Muscle fatigue and endurance during repetitive intermittent static efforts: development of prediction models

Abstract

Localized muscle fatigue has received growing attention as a potential design variable and exposure metric in research towards prevention of musculoskeletal disorders in the workplace. While fatigue during sustained static work has been investigated extensively, effects during tasks comprising work-rest cycles are less clear. Work-rest models for static intermittent work have been presented in several reports, but the applicability is often limited to specific conditions. A study was conducted that facilitated a description of the relationships between static intermittent efforts and muscle endurance and fatigue. Exercises consisted of 1 h (maximum) of repetitive static arm abductions, involving a range of muscle contraction levels (10-30% maximum voluntary exertion), duty cycles (0.2-0.8) and cycle times (20-180 s). A between-subject central composite experimental design was used and 15 different exercise conditions were examined with six participants (three females and three males) for each. Along with endurance times, temporal changes related to fatigue were monitored using muscle strength, ratings of discomfort and electromyography (EMG) obtained from the middle-deltoid muscle during the contraction phase of the work cycles. The results of this study showed the influence of contraction level and duty cycle on the majority of fatigue measures used, while cycle time tended to affect EMG spectral measures. Using a response surface methodology, several fatigue prediction models and contour plots were developed that can be employed as an aid for design and evaluation of light repetitive static tasks. Good correspondence was generally found between discomfort rating and other measures of fatigue, suggesting the usefulness of this measure for rapid assessments of local fatigue in the workplace.

Task variation during simulated, repetitive, low-intensity work – influence on manifestation of shoulder muscle fatigue, perceived discomfort and upper-body postures

“…Sundelin (1993) showed beneficial effects of short interruptions on both perceived fatigue and EMG manifestations of muscle fatigue. However, there are also studies, partly in line with our results, that showed no significant responses to passive or active interruptions (Mathiassen 1993;Mathiassen and Winkel 1996;Rissén et al 2002;Iridiastadi and Nussbaum 2006). In line with the findings of Crenshaw, Djupsjöbacka, and Svedmark (2006), we found that active task variation provides more opportunities for the musculoskeletal system to recover, represented as significantly less discomfort development.…”

“…It might be that task variation was too short to reduce the amount of active motor units (Moritani and Muro 1987). Iridiastadi and Nussbaum (2006) suggested that different muscle compartments or adjacent synergistic muscles are activated over time, which may have led to the absence of changes indicating muscle fatigue in the whole target muscle.…”

Characteristics of power spectrum density function of EMG during muscle contraction below 30%MVC

“…Parameters used in this analysis have been, in addition to amplitude, those that describe mean frequency (MPF) and median frequency (MF) of the power spectrum density function (PSDF) and the number of crossings of the EMG signal through the zero level (Cook et al, 1998;De Luca, 1997;Hägg and Suurkü la, 1991;Masuda et al, 1999;Pincivero et al, 2006;Coorevits et al, 2005;Hummel et al, 2005;Iridastadi and Nussbaum, 2006). Parameters MF and MPF are well accepted as indicators of muscle fatigue at higher levels of muscle contraction (Crenshaw et al, 1997;Gayda et al, 2005;da Silva et al, 2005;Beck et al, 2004;Piscione and Gamet, 2006).…”

A study to compare the pain, discomfort and tiredness between straight stick and single-incision laparoscopic surgery: an in vitro study

“…Repetitive intermittent static movements cause muscle fatigue, and this correlates with discomfort scores [11]. A study to predict musculoskeletal discomfort using Borg CR10 scales showed that trunk inclination and handling frequency are the major determinants of musculoskeletal discomfort [13].…”