External frontal plane loads may be associated with tibial stress fracture.

PURPOSE The role of applied external loads in tibial stress fracture is poorly understood. The purpose of this study was to determine whether the magnitude and angle of frontal and sagittal force vectors and the magnitude of the free moment of ground reaction force (the torsional moment between the foot and the ground) during running gait differ between military recruits with and without a history of tibial stress fracture. METHODS Ten male military recruits with tibial stress fracture history and 20 matched controls performed shod running trials over a force plate. The magnitude and the direction of the frontal and sagittal plane ground reaction force, in addition to the free moment, were compared between the groups. RESULTS The frontal plane force vector was directed significantly more medially in the stress fracture group during midstance and late stance (P < 0.05). The magnitude of frontal and sagittal plane ground reaction forces and the free moment were not higher in the stress fracture group compared with controls. CONCLUSION These data highlight differences in the direction with which external forces in the frontal plane are applied in military recruits with a history of tibial stress fracture. These differences may be important in the development of the injury.

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