CRP-derived lower-limb coordination pattern distributions and frequency-band trunk-lower limb intermuscular coherence during badminton backhand footwork: a cross-sectional study

To compare complete-cycle lower-limb coordination-pattern distributions and frequency-band-specific trunk-lower limb intermuscular coherence during a standardized badminton backhand footwork-backhand-clear task between elite and amateur players.

Thirty-six male badminton players were classified into elite and amateur groups (n=18 each). Each participant completed 10 valid trials. Three-dimensional kinematics and surface electromyography were synchronously recorded using Qualisys and Delsys Trigno systems. Continuous relative phase waveforms were summarized as four coordination-pattern percentages for the hip-knee, hip-ankle, and knee-ankle pairs. Intermuscular coherence was quantified as the area of significant coherence (AZ) for 21 trunk-lower limb muscle pairs across α, β, and γ bands. Trial-level linear mixed-effects models included group, trial, and their interaction as fixed effects and participant as a random intercept. Years of badminton training were not included as a covariate, as the objective was to compare competitive-level groups within their existing training backgrounds. Benjamini-Hochberg false discovery rate (FDR) correction was applied separately to 12 coordination and 63 coherence comparisons.

After FDR correction, elite players showed higher hip-knee in-phase and lower anti-phase proportions, higher proximal-dominant and lower distal-dominant proportions for hip-ankle and knee-ankle coordination, and a higher knee-ankle anti-phase proportion (all q=0.025). Although 23 coherence comparisons had raw P<0.05, none survived FDR correction (all q≥0.098).

Elite and amateur players differed in selected complete-cycle coordination-pattern distributions, with greater proximal contribution to hip-ankle and knee-ankle coordination in elite players. No muscle-pair-frequency-band coherence difference remained significant after FDR correction. These task-specific, cross-sectional findings do not identify the timing of coordination differences, establish causal effects of training, or demonstrate competitive-level associations independent of training duration.