Passive muscle stretching reduces estimates of persistent inward current strength in soleus motor units

Document Type

Journal Article

Publication Title

Journal of Experimental Biology

Volume

223

Issue

21

Publisher

The Company of Biologists Ltd

School

Centre for Exercise and Sports Science Research / School of Medical and Health Sciences

RAS ID

32427

Comments

Trajano, G. S., Taylor, J. L., Orssatto, L. B. R., McNulty, C. R., & Blazevich, A. J. (2020). Passive muscle stretching reduces estimates of persistent inward current strength in soleus motor units. Journal of Experimental Biology, 223(21), article jeb229922. https://doi.org/10.1242/jeb.229922

Abstract

© 2020. Published by The Company of Biologists Ltd. Prolonged ( ≥ 60 s) passive muscle stretching acutely reduces maximal force production at least partly through a suppression of efferent neural drive. The origin of this neural suppression has not been determined; however, some evidence suggests that reductions in the amplitude of persistent inward currents (PICs) in the motoneurons may be important. The aim of the present study was to determine whether acute passive (static) muscle stretching affects PIC strength in gastrocnemius medialis (GM) and soleus (SOL) motor units. We calculated the difference in instantaneous discharge rates at recruitment and de-recruitment (ΔF) for pairs of motor units in GM and SOL during triangular isometric plantar flexor contractions (20% maximum) both before and immediately after a 5 min control period and immediately after five 1 min passive plantar flexor stretches. After stretching, there was a significant reduction in SOL ΔF (-25.6%; 95% confidence interval, CI=-45.1% to -9.1%, P=0.002) but not GM ΔF These data suggest passive muscle stretching can reduce the intrinsic excitability, via PICs, of SOL motor units. These findings (1) suggest that PIC strength might be reduced after passive stretching, (2) are consistent with previously established post-stretch decreases in SOL but not GM EMG amplitude during contraction, and (3) indicate that reductions in PIC strength could underpin the stretch-induced force loss.

DOI

10.1242/jeb.229922

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