Indices of Muscle Fatigue

Abstract

The objective of the study was to determine if any of the many indicators of localized muscle fatigue (LMF) mirrors the decline in force more closely (gold standard). If not, can a group of indicators can predict LMF better? Nine normal young subjects were required to exert their maximal voluntary contraction (MVC) and 40% of MVC in elbow flexion as long as they could. The magnitude of the force, EMG amplitude, median frequency (MF), muscle bed blood volume, and muscle oxygenation were measured for MVC. For the 40% MVC contraction in addition to the foregoing variables oxygen uptake (V0₂), ventilation volume and heart rate were also measured. The rate of perceived exertion (RPE), visual analog score (VAS) and body part discomfort rating (BPDR) were measured for both contractions. Data were subjected to the analysis of variance (ANOVA) with repeated measures, correlation and regression analysis. Different percentiles of the tasks were significantly different in both contractions (p<0.001). The MF was the strongest indicator of the force decline in MVC (r = 0.91; p<0.001) but in 40% MVC the VAS was a better indicated. None of the variables consistently represented LMF in different levels of contraction. A different grouping of objective and subjective measures for MVC and 40% MVC increased the predictability of the force decline (LMF).