Effect of exertion on the biomechanics of walking with load carriage and running in young, healthy women.

Musculoskeletal injuries, a major impediment to medical military readiness, are often associated with muscle fatigue caused by prolonged, repeated activities, including running and walking with load carriage. Here, we investigated the biomechanics of women running without a load and walking with load carriage to identify kinetic and kinematic parameters affected by exertion-related changes under both conditions. We collected motion-capture data and computed tomography images from 20 young, healthy women running without a load for 5 km at a subject-specific pace and walking with a 22.7-kg load for 5 km at a speed of 1.5 m/s. We developed individualized musculoskeletal models for each condition and characterized changes in kinetic and kinematic parameters for each subject between the start (0 km) and end of each 5-km session. We found that peak trunk flexion angle increased for both conditions (effect size ≥ 0.80), with the same trend for 18 of the 20 subjects. Peak hip extension, ankle dorsiflexion, and subtalar inversion internal moments had the same directional changes in both conditions, although not always meeting the significance threshold adjusted for multiple comparisons or yielding an effect size ≥ 0.80. In conclusion, this exploratory study identified exertional effects in women running without a load or walking with load carriage that resulted in biomechanical gait changes in the same direction, which could be used to develop countermeasures to reduce the risk of musculoskeletal injury.