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

Electromyography of chimpanzee mastication: muscle recruitment order


Department of Organismal Biology and Anatomy, The University of Chicago

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This study investigated patterns of muscle recruitment of both the balancing- and working-side muscles during mastication in Pan troglodytes. Video data of left- and right-side chewing of a variety of foods was taken from four individuals, and the corresponding electromyographic data of the firing of the superficial and deep masseter and the anterior and posterior temporalis muscles were collected. Results were compared to jaw-muscle recruitment order in Old World monkeys. EMG data were processed using a root-mean-square analysis with a time constant of 84 milliseconds. For each power stroke, for each muscle, we calculated the relative timing of peak activity and of 25%, 50%, 75% activity before and after the peak. This analysis revealed that, for both the superficial and the deep masseter muscles, peak firing of the balancing-side muscle precedes that of the working side. For the anterior temporalis, peak firing of the balancing side precedes that of the working side. The working- and balancing-side posterior temporalis muscles show no consistent firing pattern. These patterns are consistent with those of Old World monkeys for the superficial masseter, but differ for the deep masseter and posterior temporalis.

Funded by NSF (BCS 725147)

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