Kinematic coordination in the rearfoot, midfoot, and forefoot differs depending on subgroups based on foot stiffness...

This study aimed to classify subgroups of healthy young adults based on foot stiffness and related kinetic parameters during gait, as well as to analyze intra-foot sagittal kinematics within each subgroup. Data were collected from 25 males and 24 females using a 3D motion capture system, which measured the rearfoot, midfoot, and forefoot segments. Cluster analysis identified three subgroups based on the following variables: the truss coefficient, windlass coefficient, forward component of ground reaction force (F-GRF), and ankle plantar flexion power. Group 1 demonstrated the highest foot stiffness, as indicated by the largest truss coefficient, while Groups 2 and 3 exhibited lower stiffness, characterized by greater dorsiflexion of the midfoot and forefoot relative to the rearfoot during the stance phase. Additionally, the kinematic coordination patterns between the rearfoot-midfoot and midfoot-forefoot of Groups 2 and 3 during the early and late stance phases showed significant variation. Group 3, in particular, exhibited lower F-GRF and ankle plantar flexion power than Groups 1 and 2. These results suggest that midfoot movement during the late stance phase is critical in generating foot stiffness, with a midfoot-dominant kinematic pattern potentially serving as a key contributor. The study underscores the importance of understanding intersegmental coordination for managing foot stiffness, which could have implications for improving gait mechanics and preventing injuries. Further research is needed to explore how these findings can be applied to individuals with various foot conditions or pathologies.