Adaptation-dependent modulation of coordinated muscle activities in human gait adaptation as revealed by tensor decomposition

Extensive research has explored muscle synergies as a strategy for managing motor redundancy and motor adaptation as a process for adjusting to novel environments. However, the relationship between these two fundamental concepts remains unclear. To address this gap, we analyzed muscle activity during split-belt treadmill walking adaptation using tensor decomposition. Our results reveal that two specific synergies-one associated with the fast limb and the other with the slow limb-are strongly recruited at the onset of adaptation and decline over time. The fast-limb synergy is active during single support, whereas the slow-limb synergy is engaged during double support. Additionally, another synergy is modulated during the washout phase. While a subset of synergies shows adaptive changes, most remain stable, maintaining balance between flexibility in gait modification and overall locomotor stability. These findings highlight distinct roles of muscle synergies across limbs and learning phases, offering insights into the neural mechanisms underlying motor adaptation.