Factors influencing corticomuscular coherence for axial and lower limb musculature in a healthy population: a scoping review.

Introduction: Corticomuscular coherence (CMC) quantifies the frequency-specific coupling between cortical and muscular activity and is increasingly used to probe motor-control mechanisms. However, the factors that consistently influence CMC in axial and lower-limb muscles remain unclear. Objective: The objective of this study is to map and critically describe experimental factors and methodological choices that have been studied and their potential influence on CMC of axial and lower limb muscles measured in healthy humans. Methods: A scoping review was conducted following PRISMA-ScR guidelines. CINAHL, MEDLINE (Ovid), Embase, and Web of Science were searched from the date of inception to March 5th, 2024. Eligible studies that (i) computed CMC, (ii) recorded cortical activity with EEG or MEG, (iii) analyzed trunk or lower limb EMG, and (iv) compared CMC across experimental conditions or participant groups were included. Two reviewers independently screened records, extracted demographic, neurophysiological, task, and signal-processing variables, and grouped studies by the factor examined; third reviewer resolved discrepancies. Results were synthesized descriptively. Results: Four factors showed the most consistent influence on CMC: (1) Age: younger adults exhibit higher CMC than older adults (2) Muscle-specificity: the tibialis anterior (TA) displays stronger CMC than other axial or lower-limb muscles; (3) Contraction type: isotonic and eccentric/quasi-isotonic contractions elicit greater CMC than isometric contractions; (4) Athletic status: non-athletes demonstrate higher CMC than trained individuals. The effects of fatigue, contraction intensity, posture, or walking tasks were inconsistent. Methodologically, most studies employed EEG (single Cz channel) and rectified EMG; MEG, source localization, and longitudinal approaches were seldom used. Discussion: Current evidence indicates that participant characteristics (age, athletic status) and task parameters (muscle tested, contraction type) can impact CMC, but heterogeneity in study design and analysis hampers direct comparison and causal inference. Future research should adopt longitudinal designs, standardized protocols, and advanced source localization techniques to clarify the mechanisms governing CMC in axial and lower-limb musculature.