Modifiability of residual force depression in single muscle fibres following uphill and downhill training in rats

Mashouri, Parastoo
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University of Guelph

Following active muscle shortening, steady-state isometric force is less than a purely isometric contraction at the same muscle length and level of activation; this is known as residual force depression (rFD). The purpose of this thesis was to investigate whether rFD in single muscle fibres is modifiable through downhill and uphill running in the extensor digitorum longus (EDL) and soleus (SOL) muscles in rats. Rats were randomly assigned to either a control or intervention group, where they were run uphill or downhill 5 days/wk for 4 wks. rFD was present for both the EDL (6-15%) and SOL (1-2%), with no effect of training. rFD was greater for the EDL than SOL which closely corresponded to the greater work of shortening and stiffness depression in the EDL. These results indicate that while rFD was observed, training did not appear to alter this intrinsic history-dependent property of single muscle fibres.

force depression, rFD, single muscle fibres, work of shortening