Author(s): FAVENNEC, A., MORNIEUX, G.1,2, FRÈRE, J.3, Institution: UNIVERSITÉ DE LORRAINE, Country: FRANCE, Abstract-ID: 1621

INTRODUCTION:
Back exoskeletons are wearable structures that give an assistive torque to one or multiple joints and can prevent from low back disorders during manual handling tasks (1). But, the change in external constraints has been shown to modify the motor behaviour during familiarization to a soft back exoskeleton while performing manual handling tasks (2). However, little is known about the likely changes in central command during familiarization. Therefore, the aim of this study was to assess the modulation of muscle synergies during a familiarization to a soft back exoskeleton with manual material handling.
METHODS:
Eighteen males (21.5 ± 2.3 years, 178.3 ± 3 cm, 69.6 ± 6.2 kg) were recruited to perform 6 sessions of one hour of familiarization to the CORFOR® V2 soft back exoskeleton (2). This protocol consisted in several manual handling and precision tasks involving trunk bending. During measurements carried out at baseline and at the end of each session, participants were asked to handle a box (8 kg; 15 cycles / min) using STOOP and SQUAT techniques. Surface electromyography (sEMG) signal was unilaterally recorded on 14 muscles of the lower limb, trunk, back and upper-limb. From sEMG linear envelopes, muscles synergies were extracted for each session through non-negative matrix factorization. The effect of the familiarization was assessed using a repeated measures ANOVA to identify any change in the number of synergies, their composition (motor module similarity) or their activation coefficients (center of activation, full width at half maximum and variance ratio).
RESULTS:
Results showed that 2 synergies explained 91 ± 1.8 % of the variance for both STOOP and SQUAT tasks during the whole familiarization. For both STOOP and SQUAT, synergy 1 was activated during the downward phase while synergy 2 was activated during the upward phase. Over the familiarization, the motor modules remained similar, for both STOOP (0.91 ± 0.13) and SQUAT (0.86 ± 0.17) tasks. There was no statistical evidence of change in the muscle synergy activations across the sessions, whatever the metric analyzed, for both STOOP and SQUAT tasks.
CONCLUSION:
Overall, it appears that the muscle synergies extracted were robust throughout the familiarization protocol, despite a known effect of this soft back exoskeleton on joint kinematics, perceived comfort and lumbar spine loads (2, 3). According to previous results (4), these results suggest that the exoskeleton used in this study did not bring sufficient perturbations to change the central command.
REFERENCES:
1) De Looze et al., Ergonomics, 2016.
2) Favennec et al., Applied Sciences, 2024.
3) Favennec et al., Computer Methods in Biomechanics and Biomedical Engineering, 2024.
4) Hug et al., Journal of Neurophysiology, 2011.