Analysis on the mechanism of speed skaters’ skating sagittal trunk flexion angle control and wind resistance coefficient change on skating efficiency

Optimising trunk posture is critical for improving efficiency in speed skating, as it influences both aerodynamic drag and neuromuscular demands. This study aimed to quantify how incremental changes in sagittal trunk flexion angle affect aerodynamic resistance, muscular load, and overall skating efficiency under race-relevant conditions. Twenty-eight elite male speed skaters performed trials across straight and curved tracks at sagittal trunk flexion angles ranging from 30°to 50°. Trunk kinematics were captured using inertial measurement units, muscular activity was recorded with surface electromyography, and drag coefficients were estimated through computational fluid dynamics simulations. These datasets were integrated within the Real-Time Integrated Trunk–Cd–Efficiency (RITCE) model to evaluate the combined biomechanical and aerodynamic effects. Results showed that efficiency decreased significantly from 82.1% at 30° to 75.3% at 50° ( p < 0.001), while drag coefficient increased from 0.241 to 0.276 ( p < 0.001) and EMG load rose from 100.2 to 130.9 µV ( p < 0.001). Fatigue indices and co-contraction ratios also increased with deeper trunk flexion. Efficiency was consistently lower on curved tracks, with significant sagittal trunk flexion angle–track interactions observed. These findings demonstrate that excessive trunk flexion imposes aerodynamic, neuromuscular, and mechanical penalties, supporting the need for trunk-targeted biomechanical interventions to enhance skating efficiency in elite athlete.