Effects of a Passive Back-Support Exosuit on Objective and Subjective Measures of Human Performance During a Simulated Bush-Crop Harvesting Task.

Abstract

Objective: Interest in wearable passive back-supports (exoskeletons/suits) has grown rapidly as a tool to reduce the risk of low back injury by reducing lumbar extensor muscle loading. Previous studies have shown the effectiveness of passive back-support exoskeleton/suit at reducing low back muscle activity/fatigue in a variety of tasks, but it is unclear whether an exoskeleton/exosuit intervention would be effective in agricultural harvesting tasks that require complex three-dimensional dynamic motions, long duration stooped postures, and variable engagement of the lower extremities. The objective of the current study was to evaluate the effects of a passive lumbar support exosuit on muscle fatigue and comfort/mobility during a simulated harvesting task in a controlled laboratory setting.

Methods: Sixteen participants were asked to perform a continuous work task that simulated a 3-min bout of harvesting from a bush crop. Participants harvested at a rate of 1 unit per 2 s and were permitted to assume any effective harvesting position except a full kneeling posture. Test contractions and subjective assessments were performed before and after each 3-min bout of a simulated harvesting task to allow for an assessment of the 1) changes in objective measures of erector spinae muscle fatigue development (both time domain and frequency domain measures of muscle fatigue) and 2) subjective measures of physical fatigue, and 3) exosuit comfort and mobility constraints.

Results: The exosuit significantly mitigated the increases in EMG amplitude in the time domain (p = .015; Cohen's d = 0.46) indicating a mitigation of muscle fatigue, but there was no significant exosuit effect on median frequency (p = .145) or perceived fatigue in the low back (p = .289). In addition, the exosuit use was associated with significant increases in perceived movement restriction (p < .001; d = 0.82) which were also manifested in terms of significant effects of the exosuit on the magnitude of the 90^th percentile of the trunk flexion (p = .027, d = 0.29).

Conclusion: The results of this study demonstrated moderate muscle fatigue reduction effects at the cost of a negative impact on objective and subjective measures of trunk motion restrictions and comfort.