Impact of running speed and footstrike type on foam compression in Advanced Footwear Technology

Recent developments in racing footwear have altered running mechanics, performance, and economy. Measuring the foam deformation under the forefoot and heel may help understand what makes advanced footwear technology (AFT) so effective. This study investigates a novel measurement technique to dynamically observe midsole thickness. Thirty-three participants (15 women and 18 men) wore AFT instrumented with hall effect sensors and magnets–one under the forefoot and one under the heel–and ran two 30 s trials (3.35 m/s and 4.47 m/s) on a treadmill. Both the timing and magnitude of peak compression were calculated from the deformation curves. Non-rearfoot strike (NRFS) runners had 1 mm (7.0%) greater forefoot foam compression (p < 0.001) and 49% as much heel foam compression (p < 0.001) compared to rearfoot strike (RFS) runners. Foam compression under the forefoot (p = 0.006) and heel (p = 0.006) significantly increased as speed increased. When running faster, the percent of time to peak compression was greater under the heel (p = 0.009), but not under the forefoot (p = 0.983). This study successfully measured midsole foam compression under the forefoot and heel during running using a relatively low-cost method. Using this new method produces measurements not previously recorded. As a second purpose to this study, we found speed and footstrike types utilise the foam differently leading to potential understanding in how the foam stores and releases energy. Better characterising AFT midsole foam compression profiles of individual runners may aid in understanding how metabolic benefits differ within and between footstrike groups.