxed plantar flexion to the maximal angle of available dorsiflexion to measure the passive resistive torque. Subjects then performed maximal concentric plantar flexion from the maximal dorsiflexion angle at randomized test velocities of 30, 60, 120 and 180°.s -1 . The passive resistive torque was subtracted from the total concentric peak torque to determine the active concentric peak torque. The angular delay from the onset of movement to the angle of total peak and active peak torques, and the percent contribution of the passive resistive torque to the total peak torque were calculated. One-way ANOVA procedures showed that the total and active peak torques decreased, and their respective angular delays increased, with increasing test velocities (P < 0.001). The active peak torque was less than the total peak torque (P < 0.001), and the angular delay for the active peak torque was greater than for the total peak torque among all test velocities (P < 0.001). The percent contribution of the passive resistive torque to the total peak torque ranged from 10.5% to 11.5%, but this did not differ among the four concentric test velocities. The passive resistive torque contributed significantly to the total peak concentric torque and shifted the angular delay toward the onset of movement. The passive resistive torque contribution was essentially constant among the four test velocities, probably influenced by the decrease in concentric peak torques and the increase in the angular delay that resulted from the increasing test velocities.