Neuromuscular mechanisms underlying rhythmic auditory stimulation revealed through muscle synergy and intermuscular...

Rhythmic Auditory Stimulation (RAS) has been shown to enhance gait function and rhythmic motor control in neurological populations by modulating neural circuits responsible for movement coordination. However, the underlying physiological mechanisms, particularly regarding muscle synergy and neural drive, remain insufficiently understood.

How does RAS influence gait rhythmicity and neuromuscular coordination, as reflected in muscle synergy and intermuscular coherence?

Twenty-five healthy young adults performed gait trials under two conditions: without auditory cues (noRAS) and with individualized metronome-paced RAS. Healthy adults were selected to minimize potential confounding and to provide a normative reference for muscle synergy and intermuscular coherence metrics. Surface EMG from seven lower-limb muscles and foot pressure data were recorded. Gait speed and stride time variability were calculated. Muscle synergies were extracted using non-negative matrix factorization, with VAF₁ used to assess muscle coordination complexity. β-band (15-30 Hz) intermuscular coherence was analyzed during mid-stance to pre-swing and swing phases. Paired t-tests and Pearson's correlations were used for comparison and association analyses.

No significant differences in gait speed, stride time variability, or VAF₁ were found between conditions. However, changes in stride time variability were significantly correlated with β-band coherence in specific muscle pairs: VM-HAM during mid-stance to pre-swing (r = 0.55, p < 0.01); TA-HAM (r = 0.47, p < 0.05), VM-VL (r = 0.44, p < 0.05), and TA-SOL (r = -0.46, p < 0.05) during swing.

RAS may enhance gait rhythmicity by modulating corticospinal drive and improving phase-specific neural coordination. Combined synergy and coherence analyses offer valuable insight into RAS-induced neuromuscular adaptations.