Sex-related differences in coordination and variability among foot joints during running

Background: Women, as compared with men, have a higher proportion of injuries in the ankle/foot region. However, the reason for this sex-related difference in foot injuries remains unclear. Recently, joint coordination and variability of coordination have been suggested to be a critical index for defining both the state of injury and the potential risk of injury. The purpose of this study was to investigate sex-related differences in coordination and variability among the foot joints during running. Methods: Twelve healthy men and 12 healthy women ran on a treadmill. A modified vector coding technique was used to identify coordination and variability among foot joints involving the shank, rearfoot, midfoot, and forefoot segments, and categorized into the following four coordination patterns: in-phase with proximal dominancy, in-phase with distal dominancy, anti-phase with proximal dominancy, and anti-phase with distal dominancy. Results: There were no differences in all spatiotemporal parameters and in the foot strike angle between men and women. Coordination of variability of the foot joints during running was similar between men and women, but the anti-phase with proximal dominancy in proportion of frontal rearfoot-shank vs. midfoot-rearfoot couple (men; 7.2%, women; 13.9%) and midfoot-rearfoot vs. forefoot-midfoot couple (men; 18.6%, women; 39.8%) in women was significantly increased compared to that in men. Other all coordination of the foot joints during running differed between men and women, and effect sizes of these parameters were all large. Conclusion: The results may be useful for understanding the underlying mechanism contributing to differences in injury risk in men and women, and may provide novel data on foot joint coordination and variability that could be used as reference data for both biomechanical and clinical running studies.