MUSCLE ACTIVATION AND THE ISOKINETIC TORQUE-VELOCITY RELATIONSHIP OF THE HUMAN TRICEPS SURAE

The influence of muscle activation and the time allowed for torque gen eration on the angle-specific torque-velocity relationship of the tric eps surae was studied during plantar flexion using supramaximal electr ical stimulation and a release technique on six male subjects [mean (S D) age 25 (4) years]. Torque-velocity data were obtained under differe nt levels of constant muscle activation by varying the stimulus freque ncy and the time allowed for isometric torque generation prior to rele ase and isokinetic shortening. To eliminate the effects of the frequen cy response on absolute torque the isokinetic data were normalized to the maximum isometric torque values at 0.44 rad. There were no signifi cant differences in the normalized torques generated at any angular ve locity using stimulus frequencies of 20, 50 or 80 Hz. When the muscle was stimulated at 50 Hz the torques obtained after a 400 ms and t s pr e-release isometric contraction did not differ significantly. However, with no pre-release contraction significantly less torque was generat ed at all angular velocities beyond 1.05 rad.s-1 when compared with ei ther the 200, 400 ms or 1 s condition. With a 200 ms pre-release contr action significantly less torque was generated at angular velocities b eyond 1.05 rad.s-1 when compared with the 400 ms or 1 s conditions. It would seem that the major factor governing the shape of the torque-ve locity curve at a constant level of muscle activation is the time allo wed for torque generation.