Effects of robotic exoskeleton control options on lower limb muscle synergies during overground walking: An exploratory study among able-bodied adults

Background: The effects of lower limb (L/L) control options, developed for overground walking with a wearable robotic exoskeleton (WRE), on the neuromotor control of L/L muscles [i.e., muscle synergies (MSs)] during walking remain uncertain.

Objective: To gain initial insights regarding the effects of different control options on the number of MSs at the L/L and on their muscle weighting within each MS when walking with a WRE.

Methods: Twenty able-bodied adults walked overground without and with the WRE set at two control options with a predetermined foot pathway imposed by the WRE, and at three other control options with free L/L kinematics in the sagittal plane. Surface electromyography of eight right L/L muscles was recorded. MSs were extracted using a non-negative matrix factorisation algorithm. Cosine similarity and correlation coefficients characterised similarities between the MSs characteristics.

Results: Freely moving the L/L in the sagittal plane (i.e., non-trajectory controlled options) during WRE walking best duplicated typical MSs extracted when walking without WRE. Conversely, WRE walking while fully controlling the L/L trajectory presented the lowest correlations to all MSs extracted when walking without WRE, especially during early swing and L/L deceleration.

Conclusion: Neuromotor control of L/L muscles is affected by the selected control option during WRE walking, particularly when a predetermined foot pathway is imposed.

Significance: This exploratory study represents the first step in informing the decision-making process regarding the use of different L/L control options when using WRE and calls for further research among adults with sensorimotor impairments.