Sex-specific metabolic and biomechanical responses to advanced footwear technology

Recent retrospective analyses of elite distance running performances reveal a larger impact of advanced footwear technology (AFT) on female runners, though female runners remain underrepresented in laboratory AFT research and few sex comparisons have been made. The purpose of this study was to compare sex-specific metabolic and biomechanical responses to AFT versus traditional racing flats. We hypothesised that female runners would have relatively larger differences in metabolic expenditure and biomechanical differences between footwear. Collegiate and competitive cross-country runners (male: n = 15; female: n = 10) completed laboratory testing in the Nike Vaporfly Next% 3 (VP) and Nike Rival Waffle 5 (FL). Runners completed two 3-minute trials at a self-selected race pace, one per shoe, on an instrumented treadmill with kinematics and kinetics recorded. Biomechanical differences between shoes (DBS) were calculated. Subsequently, four 5-minute trials at a self-selected submaximal pace, two per shoe, were completed to quantify metabolic improvements from VP (VP% benefit). These outcomes were compared using ANCOVA models to determine the effects of sex, covarying for speed. Multiple partial correlations were calculated between VP% benefit and biomechanical DBS variables. A main effect of sex (p = 0.049) was observed for VP% benefit quantified from energetic cost; females benefitted (4.66 ± 2.40%) more than males (2.79 ± 1.99%). Without covarying for speed this main effect was insignificant (p = 0.054). Main effects of sex were observed among DBS variables: ankle dorsiflexion (p = 0.026), metatarsophalangeal (MTP) joint positive (p = 0.010), MTP negative power (p = 0.031), and propulsive force (p = 0.022). Female runners had larger MTP power responses to AFT controlling speed effects, suggesting that female MTP mechanics are more responsive to AFT characteristics. Correlations suggest that biomechanical responses to VP separating high versus low metabolic responders may be sex specific.