Lower‑Limb Surface Electromyographic Differences in Roundhouse Kicks between Elite and Sub‑Elite Taekwondo Athletes: A Functional Principal Component Analysis

Jianbo Sun^1*Yifei Wang²Jingyuan Sun¹Delong Dong³

• ¹Hospital Universiti Sains Malaysia, Health Campus, Universiti Sains Malaysia, Kota Bharu, Malaysia
• ²Qufu Normal University, Qufu, China
• ³Ludong University, Yantai, China

Purpose: This study aimed to investigate the functional characteristics and distinctions in lower-limb electromyography (EMG) time-series data during roundhouse kicks performed by elite (n = 10) and sub-elite (n = 10) Taekwondo athletes, using Functional Principal Component Analysis (FPCA) to extract key parameters and identify critical phases of movement. Methods: EMG signals from 16 lower-limb muscles were collected via a Noraxon system synchronized with Vicon 3D motion capture. Group differences in integrated EMG (iEMG) were assessed using ANOVA, and muscles showing significant differences were further analyzed with FPCA (smoothing parameter e⁻⁷; eigenvalues > 1; cumulative variance > 85%). Results: Elite athletes demonstrated significantly higher iEMG values in specific muscles of both the supporting and kicking legs (p < 0.05). FPCA revealed higher scores for selected muscle components in the supporting and kicking legs among elite athletes (p < 0.05, ES = 0.64, R² = 92.6%; p < 0.05, ES = 0.66, R² = 88.8%; p < 0.01, ES = 0.53, R² = 94.8%). Notably, PC5 of the biceps femoris in the kicking leg was prominent during the kicking phase, while PC 4 of the gluteus maximus and biceps femoris in the supporting leg was critical during the recovery and end phases. Conclusion: These findings highlight muscle-specific contributions that differentiate kick quality between top-level and average athletes. FPCA offers a novel framework to assess movement quality, providing insights for technique improvement and supporting the development of automated performance evaluation systems in combat sports.