Impact of an occupational back-support exoskeleton on muscle synergies during a pick-up movement

Purpose: While passive back-support exoskeletons have been shown to reduce back-muscle activity during laboratory-simulated tasks, their influence on motor control is still unclear. The aim of this study was to investigate the impact of a passive back-support exoskeleton on muscle synergies, the predefined groups of coordinated muscle activations used by the central nervous system to produce natural movements. Methods: Nineteen participants performed several pick-up tasks with 500 g weights, with and without a back-exoskeleton. During these trials, surface electromyography of eight muscles involved in the task was recorded. Muscle synergies were then extracted from these signals using non-negative matrix factorization. For each participant, we computed silhouette scores and performed statistical tests to evaluate the distinction between synergies extracted from the trials with and without the exoskeleton. Results: Two to three muscle synergies were sufficient to account for the activations of the eight muscles during the movements. The inter-participant clustering of the mean synergies indicated that participants used subjective motor strategies to perform the task, and the silhouette scores highlighted differences between synergies of the two conditions for 70.6% of the participants. Conclusion: Our findings indicate that an exoskeleton can lead to a modification of muscle recruitment patterns. However, the impact of the exoskeleton on muscle synergies differed among participants, which highlights the importance of the wearer’s experience and adaptation to the equipment.