Influence of fatigue and load carriage on mechanical loading during walking.

Load carriage and muscular fatigue are two major stressors experienced by military recruits during basic training. The purpose of this study was to assess the influences of load carriage and muscular fatigue on ground reaction forces and ground reaction loading rates during walking. Eighteen healthy males performed the following tasks in order: unloaded and unfatigued walking, loaded and unfatigued walking, fatiguing exercise, loaded and fatigued walking, and unloaded and fatigued walking. The fatiguing exercise consisted of a series of metered step-ups and heel raises with a 16-kg rucksack. Loaded walking tasks were performed with a 32-kg rucksack. Two-way repeated measures analysis of variances were used to determine the effects of fatigue and load carriage on ground reaction forces and loading rates. Muscular fatigue has a significant influence on peak vertical ground reaction force and loading rate (p < 0.01). Load carriage has a significant influence on peak ground reaction forces and loading rates (p < 0.001). As both muscular fatigue and load carriage lead to large increases of ground reaction forces and loading rates, the high incidence of lower extremity overuse injuries in the military may be associated with muscular fatigue and load carriage.