Context: Obesity is a growing global health concern. The increased body mass and altered mass distribution associated with obesity may be related to increases in plantar shear that putatively leads to physical functional deficits. Therefore, measurement of plantar shear may provide unique insights on the effects of body mass and body distribution on physical function or performance. Purpose: 1) To investigate the effects of body mass and distribution on plantar shear; 2) To examine how altered plantar shear influences postural control and gait kinetics. Hypothesis: 1) a weighted vest forward distributed (FV) would shift the center of pressure (CoP) location forward during standing compared with a weighted vest evenly distributed (EV); 2) FV would increase plantar shear spreading forces more than EV during standing; 3) FV would increase postural sway during standing while EV would not; and 4) FV would increase peak braking force, plantar impulses, and plantar shear spreading forces during walking more than EV. Methods: Twenty healthy young males participated in four different tests: 1) static test (for measuring plantar shear and CoP location without acceleration; 2) two-leg standing postural control test; 3) one-leg standing postural test; and 4) walking test. All tests were executed in three different weight conditions: 1) unweighted (NV); 2) evenly distributed vest (EV) with 20% added body mass; and 3) front-loaded vest (FV), also with 20% added body mass. Plantar shear stresses were measured using a pressure/shear device, and several shear and postural control metrics were extracted. Repeated measures ANOVAs with Holms post hoc test were used to compare each metric among the three conditions (α = 0.05). Results: FV and EV increased both anterior-posterior and medial-lateral plantar shear forces in single-foot trials compared to NV. FV shifted CoP forward. FV and EV showed decreased CoP range and velocity and increased time-to-boundary (TTB) during postural control compared to NV. While EV increased medial-lateral plantar shear spreading force, FV increased anterior-posterior plantar shear spreading force during walking. Conclusion: Added body mass increases plantar shear spreading forces. Body mass distribution had greater effects during dynamic tasks. In addition, healthy young individuals seem to quickly adapt to external stimuli to control postural stability. However, the interactive effects between body mass and distribution may disrupt physical function and/or performance in other populations—such as elderly, obese, and diabetes. Plantar shear may play a critical role in clinical diagnosis. However, as it is the first step study, follow-up studies are necessary to further support the clinical role of plantar shear.



College and Department

Life Sciences



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evenly distributed weighted vest, front-loaded weighted vest, plantar shear spreading force



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Life Sciences Commons