FORCE RESPONSES TO CONSTANT-VELOCITY SHORTENING OF ELECTRICALLY STIMULATED HUMAN MUSCLE-TENDON COMPLEX

Cook, C. S., and M. J. N. McDonagh. Force responses to constant-veloci ty shortening of electrically stimulated human muscle-tendon complex. J. Appl. Physiol. 81(1): 384-392, 1996.-Force-velocity curves in human muscle often have unexpectedly high forces at high velocities. If ser ies elasticity is the cause, it should have less effect at lower activ ation levels and larger shortening amplitudes. The first dorsal intero sseus muscle-tendon complex was shortened at different levels of activ ation and by different amplitudes. Force-velocity curves had high forc e well maintained at high velocities. With an actuator release of 4.21 mm at 80% of maximal activation, force was > 45% of isometric force ( P-0) for all actuator velocities > 200 mm/s (1.49 muscle lengths/s). A t 30% activation, the force was > 25% of P-0 at these velocities. The smaller 2.46-mm releases produced higher forces than the 4.21-mm relea ses at these velocities. At 80% activation, force was > 65% of P-0, an d at 30% activation, it was > 50% of P-0 at these velocities. Correcti ons of these data for elasticity produced classic Hill-type force-velo city curves. A model incorporating the Hill force-velocity equation an d a spring in series accounts for the results.