FORCE RESPONSES TO CONTROLLED STRETCHES OF ELECTRICALLY STIMULATED HUMAN MUSCLE-TENDON COMPLEX

Human first dorsal interosseus muscle was tetanized using percutaneous electrical stimulation. During the tetanus the muscle was subjected t o constant velocity stretches, The stretch produced an enhancement of muscular force of up to 80% during the stretch. The size of the enhanc ement was dependent on both the amplitude and the velocity of the stre tch. During an isometric hold phase after the stretch, the force decay ed quickly for the first 100 ms and thereafter much more slowly, reach ing a level 30% higher than the isometric force without pre-stretch. T he force during this hold phase was dependent on amplitude of stretch but was independent of stretch velocity. The interaction of tendon ela sticity and muscle fibre mechanics in producing these responses is dis cussed. Implications for normal human movements are also explored.