The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

What can muscle insertions tell us about activity during life? Functional anatomy and development of the deltoid tuberosity in wild-type mice


1Department of Anthropology, University of Toronto, 2Department of Anatomy, Midwestern University, 3Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 4Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC

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Muscle attachment sites are often used to reconstruct the lifestyles and activity patterns of past populations, but little is known about how activity patterns influence the development of muscles and the morphology of their bone insertions. The main goal of this project was to explore this relationship by testing how activity influenced the morphological development of the deltoids and pectoralis muscles and the corresponding deltoid tuberosity in wild-type mice subjected to three experimental activity patterns: sedentary-control, activity-wheel running, and activity-climbing. Each mouse (four- and seven-week-old at the start) received three vital fluorescent bone-labeling dyes (alizarin, DCAF, xylenol) at two-week intervals over an eleven-week period to allow for histological examination and calculation of bone growth rates underlying the deltoid attachment site. After the experiment, the muscles were weighted, fiber and sarcomere lengths were calculated and humeri were cleaned, digitally photographed, and 100-micron thick cross-sections at the deltoid tuberosity were prepared for histological analysis. Analysis of sarcomere length and muscle weight indicate that wheel-running mice had greater overall excursion, especially in the pectoralis muscles, while the climbing mice had greater deltoid muscle stretch advantage compared with the sedentary mice. The rate of bone growth was significantly greater in wheel-running mice than the other groups. However, the climbing mice showed more histologic variation in bone growth remodeling (e.g. evidence of drifting osteons). Results contribute to a better understanding of how muscle and bone interact throughout their development and improve our ability to interpret behavior from human and non-human primate skeletal remains.

This study was funded by Wenner-Gren Foundation Dissertation Fieldwork Grants to KR and DG, NSF Doctoral Dissertation Improvement Grant BCS-0824552, NSF DGE-0801634, and GW Academic Excellence funding to the Center for the Advanced Study of Hominid Paleobiology.

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