Depression of cat soleus-forces following isokinetic shortening.

The purpose of this study was to test the hypothesis that force depression following muscle shortening is caused by stress-induced inhibition of the cross-bridges in the zone of new overlap between thick and thin filaments. Force depressions following shortening were assessed in five separate tests on the cat soleus. It was found that force depressions following shortening were inversely related to the speed of shortening and were directly related to the amount of shortening, which is in agreement with published results on muscles and fibre preparations. It was further observed that the force depressions were directly related to the force produced during the shortening phase, and that the force depressions were systematically reduced by relaxing the stress on the muscle following shortening. These latter results could not be compared with corresponding literature values for lack of systematic testing of these properties in mammalian skeletal muscle. All results of this study supported the predictions which were made based on our working hypothesis proposed above. The results also confirmed that there are long-lasting, time-dependent properties of skeletal muscle which are not part of the cross-bridge theory of muscular force production and which are ignored in Hill-type models of skeletal muscle.