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Lower extremity biomechanical changes associated with symmetrical torso loading during simulated marching.

The dose-response relationship between biomechanical variables and the magnitude of external loads is unclear. The use of different load distributions (e.g., pack types) may confound results because of changes in torso center of mass. Therefore, we examined the relationship between load magnitude and sagittal plane lower extremity mechanics of Soldiers walking with two symmetrically distributed loads. Fourteen Soldiers marched on a force-sensing treadmill at 1.34 m/s for 10 minutes with no load (BW_00) and while wearing vest-borne loads of 15 kg (BW_15) and 55 kg (BW_55). The effects of the loads on sagittal plane joint angles and moments were compared using 1-way repeated measures analyses of variance. Compared with BW_00, knee extension moment increased with the 15- and the 55-kg loads (both p < 0.003), confirming previously reported load-related biomechanical responses. Knee moment increases during early stance appeared to be the primary means by which the lower extremity counteracted BW_15 during early stance; in contrast, hip extensors and ankle dorsiflexors appeared to be the primary muscular efforts responsible for propulsion during late stance. Findings elucidated the effects of load magnitude on lower extremity mechanics without postural changes that result from pack-related shifts in torso center of mass.