Locomotor variation and bending regimes of capuchin limb bones
Article first published online: 10 FEB 2009
Copyright © 2009 Wiley-Liss, Inc.
American Journal of Physical Anthropology
Volume 139, Issue 4, pages 558–571, August 2009
How to Cite
Demes, B. and Carlson, K. J. (2009), Locomotor variation and bending regimes of capuchin limb bones. Am. J. Phys. Anthropol., 139: 558–571. doi: 10.1002/ajpa.21020
- Issue published online: 7 JUL 2009
- Article first published online: 10 FEB 2009
- Manuscript Accepted: 15 DEC 2008
- Manuscript Received: 19 JUL 2008
- National Science Foundation. Grant Number: NSF BCS 0548892
- limb bone loading;
- substrate reaction force;
- 3D kinematics
Primates are very versatile in their modes of progression, yet laboratory studies typically capture only a small segment of this variation. In vivo bone strain studies in particular have been commonly constrained to linear locomotion on flat substrates, conveying the potentially biased impression of stereotypic long bone loading patterns. We here present substrate reaction forces (SRF) and limb postures for capuchin monkeys moving on a flat substrate (“terrestrial”), on an elevated pole (“arboreal”), and performing turns. The angle between the SRF vector and longitudinal axes of the forearm or leg is taken as a proxy for the bending moment experienced by these limb segments. In both frontal and sagittal planes, SRF vectors and distal limb segments are not aligned, but form discrepant angles; that is, forces act on lever arms and exert bending moments. The positions of the SRF vectors suggest bending around oblique axes of these limb segments. Overall, the leg is exposed to greater moments than the forearm. Simulated arboreal locomotion and turns introduce variation in the discrepancy angles, thus confirming that expanding the range of locomotor behaviors studied will reveal variation in long bone loading patterns that is likely characteristic of natural locomotor repertoires. “Arboreal” locomotion, even on a linear noncompliant branch, is characterized by greater variability of force directions and discrepancy angles than “terrestrial” locomotion (significant for the forearm only), partially confirming the notion that life in trees is associated with greater variation in long bone loading. Directional changes broaden the range of external bending moments even further. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc.