The Effect of Step Length on Vertical and Posterior Components of Ground Reaction Force and Loading Rate During Fixed-Cadence Marching: Implications for Lower Extremity Stress Fracture in Military

Stress fracture occur following bone exposure to cyclic sub-threshold loadings before repairing previous micro-fractures. The aims of this study were: 1) to assess and compare the ground reaction force and loading rate responses of the fixed-cadence marching at the fourth step and single-leg landing; and 2) the effect of over striding in the fourth step of fixed-cadence marching on the ground reaction forces and loading rates. a total of ten male students of Police (NAJA) University were enrolled. Five experiments including two single leg landing، two fixed-cadences marching، and regular running experiments were applied. The experiments data were collected with 200 Hertz using a force plate device. The results showed a high correlation between the fixed-cadence marching at the fourth step and single leg landing with both studied step lengths for the peak vertical and posterior components of ground reaction force and loading rate (r = 0. 863، r = 0. 781، r = 0. 847، and r = 0. 798 for step length of 25 centimeter، and r=0. 865، r=0. 74، r=0. 831، and r=0. 716 for step length of 50 centimeter; p <0. 05). By increasing the step length، all variables increased significantly (p <0. 05). The increase in the amount and rate of ground reaction forces can increase the risk of stress fracture on the lower extremities of soldiers and officers. As a mechanism to prevent over striding and consequently stress fractures in the fixed-cadence marching، it is suggested that recruits with the same height can be arranged to a group during marching، so that their step length maintain around their preferred one.