The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Functional Morphology and Variation: The Effects of Obesity on the Cross-Sectional Geometry of the Humerus


Behavioral Sciences, University of Michigan-Dearborn

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Research using a functional morphology approach to address the effects of obesity on the human skeleton has had success with the load bearing bones of the lower limb. The upper limb, however, can play a significant role in sit-to-stand locomotion in obese subjects and could prove useful for the estimation of body mass from the skeleton. Focusing now on the humerus, this research continues previous work on the cross-sectional shape of the long bones, work that was originally encouraged and supervised by Richard Jantz. With increased compressive forces acting on the humerus in sit-to-stand locomotion, the current hypothesis is that the cross-sectional area will be greater in obese subjects compared to normal or underweight subjects. The sample consists of known individuals from the Bass Donated Skeletal Collection (n=40). Cross-sectional area of the humerus was calculated at three locations along the diaphysis. When comparing the cross-sectional area of the midshaft of obese individuals (BMI>30) to non-obese individuals (BMI<30) using a stepwise regression, the ANOVA yielded insignificantly low correlations for both males (R-squared=0.037) and females (R-squared=0.036) at all locations. The male humeral cross-sections were significantly larger than the females, with sex having the greatest correlation with cross-sectional area (R-squared=0.568). Thus, the results of this preliminary study do not warrant rejection of the null hypothesis. Though the signal is stronger for sexual dimorphism, changes in locomotion due to obesity inevitably affect the cross-sectional geometry of the long bones, but more so in the lower limb than in the humerus.

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