Mechanical cushioning properties of running shoe constructions across loading orientations

Abstract Midsole mechanical properties are assessed in standard test methods under a single, perpendicular loading orientation, which may not capture how running shoes respond to the range of foot strike patterns encountered during running. This study aimed to examine how loading orientation affects vertical stiffness, peak displacement, and energy return in six running shoes with different midsole materials (ethylene-vinyl acetate [EVA] and polyether block amide [PEBA]), stack height and hardness. Each shoe was loaded to a peak force of 1500 N with a mechanical last at three orientations: 15° dorsiflexion, 0° neutral, and 15° plantarflexion for 25 cycles at each orientation. Descriptive statistics and multivariable mixed models were used to describe the effects of loading orientation, midsole construction and loading cycle on the three outcomes. In both models, dorsiflexion and plantarflexion were associated with lower stiffness (Model 1: β = −72 and − 37 N mm −1 , Model 2: −26 and − 3 N mm −1 ) and greater peak displacement (Model 1:+8.6 and + 2.4 mm, Model 2: +8.3 and + 2.3 mm) compared to neutral (all p < 0.01). Energy return was least affected by loading orientation with greatest variance in response explained by shoe constructions. Drift in peak displacement and energy return across the 20 analysed cycles was small and linear, subtly altering the magnitude of response but not the nature of the response. These findings suggest that single-orientation testing may not fully represent how shoes behave across the loading orientations associated with different foot strike patterns.