The manipulation of midsole properties to alter impact characteristics in walking

The midsole of footwear can provide an opportunity to attenuate the impact at the foot-ground interface. The present study was undertaken to quantify impact in walking in different footwear midsoles, comparing footwear thickness and hardness variations. Methods: Footbed thickness (28–41 mm) and hardness (30–55 Shore A) were varied independently in seven flip-flops. Thirteen subjects walked in the footwear variations on a level walkway in the gait laboratory as lower limb kinematics, vertical ground reaction force and peak positive axial tibial acceleration were quantified. Peak magnitude and time of the acceleration were quantified and the heel-strike transient was characterised for comparison between conditions with a repeated-measures analysis of variance (ANOVA). Thickness and hardness variations were also compared using a drop-test protocol to replicate walking. Results: Lower limb joint angles did not vary at heel-strike, however, a faster vertical heel-velocity was recorded in the softer midsoles (e.g. 55 Shore A = -0.294±0.055, 30 Shore A = -0.328±0.052, p