Abstract
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. 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. 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 elicit greater compensatory changes during walking than EV. Twenty healthy young males participated in four different tests: 1) static test (for measuring plantar shear and CoP location without acceleration, 2) bilateral-foot standing postural control test, 3) single-foot standing postural test, and 4) walking test. All tests were executed in three different weight conditions: 1) unweighted (NV), 2) EV with 20% added body mass, and 3) 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). FV and EV increased both AP and ML plantar shear forces compared to NV. FV shifted CoP forward in single-foot trials. FV and EV showed decreased CoP range and velocity and increased Time-to-Boundary (TTB) during postural control compared to NV. EV and FV showed increased breaking impulse and propulsive impulse compared to NV. In addition, EV showed even greater impulses than FV. While EV increased ML plantar shear spreading force, FV increased AP plantar shear spreading force during walking. 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, as this is a first step study, follow-up studies are necessary to further support the clinical role of plantar shear in other populations such as elderly and individuals with obesity or diabetes.
Highlights
Increased body mass inherently causes greater loading under the plantar surface of the foot during weight-bearing activity [1,2,3] Complications such as balance issues, falls and lower extremity injuries [4,5,6] in the obese population may be related to the altered biomechanics and plantar loading that arises from a chronically increased body mass
front-loaded weighted vest (FV) and evenly distributed weighted vest (EV) increased both AP and ML plantar shear forces compared to NV
FV and EV showed decreased CoP range and velocity and increased Time-to-Boundary (TTB) during postural control compared to NV
Summary
Increased body mass inherently causes greater loading under the plantar surface of the foot during weight-bearing activity [1,2,3] Complications such as balance issues, falls and lower extremity injuries [4,5,6] in the obese population may be related to the altered biomechanics and plantar loading that arises from a chronically increased body mass. Obesity typically positions the whole body center of mass (CoM) further anterior, altering loading distributions This altered loading likely has a direct influence on obesity related complications such as postural instability [7] and increased fall risk [4], increased lower extremity muscle activity [8], altered gait mechanics [9], and reduced plantar cutaneous mechanoreceptor sensitivity [10]. No studies have used added body mass to simulate the forward mass distribution that occurs with obesity
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