Kinematic coupling relationships exist between non-adjacent segments of the foot and ankle of healthy subjects

Pathologies of foot and ankle structures affect the kinematics at the site of the impaired structure but also influence kinematics elsewhere in the foot and ankle. An understanding of kinematic coupling relationships in the foot could provide insight into mechanisms that explain differences in foot and ankle kinematics between healthy and pathological subjects. The aim of this study was to explore foot and ankle kinematic coupling relationships between adjacent and non-adjacent segments of healthy subjects and evaluate individual variability of and effect of walking speed on these relationships.Gait of 14 subjects was recorded at comfortable and two slower walking speeds to assess individual foot kinematics during stance phase. A qualitative evaluation of the coupling relationships was made using angle-angle plots to determine their consistency, i.e. changes in movement direction of each segment occurred at the same time and the plot returned along the same line after the turning point. The Pearson correlation coefficient of determination (R2) was used to provide a quantitative evaluation of coupling. Individual variability was assessed with the coefficient of variation (CV). The Friedman-test was used to test the effect of walking speed.Consistent coupling relationships were observed between hindfoot in/eversion and hallux plantar/dorsiflexion (R2 0.7, CV 0.2), between hindfoot in/eversion and forefoot ab/adduction (R2 0.5, CV 0.3) and between leg rotation and midfoot collapse/elevation (R2 0.5, CV 0.4). Less or non-consistent coupling relationships were observed between the other studied segments. Walking speed significantly influenced coupling relationships between hindfoot and midfoot.

► Kinematic coupling of foot and ankle segments during walking was studied. ► Coupling exists between adjacent and non-adjacent segments. ► Hindfoot inversion was strongly related to hallux dorsiflexion and forefoot adduction. ► Leg rotation was related to medial arch collapse. ► Walking speed only influenced the kinematic coupling between hindfoot and midfoot.