Abstract
Muscle force generated during shortening is instantaneously increased after active stretch. This phenomenon is called as stretch-shortening cycle (SSC) effect. It has been suggested that residual force enhancement contributes to the SSC effect. If so, the magnitude of SSC effect should be larger in the longer muscle length condition, because the residual force enhancement is prominent in the long muscle length condition. This hypothesis was examined by performing the SSC in the short and long muscle length conditions. Skinned fibers obtained from rabbit soleus (N = 20) were used in this study. To calculate the magnitude of SSC effect, the SSC trial (isometric-eccentric-concentric-isometric) and the control trial (isometric-concentric-isometric) were conducted in the short (within the range of 2.4 to 2.7 μm) and long muscle (within the range of 3.0 to 3.3 μm). The magnitude of SSC effect was calculated as the relative increase in the mechanical work attained during the shortening phase between control and SSC trials. As a result, the magnitude of SSC effect was significantly larger in the long (176.8 ± 18.1%) than in the short muscle length condition (157.4 ± 8.5%) (p < 0.001). This result supports our hypothesis that the magnitude of SSC effect is larger in the longer muscle length condition, possibly due to the larger magnitude of residual force enhancement.
Highlights
Muscle force generated during shortening is instantaneously increased after active stretch
Because the stretch-shortening cycle (SSC) effect was confirmed in single skinned muscle fiber preparations which do not include the influence of neural activation and tendon elongation[7], it is highly likely that other factors contribute to the SSC effect
This is in line with the results that the magnitude of residual force enhancement (RFE) is prominent in the descending limb of the force-length relationship[14,15,16], the cross bridge interactions are less in the descending limb than in the plateau region
Summary
Muscle force generated during shortening is instantaneously increased after active stretch. The magnitude of SSC effect should be larger in the longer muscle length condition, because the residual force enhancement is prominent in the long muscle length condition. This is in line with the results that the magnitude of RFE is prominent in the descending limb of the force-length relationship[14,15,16], the cross bridge interactions are less in the descending limb than in the plateau region Taking this into account, it is hypothesized that the magnitude of SSC effect is larger in the descending limb because the magnitude of RFE, one of the possible mechanisms of the SSC effect, is larger in the descending limb. We hypothesized that the magnitude of SSC effect is larger in the long muscle length condition due to the larger RFE in the long muscle length condition[14,15,16]
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