Effect of Walking Speed and Adding a Backpack on Trunk Dynamics During Treadmill Walking

摘要

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, twelve subjects walked on a level treadmill at a range of walking speeds (0.6 m/s - 1.6 m/s) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking load carriage decreases transverse pelvic and thoracic rotation, the mean relative phase between pelvic and thoracic rotations, and increases hip excursion. In addition, it was hypothesized that these changes would coincide with a decreased stride length and increase stride frequency. The findings supported the hypotheses. It was additionally hypothesized that the increased MOI of the upper body caused by the added mass of the backpack would result in an increase in upper body torque, an increase in lower body torque, and an increase in net body torque. Higher levels of upper body torque were observed in the backpack condition compared to the no backpack condition. However, the increase in upper body torque was 225%, while upper body MOI increased by 400%. In contrast to our hypothesis, decreased lower body torque was also observed in the backpack condition compared to the no backpack condition Dimensionless analyses indicated that there was a significantly larger contribution of hip excursion and smaller contribution on transverse plane pelvic rotation to increases in stride length during load carriage. In addition, there was a significant effect of load carriage on the amplitudes of transverse pelvic and thoracic rotation and the relative phase of pelvic and thoracic rotation. It was concluded that the shorter stride length and higher stride frequency observed when carrying a backpack is the result of decreased pelvic rotation. The shorter stride length and higher stride frequency observed during load carriage are associated with changes in transverse plane kinematics.