The increase or decrease in isometric force following active muscle lengthening or shortening, relative to a reference isometric contraction at the same muscle length and level of activation, are referred to as residual force enhancement (rFE) and residual force depression (rFD), respectively. The purpose of these experiments was to investigate the trainability of rFE and rFD on the basis of serial sarcomere number (SSN) alterations to history-dependent force properties. Maximal rFE/rFD measures from the soleus and extensor digitorum longus (EDL) of rats were compared after 4 weeks of uphill or downhill running with a no-running control. SSN adapted to the training: soleus SSN was greater with downhill compared with uphill running, while EDL demonstrated a trend towards more SSN for downhill compared with no running. In contrast, rFE and rFD did not differ across training groups for either muscle. As such, it appears that training-induced SSN adaptations do not modify rFE or rFD at the whole-muscle level.
50The increase or decrease in isometric force following active muscle lengthening or shortening, 51 relative to a reference isometric contraction at the same muscle length and level of activation, are 52 referred to as residual force enhancement (rFE) and residual force depression (rFD), respectively. 53The purpose of these experiments was to gain further mechanistic insight into the trainability of 54 rFE and rFD, on the basis of serial sarcomere number (SSN) alterations to length-dependent 55properties. Maximal rFE/rFD measures from the soleus and extensor digitorum longus (EDL) of 56 rats were compared after 4 weeks of uphill/downhill running and a no running control. Serial 57 sarcomere numbers adapted to the training: soleus serial sarcomere number was greater with 58 downhill compared to uphill running, while EDL demonstrated a trend towards more serial 59 sarcomeres for downhill compared to no running. In contrast, absolute and normalized rFE/rFD 60 did not differ across training groups for either muscle. As such, it appears that training-induced 61 SSN adaptations do not modify rFE/rFD at the whole-muscle level. 62 63 65
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