Sex Differences in Speed-Related Running Mechanics Using IMU in Runners.

OBJECTIVE: The aim of this descriptive study was to evaluate lower-limb biomechanical parameters in runners of different sexes and analyse how these parameters are modulated across three intensities (65%, 85% and 100% maximal aerobic speed [MAS]). METHODS: One hundred recreational runners (50 women, 50 men) completed a 2000-m time trial to determine MAS, followed by three 2-min treadmill bouts at 65%, 85% and 100% MAS. Kinematic and mechanical variables were recorded using the RunScribe™ inertial measurement system, with sensors positioned bilaterally on the shoes and on the sacral region. RESULTS: Linear mixed-effects models showed a significant main effect of speed condition for most biomechanical outcomes. As speed increased from 65% to 100% MAS, runners showed shorter contact time and greater flight time, stride length, step rate, braking Gs, peak vertical ground reaction force, loading rates, shock, total shock and max pronation velocity. A significant main effect of sex was observed for several variables: men showed higher BG, flight time, stride angle, stride length, peak vertical ground reaction force, leg spring stiffness, loading rates and max pronation velocity, whereas women showed longer contact time. Sex × speed interactions were significant only for shock, total shock and max pronation velocity, indicating that most speed-related adaptations occurred in a similar direction in men and women. CONCLUSIONS: These findings provide a descriptive characterisation of sex- and speed-related IMU-derived running mechanics in runners. Standardised treadmill testing across relative intensities may help characterise how lower-limb mechanics are modulated by sex and running speed. Because injury incidence, running economy, race performance and longitudinal adaptations were not assessed, braking- and impact-related variables should be interpreted as hypothesis-generating rather than as evidence of injury risk or performance.