Neuromuscular Mechanisms Underlying Rhythmic Auditory Stimulation Revealed Through Muscle Synergy and Intermuscular Coherence Analyses

Abstract

BackgroundRhythmic 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.Research QuestionHow does RAS influence gait rhythmicity and neuromuscular coordination, as reflected in muscle synergy and intermuscular coherence?MethodsTwenty-five healthy young adults performed gait trials under two conditions: without auditory cues (noRAS) and with individualized metronome-paced RAS. 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. Beta-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.ResultsNo significant differences in gait speed, stride time variability, or VAF1 were found between conditions. However, changes in stride time variability were significantly correlated with beta-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.SignificanceRAS 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.

Note:
Funding declaration: This work was partly supported by Grant-in-Aid for Scientific Research (B)23K27934 and Grant-in393 Aid for Challenging Research (Exploratory) 23K18505 (to IN).

Conflict of Interests: Nothing to report.

Ethical Approval: This study was conducted with the consent of the Ethical Review Committee of Shinshu University School of Medicine (approval number: 5327).

Keywords: Rhythmic auditory stimulation, Muscle synergy, Intermuscular coherence, gait control