Background: Self-paced treadmill walking may modify gait biomechanics and neuromuscular control compared with overground walking. Whether these adaptations involve only the execution of gait or also a reorganization of its underlying modular motor control remains unclear. We compared overground 10-Meter Walk Test (10MWT) and MoonWalker self-paced treadmill walking by integrating kinematics, surface electromyography (sEMG), and muscle-synergy analysis.

Methods: Up to 19 participants with paired 10MWT and MoonWalker recordings were analyzed according to data availability. Lower-limb and trunk kinematic trajectories and MVC-normalized sEMG envelopes were time-normalized to 0–100% of the gait cycle. EMG preprocessing included band-pass filtering, full-wave rectification, low-pass filtering, and normalization to muscle-specific MVCs. Condition-dependent differences across the gait cycle were assessed using paired cluster-based permutation testing with correction for multiple comparisons. Muscle synergies were extracted through non-negative matrix factorization in participants with complete bilateral EMG datasets.

Results: MoonWalker walking induced clear phase-dependent modifications in lower-limb kinematics. Significant clusters showed greater ankle dorsiflexion, reduced femoral and knee pitch during specific gait-cycle phases, and phase-dependent hip adaptations, whereas trunk kinematics did not significantly differ between conditions. Significant neuromuscular changes were also observed at the single-muscle level, with lower MoonWalker activation of bilateral rectus femoris during early gait-cycle phases, bilateral medial gastrocnemius during mid-cycle, and right tibialis anterior during initial and terminal portions of the gait cycle. In contrast to these biomechanical and muscle-specific adaptations, muscle synergy organization was preserved between conditions. The same modular structure was identifiable during 10MWT and MoonWalker walking, and synergy-level comparisons revealed no significant between-condition differences.

Conclusions: Self-paced treadmill walking modifies gait execution through phase-specific changes in joint kinematics and individual-muscle activation, while preserving the underlying muscle-synergy organization. These findings suggest that the locomotor environment influences how an established motor-control strategy is expressed, rather than inducing a substantial reorganization of its modular neuromuscular structure.