Reduced firing rates of high threshold motor units in response to eccentric overload

Citation

Balshaw T, Pahar M, Chesham R, Macgregor LJ & Hunter A (2017) Reduced firing rates of high threshold motor units in response to eccentric overload. Physiological Reports, 5 (2), Art. No.: e13111. https://doi.org/10.14814/phy2.13111

Abstract
Acute responses of motor units were investigated during submaximal voluntary isometric tasks following eccentric overload (EO) and constant load (CL) knee extension resistance exercise. Ten healthy resistance-trained participants performed four experimental test sessions separated by 5 days over a 20 day period. Two sessions involved constant load and the other two used eccentric overload. EO and CL used both sessions for different target knee eccentric extension phases; one at 2 sec and the other at 4 sec. Maximal voluntary contractions (MVC) and isometric trapezoid efforts for 10 sec at 70% MVC were completed before and after each intervention and decomposed electromyography was used to measure motor unit firing rate. The firing rate of later recruited, high-threshold motor units declined following the 2-sec EO but was maintained following 2sec CL (P < 0.05), whereas MUFR for all motor units were maintained for both loading types following 4-sec extension phases. MVC and rate of force development where maintained following both EO and CL and 2 and 4 sec phases. This study demonstrates a slower firing rate of high-threshold motor units following fast eccentric overload while MVC was maintained. This suggests that there was a neuromuscular stimulus without cost to the force-generating capacity of the knee extensors. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Keywords
Decomposed electromyography; lengthening contractions; MVC

Journal
Physiological Reports: Volume 5, Issue 2

People

Professor Angus Hunter

Honorary Professor, FHSS Management and Support

Dr Lewis Macgregor

Lecturer in Physiology and Nutrition, Sport