Establishment of the simplified technique for estimating joint moments in foot during running

Abstract

To prevent injuries such as stress fractures during long-distance running, it is important to clarify the joint loads on the foot. The purpose of this study was to establish a method of estimating joint moments on foot during stance phase in running. Loads on the ankle, tarsometatarsal, and metatarsophalangeal joints were estimated by a new simplified foot model with the three-dimensional force distribution on the bottom of shoe sole. Three-dimensional ground reaction force distributions were obtained from a running test with special shoes on which three-axis miniature force sensors had been mounted. Foot model consisted of three segments: toe, mid foot, and heel. Each segment was linked with metatarsophalangeal, tarsometatarsal, and ankle joints, respectively. By calculating inverse dynamics with this model, each joint moment component, which is the contribution of forces on each sensor to joint moments, could be estimated. Each joint moment was equivalent with the sum of moment components. Results showed that the tarsometatarsal and metatarsophalangeal joint moments are estimated during the whole stance phase. The moment component distributions of each joint could also be quantified. In comparison of the moment components corresponding to each metatarsal bone, the loads of the second- and third-ray metatarsal bones were higher than those of the others. Furthermore, the effect of sole thickness distribution on moment component distribution was also confirmed. Increase of sole thickness in the vicinity of the first and fifth metatarsal bone heads reduced the load of the second- and third-ray metatarsal bones. These results showed a possibility to prevent stress fractures on foot with the sole design.