Statistical Parametric Mapping reveals sex-specific, phase-dependent differences in bilateral three-dimensional ground reaction force during Wushu Changbing PiJi in high-level athletes

PiJi is a core attacking technique in Wushu Changbing competition, but continuous waveform evidence remains limited regarding the sex-specific phase characteristics of bilateral 3D ground reaction force (GRF) during PiJi performed with maximal voluntary effort (MVE). This study aimed to compare continuous changes in trailing-foot, lead-foot, and net bilateral GRF between high-level male and female athletes during PiJi performed with MVE. In this cross-sectional, laboratory-based observational study, 44 right-hand-dominant athletes, including 22 male athletes and 22 female athletes, performed PiJi with MVE, yielding 616 valid trials. Bilateral 3D GRF was recorded using two force plates. Each trial was time-normalized and linearly interpolated to 143 equally spaced nodes, and within-participant mean waveforms were calculated before between-group differences were analyzed using statistical parametric mapping. Primary analyses used random-field-theory inference, with sensitivity examined using 5,000 permutation tests. After Bonferroni correction, phase-specific sex differences were detected in trailing-foot, lead-foot, and net bilateral 3D GRF. Scalar localization showed that male athletes had higher trailing-foot F y during the middle phase (33.98%–47.04%) and higher trailing-foot F x (62.41%–71.99%) and net bilateral F x (54.18%–70.41%) during the middle-to-late phase; female athletes showed only a brief period of higher trailing-foot vertical F z during the middle phase (42.11%–44.61%). Although lead-foot 3D GRF differed overall, no confirmatory difference was localized to any single scalar component. These findings indicate that sex-related GRF differences in high-level PiJi were concentrated mainly in specific horizontal-plane phases of trailing-foot and net bilateral force, whereas the lead-foot difference was identified only at the overall 3D GRF level. These results provide kinetic evidence for phase-specific assessment of PiJi technique and suggest that training monitoring and mechanistic research should consider foot, direction, and movement phase rather than relying only on peak force or discrete variables. Future studies integrating multimodal measures and sport-specific performance may further clarify the functional significance of bilateral force-generation patterns.