Primary factors affecting maximum torsional loading of the tibia in running.

The purpose of this study was to determine primary factors that contribute to the magnitude of the maximum torsional moment on the tibia during running based on information from three-dimensional shank kinematics and ground reaction forces. Eight male subjects were asked to run along a straight track at 5.0 m s-1. Data were collected using two high-speed cameras and a force platform. Each subject's left foot and tibia were modelled as a system of coupled rigid bodies. First, net axial moments acting at both ends of the tibia were calculated using inverse dynamics. Then the tibial torsional moment was determined from the quasi-equilibrium balance of the net tibial axial moments. Our results showed considerable inter-individual variations for the tibial torsional moment during the stance phase of running. The maximum torsional moment reflecting external rotational loading of the proximal tibia was significantly correlated with the outward tilt angle of the shank in the frontal plane (r = 0.78, p < 0.05) and with the vertical force of ground reaction (r = 0.70, p < 0.05). In conclusion, lowering tibial torsional loading by interventions based on the present findings may lead to the reduction of running injuries that occur in athletes' tibiae.