The effects of mobility and physical activity on human postcranial skeletal variation

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Modern humans have relatively lightly built skeletons compared to other primates and earlier human populations, a condition that may predispose modern humans to bone-related health risks such as osteopenia and osteoporosis. Reduced physical activity levels as well as dietary changes, especially following the adoption of agriculture, have been put forth as major contributing factors driving these reductions in human bone mass over the last 10,000 years. This collaborative project will assess variation in bone structure in a large human skeletal sample encompassing a diversity of regional populations and subsistence strategies to evaluate the effects of physical activity levels, diet, and other factors on the modern human skeleton. Investigating the human skeleton from past and recent populations, as well as integrating studies of living athletes, will effectively frame the extent of normal variation in modern humans. A better understanding of skeletal variability will, in turn, produce insight into the factors that contribute to contemporary bone health and related costly medical conditions, such as osteopenia and osteoporosis. This project will provide educational and training opportunities to undergraduate and graduate students, including women and minorities, postdoctoral training for young professionals, and educational enrichment opportunities for K-12 educators from rural and urban school districts in Pennsylvania. The data collected and the educational modules developed during the course of this project will be made available to other researchers, educators, and the general public through the online data repositories. This study tests the hypothesis that trabecular and cortical bone structure in limb elements reflects mobility and activity differences between human populations, implicating an increasingly sedentary lifestyle as the major factor driving the apparent decrease in skeletal mass in recent humans. Recent work has suggested that highly mobile groups, like hunter-gatherers, have significantly more robust skeletons compared to sedentary agriculturalists and more recent contemporary populations. Reductions in mobility and physical activity, which have purportedly coincided with the adoption of agriculture and subsequent technological advances, have been argued to be critical factors driving the reduction in skeletal mass in recent humans. This study will characterize variation in both trabecular and cortical bone across a large number of human populations and evaluate this range of variation in relation to differences in physical activity, mobility, body size, diet, and ancestry. The study design consists of two major components. Microcomputed tomography scan data will be collected from a diverse skeletal sample of recent humans to assess variation in trabecular and cortical bone structure in multiple postcranial elements (humerus, femur, tibia, cervical vertebra). This skeletal sample will include representatives of groups practicing various subsistence and technological strategies such as foragers, horticulturalists, intensive agriculturalists, and post-industrial populations drawn from multiple locations globally. In addition, peripheral quantitative computed tomography (pQCT) scan data will be collected from living elite athletes and non-athlete controls to assess the effects of lifelong intensive physical activity on skeletal mass. Comparisons between the two components of the study will inform understanding of activity and behavior related changes in human skeletal mass through time.