ABSTRACT
Localized muscle fatigue (LMF) is of significant interest to many professionals, including ergonomists, for safety interventions. In the literature, many indices have been used to indicate LMF. However, no gold standard could be identified. For determining a standard indicator for LMF, nine subjects were required to exert their previously measured maximal voluntary contraction (MVC) and 40% MVC in elbow flexion for as long as they could. Their magnitude of force of exertion, electromyograph (EMG) amplitude, median frequency (MF), muscle bed blood volume (BV), and muscle oxygenation were measured for MVC. Similarly, the muscle force exertion, EMG amplitude, MF, BV, oxygenation, oxygen uptake, ventilation volume, and heart rate were
measured for 40% MVC. Rate of perceived exertion (RPE), visual analog score (VAS), and body part discomfort rating (BPDR) were measured for both contractions. The obtained data were subjected to analysis of variance (ANOVA) with repeated measures correlation analysis to determine correlation between force of contraction and independent variables. A regression analysis was carried out to predict the force from independent variables. The mean MVC and durations of hold scores were (with standard deviations) 197.6 N (25.9 N) and 58.15 s (17.6 s), respectively. The corresponding 40% MVC values were 79 N (10.4 N) and 275 s (35.8 s). The ANOVA revealed that the values at different percentiles of the task cycles were significantly different for both contraction levels (
p
< .001). The MF was the strongest indicator of LMF in MVC (
r
= 0.91,
p
< .001), but in the 40% MVC contraction, the VAS score was better. None of the variables were found to consistently represent LMF in different levels of muscle contraction. A different grouping of objective and subjective variables for MVC and 40% MVC increased the predictability of force over the single variables mentioned before. A gold standard for representing LMF still eludes us.
