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Publication

Force depression and relaxation kinetics after active shortening and deactivation in mouse soleus muscle

Journal Contribution - Journal Article

After active shortening, isometric force production capacity of muscle is reduced (force depression, FD). The mechanism is incompletely understood but increasing cross-bridge detachment and/or decreasing attachment rate might be involved. Therefore we aimed to investigate the relation between work delivered during shortening (W), and change in half-relaxation time (Delta 0.5RT) and change in the slow phase of muscle relaxation (Delta k(slow)), considered as a marker for cross-bridge detachment rate, after shortening and after a short (0.7 s) interruption of activation (deactivation). We hypothesized that shortening induces an accelerated relaxation related to W which is, similar to FD, largely abolished by a short deactivation. In 10 incubated supra-maximally stimulated mouse soleus muscles, we varied the amount of FD at L-0 by varying shortening amplitude (0.6, 1.2 and 2.4 mm). We found that W not only induces FD (R-2=0.92) but also a dose dependent accelerated relaxation (R-2=0.88 and R-2=0.77 for respectively Delta k(slow), and Delta 0.5RT). In cyclic movements this is of functional significance, because the loss in force generating capacity might be (partially) compensated by faster relaxation. After a short deactivation, both FD and Delta k(slow) were largely abolished but Delta 0.5RT remained largely present. Under the assumption that Delta k(slow), reflects a change in cross-bridge detachment rate, these results support the idea that FD is an intrinsic sarcomeric property originating from a work induced reduction of the number of force generating cross-bridges, however not via decreased attachment but via increased detachment rate. (
Journal: J Biomech
ISSN: 0021-9290
Issue: 5
Volume: 46
Pages: 1021-1026
Publication year:2013
Keywords:Force Depression
  • Scopus Id: 84875257935