Skeletal muscle fatigue and neuromuscular activation during bed rest

Abstract

Physical inactivity results in muscle atrophy, conversion to faster muscle fibers, decrements in oxidative capacity and increased muscle fatigability. These changes may alter motor unit activation and recruitment strategies utilized by the central nervous system in controlling sustained muscular force. The aim of this study was to determine the effect of 14 days of bed rest on muscular endurance and neuromuscular activation during an isometric sub‐maximal fatigue task in the soleus muscle in healthy middle‐aged adults. Surface electromyography (EMG) and torque were recorded from the soleus muscle during isometric maximal voluntary contractions (MVC) and during an isometric, 50% MVC fatigue task pre‐post 14 days of bed rest. MVC decreased by 8.7% and maximal root mean square (RMS) EMG amplitude declined by 6.4% after bed rest. Muscular endurance time decreased by 49.7% after bed rest. Mean RMS EMG amplitude during the fatigue task increased by 7.9% following bed rest and median frequency of the EMG signal during the fatigue task decreased by 17.9%. Neural adaptations during inactivity may contribute to increased muscle fatigability. Some physical activity during periods of prolonged bed rest may be necessary to preserve motor pathways, and thereby may attenuate muscle fatigue. Funded by NSBRI grant NNJ08ZSA002N (Paddon‐Jones) and by grant 1UL1RR029876‐01 from the National Center for Research Resources, NIH.