Biomechanical Responses to Level, Uphill, and Downhill Running Segments During an Outdoor Marathon

ABSTRACT This study investigated running biomechanics across varying slopes during a mass‐participation road marathon. Although laboratory studies suggest specific gait modifications occur in response to varying slopes, data from outdoor competitive environments remain scarce. We monitored 39 distance runners using shoe‐mounted inertial measurement units to capture spatiotemporal, footstrike, and wearable‐derived loading data across level, uphill (+3%), and downhill (−3%) segments of the 2025 Hong Kong Marathon. Results demonstrated slope‐dependent modifications, with uphill running characterized by slower velocity (−0.29 m/s, Cohen's d  = −1.98), shorter stride length (−0.15 m, d  = −1.55), and lower cadence (−5.00 steps/min, d  = −1.21) compared with level ground ( p  d  = 1.48) and a more posterior footstrike pattern downhill ( d  = −0.62) relative to level running ( p  < 0.05). Analysis of wearable‐derived loading metrics showed no differences across slope conditions once running velocity was included as a covariate. Running velocity emerged as the primary determinant of braking, impact, and shock accelerations, indicating that differences in self‐selected running velocity may contribute substantially to loading responses across varying slopes during overground running. These findings highlight a discrepancy between controlled laboratory simulations and competitive overground running, emphasizing the role of wearable technology in capturing ecologically valid gait alterations to different terrains.