Effect of Fatigue on Movement Patterns During a Loaded Ruck March.

INTRODUCTION: Loaded ruck marching is a common training and operational task for many members of the military. It is known to cause fatigue, affect soldier readiness, and can lead to traumatic and overuse injuries. Quantifying the gait changes that occur over the course of a loaded ruck march may provide a better understanding of injury mechanisms and potentially allow for development of individualized injury-prevention training programs. This study examined the change in soldiers' gait patterns over the course of a loaded ruck march in order to examine the correlation between fatigue and kinematic parameters. Fatigue is a subjective term that may encompass factors such as energy expenditure, muscle exhaustion, and cognitive engagement. Since it can be difficult to quantify, the current study makes the broad assumption that fatigue increases in some (potentially nonlinear) fashion during a loaded ruck march.

METHOD: Three platoons of soldiers participated in a field training exercise with inertial measurement sensors placed on their chests and ankles to record gait parameters throughout a 7-mile ruck march. The effects of fatigue on stride length, stride width, ankle yaw, and torso lean (anterior-posterior [AP] and side-to-side [SS]) were compared using one-way repeated measure analyses of variance.

RESULTS: In comparing the first and last quarters of the ruck march, stride length decreased, stride width increased, stride width variability increased, AP torso lean variability increased, and SS torso lean variability increased.

CONCLUSION: Although they do not describe a direct relationship to injury, these results can inform enhanced approaches to quantify and predict soldier fatigue and more reliably prevent future injury.