Abstract
Studies have shown that muscle fatigue can lead to posture, joint angle, inter-joint coordination and variability alterations. However, the three-dimensional kinematic effects of localized muscular fatigue on a multijoint movement remain unclear. Healthy young adults (N = 17, 10 females) performed a standing repetitive pointing task when they were non-fatigued, and after localized muscle fatigue was induced at the elbow, the shoulder, and the trunk using isometric protocols performed until exhaustion. Joint angles and angular standard deviation (SD) of trunk, shoulder and elbow, and continuous relative phase (CRP) and CRP SD between trunk and shoulder, and shoulder and elbow were computed and compared between fatigue conditions. Results showed that trunk lateral flexion SD increased after fatigue of the elbow (0.1°, p = 0.04), shoulder (0.1°, p = 0.04) and trunk (0.1°, p<0.01). However, fatigue at different muscles brought different kinematic changes. Shoulder fatigue induced the greatest overall changes, with angular changes at all three joints. Trunk fatigue increased the shoulder horizontal abduction SD, elbow flexion SD and trunk-shoulder CRP. Elbow fatigue induced angular changes at trunk, shoulder and elbow, but did not affect CRP or CRP SD. This study highlights the crucial role of trunk variability in compensating for localized muscle fatigue during a repetitive upper limb task performed while standing.
Highlights
Repetitive upper limb movements are regularly performed in varieties of jobs as well as in the activities of daily living
The trunk lateral flexion mean angle was smaller after shoulder fatigue than it was after EF (4.4 ̊ smaller than after EF, p
This study shows that localized muscle fatigue at either trunk, shoulder or elbow increases trunk lateral flexion variability in the repetitive pointing task
Summary
Repetitive upper limb movements are regularly performed in varieties of jobs as well as in the activities of daily living. Sustained repetitive movement is associated with musculoskeletal disorders (MSDs) [1, 2]. MSDs of the upper limb and trunk accounted for 53% of the 240,682 lost time claims in Canada in 2016 [3]. The huge economic burden that MSDs have brought to our society cannot be ignored. Muscular fatigue is one of the most important factors contributing to the development of MSDs [4]. A better understanding of the mechanisms of muscular fatigue would help us better understand the mechanism of MSDs, which could help their prevention
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