The Role of Boot Material and Accumulated Wear on Ankle Joint Co-Contraction During Running: A Six-Month Longitudinal Study

Abstract

Background: The cumulative distance run in a given pair of running shoes is a primary determinant of a runner’s susceptibility to injury. Objectives: This study examined how accumulated mileage in military footwear affects ankle muscle co-contraction patterns during running. Methods: Fifteen healthy men each received three new pairs of combat boots made from different materials: rubber, thermoplastic polyurethane, and polyurethane (PU). Participants wore the boots regularly for 6 months. Before and after this period, surface electromyography (EMG) signals were recorded while participants ran at a fixed speed of 3.2 m/s. Ankle muscle co-contraction indices were calculated from these recordings. Data were analyzed using a two-way repeated-measures analysis of variance. Results: No significant changes were observed in general ankle co-contraction. Directed co-contraction during push-off showed a significant effect (P = 0.046, η2p = 0.125). Subsequent paired comparisons showed that PU boots elicited significantly greater co-contraction during push-off than rubber boots. A significant effect was also observed for directed ankle co-contraction during the loading response phase (P = 0.011, η2p = 0.282). Conclusions: Different boot types may influence ankle co-contraction patterns during specific phases of running. These findings underscore the importance of considering boot type and measurement time points when assessing ankle muscle activity during physical activity.