Influence of fiber type on stretch shortening cycle and residual force enhancement

Recently, we suggested that cross-bridge kinetics and residual force enhancement (RFE) contribute to the stretch-shortening cycle (SSC) effect. Cross-bridge kinetics and RFE are affected by fiber type. Therefore, we examined the influence of fiber type on the SSC effect and RFE. Rabbit psoas and soleus were used as representatives of a fast and a slow twitch-fibred muscle, respectively. We performed pure shortening (control test) and shortening following eccentric contraction (SSC test) experiments to observe the SSC effect. We also performed pure isometric contractions (control test) and isometric contractions following eccentric contraction to quantify RFE independently. The magnitude of the SSC effect was greater in the soleus than the psoas muscle, while RFE was the same in both muscles. These results suggest that the difference in the SSC effect between soleus and psoas was not caused by RFE, but by the cross-bridge kinetics.