Changes in Kinematic Coupling Among the Rearfoot, Midfoot, and Forefoot Segments During Running and Walking.

BACKGROUND: Understanding the concept of kinematic coupling is essential when selecting the appropriate therapeutic strategy and grasping mechanisms for the occurrence of injuries. A previous study reported that kinematic coupling between the rearfoot and shank during running and walking were different. However, because foot mobility involves not only the rearfoot but also the midfoot or forefoot, kinematic coupling is likely to occur among the rearfoot, midfoot, and forefoot segments. We investigated changes in kinematic coupling among the rearfoot, midfoot, and forefoot segments during running and walking.

METHODS: Ten healthy young men were instructed to run (2.5 ms-1 ) and walk (1.3 ms-1 ) on a treadmill at speeds set by the examiner. The three-dimensional joint angles of the rearfoot, midfoot, and forefoot were calculated based on the Leardini foot model Kinematic coupling was evaluated with the absolute value of the cross-correlation coefficients and coupling angles obtained by using a vector coding technique.

RESULTS: The cross-correlation coefficient between rearfoot eversion/inversion and midfoot dorsiflexion/plantarflexion was significantly higher during running ( r = 0.79) than during walking ( r = 0.58), suggesting that running requires stronger kinematic coupling between rearfoot eversion/inversion and midfoot plantarflexion/dorsiflexion than walking. Furthermore, the coupling angle between midfoot eversion/inversion and forefoot eversion/inversion was significantly less during running (30.0°) than during walking (40.7°) ( P < .05). Hence, the magnitude of midfoot frontal plane excursion during running was greater than that during walking.

CONCLUSIONS: Excessive rearfoot eversion during running is likely to lead to excessive midfoot dorsiflexion, and such abnormal kinematic coupling between the rearfoot and midfoot may be associated with mechanisms for the occurrence of injuries.