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

Scaling of forearm muscle architecture in primates


1Department of Biology, Pennsylvania State University Altoona, 2Department of Evolutionary Anthropology, Duke University, 3Institute for Human Evolution, University of the Witwatersrand

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The bony morphology of the distal humerus has been demonstrated to correlate with locomotor behavior. These osteological differences are thought to reflect variation in the force production capabilities of the forearm musculature, necessitated by differences in substrate interaction between locomotor groups. Muscle strength may be affected by muscle mass, muscle fiber architecture, and mechanical advantage. Previously, we demonstrated that primate forearm muscle mass scales isometrically with body mass. Here, we examine the potential relationship between locomotion and muscle fiber architecture, including physiological crossectional area (PCSA) and fascicle length (FL), of the forearm musculature.

The sample includes six strepsirrhines, six platyrrhines and seven catarrhines. We measured wet mass (MM), linear dimensions, and FL for each antebrachial muscle following dissection. PCSA was calculated for each muscle and studied across muscles groups (flexors, extensors, and “others”) using RMA regression (alpha = 0.05). Total forearm (TFor) PCSA is tightly correlated with TFor MM across the whole sample and within each suborder and is slightly positively allometric across the whole sample and within strepsirrhines and catarrhines (but not platyrrhines). Similar correlations and allometry between MM and PCSA are found within the flexor and extensor compartments. FL is not highly correlated with total MM variables and appears instead to relate to locomotor patterns. Thus primate forearm muscles have relatively consistent (though slightly positively allometric) crossections, but vary according to FL, suggesting locomotor adaptations in stretch and flexibility, but not force production. Therefore variation in epicondylar anatomy instead likely relates to adaptations for mechanical advantage.

This work was funded by Pennsylvania State University

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