The Effects of Load Carriage and Muscle Fatigue on Lower-Extremity Joint Mechanics

Military personnel are commonly afflicted by lower-extremity overuse injuries. Load carriage and muscular fatigue are major stressors during military basic training. Purpose: To examine effects of load carriage and muscular fatigue on lower-extremity joint mechanics during walking. Method: Eighteen men performed the following tasks: unloaded walking, walking with a 32-kg load, fatigued walking with a 32-kg load, and fatigued walking. After the second walking task, muscle fatigue was elicited through a fatiguing protocol consisting of metered step-ups and heel raises with a 16-kg load. Each walking task was performed at 1.67 m·s^− 1 for 5 min. Walking movement was tracked by a VICON motion capture system at 120 Hz. Ground reaction forces were collected by a tandem force instrumented treadmill (AMTI) at 2,400 Hz. Lower-extremity joint mechanics were calculated in Visual 3D. Results: There was no interaction between load carriage and fatigue on lower-extremity joint mechanics (p>.05). Both load carriage and fatigue led to pronounced alterations of lower-extremity joint mechanics (p < .05). Load carriage resulted in increases of pelvis anterior tilt, hip and knee flexion at heel contact, and increases of hip, knee, and ankle joint moments and powers during weight acceptance. Muscle fatigue led to decreases of ankle dorsiflexion at heel contact, dorsiflexor moment, and joint power at weight acceptance. In addition, muscle fatigue increased demand for hip extensor moment and power at weight acceptance. Conclusion: Statistically significant changes in lower-extremity joint mechanics during loaded and fatigued walking may expose military personnel to increased risk for overuse injuries.

Keywords:

• gait
• joint loading
• kinetics

Acknowledgments

We thank Cara Reedstrom, Michael Lawrence, Barbara Schornstein, and Jonathan Hill for their assistance in data collection. Funding was provided by the Department of the Army (Grant No. W81XWH-08-1-0587).