The Effectiveness of Whole Body and Localized Measures of Fatigue

Abstract

Localized muscle fatigue in the back, with a resulting decrease in muscle force production, may increase risk of injury. Numerous methods have been used to assess fatigue in the back during materials handling, but many of these methods remain questionable as to what they are actually measuring. The goal of this study was to compare five different methods for measuring fatigue resulting from dynamic lifting, and to determine which methods correlate best with fatigue. Eight subjects performed sagittally symmetric lifts at a frequency of 12 lifts per minute for 60-minutes. Throughout the experiment, VO₂, heart rate, local muscle oxygenation measured by Near Infrared Spectroscopy (NIRS), and subjective feedback was recorded. The whole body measures, VO₂ and heart rate, were weakly correlated with the localized measures of NIRS and spectral analysis. Few of these correlations were significant, and none showed strong relationships. The subjective measures correlated well with NIRS. The results of this study suggest current measures of fatigue may not assess the risk of fatigue to a particular muscle. It is important that more comparative studies are done to better the understanding of fatigue and what is being measured by common measures of fatigue. Additional studies should be done, particularly for the more quantitative, localized, measures such as NIRS.