The Relationship between Body Mass Index and Long Bone Morphology: A Multidirectional Analysis

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Title: The Relationship between Body Mass Index and Long Bone Morphology: A Multidirectional Analysis
Author: Agostini, Gina Marie
Advisors: Ann H. Ross, Committee Chair
D. Troy Case, Committee Member
Scott M. Fitzpatrick, Committee Member
Abstract: Obesity has increased significantly during the last three decades in all ages and both sexes among European and African Americans, and Hispanic individuals of Mexican origin. Biomechanical literature is replete with evidence of compensatory adaptations made by overweight individuals to cope with adiposity in daily life, yet aside from correlations between weight and arthritis frequencies, little attention has been paid to the effect that obesity has on the human skeleton. Because a key goal of physical anthropology is to create a thorough and accurate biological profile of individuals being analyzed, more research is needed to investigate implications of obesity, a condition which clearly affected how an individual appeared in life. The goal of this project was two fold: [1] to assess diaphyseal cross-sectional geometry of both humerii, the left femur and the left tibia and [2] to test whether the expression of musculoskeletal stress markers (MSMs) of each bone were affected by weight. Both properties have been shown to be influenced by load and mechanical action resulting from stress-induced remodeling responses at the cellular level. A sample of modern males of European ancestry was utilized for this research. After controlling for age, multivariate statistics show significant (p-value < 0.05) elongation of the mediolateral dimension of the proximal and midshaft femur in overweight individuals. T-tests show that overweight individuals have significantly large ML dimensions in this region (p-value < 0.05), suggesting that femora of overweight individuals undergo abnormally high rates of sagittal stress. These findings correlate well with biomechanical gait analyses, which show that overweight individuals display significant increases in step width and hip abduction, disproportionately large mediolateral ground reaction forces, and longer periods of stance during the walking cycle when compared to normal weight controls. All of these activities, especially when coupled with movement of excess mass, could explain abnormal sagittal stress of the proximal femur. A significant bilateral effect of BMI on the ML dimension of the proximal humeru was also found (p-value < 0.01) after controlling for age. T-tests confirmed that overweight individuals have significantly large dimension in this region (p-value < 0.05), perhaps due to high loads transmitted through the shoulder when an individual uses his arms to rise from a seated position. Despite their success in archaeological assessments of activity, MSMs were not found to be a suitable method of differentiating overweight individuals from normal or underweight individuals. This could be due to biological defense mechanisms at sites of muscle attachment for coping with high routine stresses, genetic influences on MSM expression, presence of both overweight and heavily-muscled individuals in the overweight category, or lack of significant activity differences between overweight and normal or underweight individuals.
Date: 2009-04-20
Degree: MA
Discipline: Anthropology

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