The effect of body weight support on squat biomechanics
To yield insights into how assistive technology can impact basic human motion, here we investigate the effects of varied body weight support on the biomechanics of human subjects rising from a squatted position. This rising motion occurs when individuals rise from a seated squat, rise from a chair, or lift up an object, and may occur as a component of other motions as well. To study the effect of weight support on this motion we designed an apparatus that utilizes controlled pneumatic actuators allowing for variable load profiles on either side of the body. In this experiment, a sinusoidal vertical load was applied at the hips during the rising phase of the squatting motion. Two levels of load supported motions, 20% BW and 35% BW, were compared to unsupported squats. There were statistically significant differences in the joint moments and forces when squatting with BW support versus squatting without, based on the results of two-way, repeated measures ANOVA (p < 0.01). Presented as mean ± SD, peak knee moments decreased from 4.725 ± 0.747 (%BW*height) without support, at the beginning of the squat, to 3.660 ± 1.010 (%BW*height) with 35% BW support. Peak hip moments declined from 3.433 ± 0.755 (%BW*height) without support, at the beginning of the squat, to 2.627 ± 0.815 (%BW*height) at 35% BW support. We developed a simplified dynamic model of the squatting motion that predicts and explains these changes. However, despite the overall agreement with our model, the assistive load support also induced kinematic adaptations in the subjects that were not predicted by the model. Subjects tended to maintain a relatively high trunk tilt under the influence of load support until nearing the end of the squat, causing the actual forces, moments, and CoP to deviate from the predicted values during this final phase of the squat.^
Justin Seipel, Purdue University.
Biomedical engineering|Mechanical engineering|Biomechanics
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