Generalization of motor module recruitment across standing reactive balance and walking is associated with beam walking performance in young adults.

Background: Recent studies provide compelling evidence that recruiting a common pool of motor modules across behaviors (i.e., motor module generalization) may facilitate motor performance. In particular, motor module generalization across standing reactive balance and walking is associated with both walking speed and endurance in neurologically impaired populations (e.g., stroke survivors and individual's with Parkinson's disease). To test whether this phenomenon is a general neuromuscular strategy associated with well-coordinated walking and not limited to motor impairment, this relationship must be confirmed in neurologically intact adults.
Research Question: Is motor module generalization across standing reactive balance and walking related to walking performance in neurologically intact young adults?
Methods: Two populations of young adults were recruited to capture a wide range of walking performance: professionally-trained ballet dancers (i.e., experts, n = 12) and novices (n = 8). Motor modules (a.k.a. muscle synergies) were extracted from muscles spanning the trunk, hip, knee and ankle during walking and multidirectional perturbations to standing. Motor module generalization was calculated as the number of modules common to these behaviors. Walking performance was assessed using self-selected walking speed and beam-walking proficiency (i.e., distance walked on a narrow beam). Motor module generalization between experts and novices was compared using rank-sum tests and the association between generalization and walking performance was assessed using correlation analyses.
Results: Experts generalized more motor modules across standing reactive balance and walking than novices (p = 0.009). Across all subjects, motor module generalization was moderately associated with increased beam walking proficiency (r = 0.456, p = 0.022) but not walking speed (r = 0.092, p = 0.349).
Significance: Similar relationships between walking performance and motor module generalization exist in neurologically intact and impaired populations, suggesting that motor module generalization across standing reactive balance and walking may be a general neuromuscular mechanism contributing to the successful control of walking.
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