Effects of different fatigue locations on upper body kinematics and inter-joint coordination in a repetitive pointing task

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.

Fig 1. The flow chart of the data collection protocol.

The series of shoulder, elbow and lower back fatiguing protocols were performed in random order. The green lines indicate when the Borg CR10 score was asked. MVCs, NFRPT, FRPT, FRRPT stand for maximal voluntary contractions, non-fatigued RPT, Fatigued RPT, Fatigue Recovered RPT, respectively.

Fig 2. Shoulder, elbow and lower back fatiguing protocol setups.

From the figure A to C are the figures showing the shoulder, elbow and lower back fatiguing protocols, respectively.

Fig 3. Joint angles between conditions (NF vs EF vs SF vs TF).

*NF, EF, SF and TF represent non-fatigued RPT, elbow fatigued RPT, shoulder fatigued RPT and trunk fatigued RPT respectively. Angle definitions refer to the definitions by Gates et al. (2016) and We et al. (2005). The signs of trunk lateral flexion, trunk rotation, shoulder elevation, shoulder rotation and elbow abduction angles are changed to obtain the positive values. Positive values in trunk lateral flexion, trunk rotation and trunk flexion angle means bending towards the non-reaching side, rotating towards the reaching side and bending forward respectively; Positive shoulder elevation angle and shoulder rotation angle stands for humerus horizontal flexion forward, humerus elevation, humerus external rotation. Positive elbow flexion, elbow abduction and forearm rotation means forearm flexion, forearm abduction and pronation. * indicates p < 0.05, ** indicates p < 0.01.

Fig 4. Joint angular variabilities between conditions (NF vs EF vs SF vs TF).

*NF, EF, SF and TF represent non-fatigued RPT, elbow fatigued RPT, shoulder fatigued RPT and trunk fatigued RPT respectively. The letters after * above the bars indicate significant differences. * indicates p < 0.05, ** indicates p < 0.01.