The stretch-shortening cycle effect is prominent in the inhibited force state

Abstract

It has been suggested that residual force enhancement (RFE) contributes to the work enhancement observed in stretch-shortening cycles (SSC). Based on recent findings that RFE was preserved in the reduced force state, one may speculate that the SSC effect may be preserved in the reduced force state as well. The purpose of this study was to examine the magnitude of the SSC effect in inhibited skeletal muscle force states. Normal and inhibited force conditions were analyzed using skinned rabbit soleus fibres (N = 18). The inhibited force condition was achieved by adding 2,3-Butanedione monoxime into the activating solution. For both conditions, a SSC test and a pure shortening test were performed. In the SSC tests, fibres were activated at an average sarcomere length of 2.4 μm, and then stretched to 3.0 μm. Immediately after the end of the stretch, fibres were shortened to 2.4 μm. In the pure shortening tests, fibres were activated at an average sarcomere length of 3.0 μm and then shortened to 2.4 μm. The relative increase in mechanical work in the shortening phase of the SSC compared to the pure shortening condition was defined as the SSC effect index, and the magnitude of the SSC effect was compared between the normal and the inhibited force condition. The SSC effect was greater in the inhibited compared to the normal force condition (p < 0.001). We conclude that the SSC effect is at least in part preserved in the reduced force state.