Alteration of muscle synergy structure while walking under increased postural constraints

Abstract

It is hypothesised that specific groups of muscles aka muscle synergies (MSs) are combined by the central nervous system to control a wide repertoire of movements and also simplify motor control. Therefore, studying MSs during human locomotion is of significance, as it may reveal neuromuscular strategies for postural stability. In this study, the authors aimed to use the hypothesis of MSs to identify specific muscle co-activations during overground walking and slacklining where postural perturbations were generated by the participants rather than being externally controlled. Nine participants were asked to walk overground and on a slackline while they recorded myoelectric activity of their leg muscles. They extracted synergies from the electromyography signals in the two tasks using factor analysis. The results showed adaptation in the shared MSs structure during walking on the slackline and these shared MSs across participants were recruited flexibly to meet the demand for stability. The modulation of synergies suggests adaptive neuromuscular strategies for stability while walking on a slackline. Specifically, higher activation of quadriceps during slacklining suggests a crouched gait to facilitate balance. During overground walking, lower leg muscles revealed higher activation compared to slacklining to support a more consistent toe-off during the stance phase.

Proficiency‐based recruitment of muscle synergies in a highly perturbed walking task (slackline)

“…44 Moreover, slackline as a sport may assist individuals in developing postural response that requires stability in a similar challenging situation. 1 A higher knee flexion kinematic responses to lower the Center of Mass (COM) is one such behavior that was observed previously to provide knee stability in forward motion. 1 The results from our study showed changes in the dimensionality of MS for three different groups on a novel task.…”

“…1 A higher knee flexion kinematic responses to lower the Center of Mass (COM) is one such behavior that was observed previously to provide knee stability in forward motion. 1 The results from our study showed changes in the dimensionality of MS for three different groups on a novel task. Therefore, training on a slakcline may improve the postural stability among individuals affected with ML instability by incorporating new synergies.…”

“…Also, previous studies have already examined the coordination strategy in ML direction for the same task 20 . Furthermore, on comparison between slacklining and walking from our previous study, we identified alterations in the muscle co‐activation patterns during slacklining 1 . The muscles groups that were altered mostly associated with balance control along the AP direction.…”

“…Understanding postural control strategies is crucial for human locomotion and other gross motor skills. Studies have suggested that walking on a challenging support surface while maintaining balance control causes a more arrhythmic gait pattern within a subject, 1 making it more difficult to understand coordinated activation of the muscles to maintain stability. Researchers have suggested robust muscle co-activation schemes underlying postural control which may be modularly organized as muscle synergy (MS), [2][3][4] aka movement primitives.…”

“…20 Furthermore, on comparison between slacklining and walking from our previous study, we identified alterations in the muscle co-activation patterns during slacklining. 1 The muscles groups that were altered mostly associated with balance control along the AP direction. Based on these rationales we examined the kinematics and muscle kinetics in AP direction in this study.…”