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

Biomechanics of spear throwing, with implications for fossil hominins


Anthropology, Washington University in Saint Louis

Saturday 3:45-4:00, Galleria North Add to calendar

The degree to which skeletal measures available in the fossil record translate to observable differences in performance in living subjects is of primary importance to functional morphologists. Here the biomechanical effects of body proportions and effective mechanical advantage (EMA) on spear throwing are explored. Kinematic data were collected for 41 subjects throwing a spear-like object, from which joint angular velocities (ω) and linear kinetic energy (Ke) were calculated. Isometric arm strength was assessed with a compression/tension load cell, and EMA and muscle dimensions in the arm were measured using MRI. It was hypothesized that spear Ke would be predicted by body proportions, as well as arm strength and EMA (through their effect on joint angular velocity).

As predicted, EMA and triceps size together explained 48% of the variation in elbow extension ω. However, contrary to predictions, elbow extension ω was not found to be a significant predictor of spear Ke once shoulder Ke was taken into consideration. Shoulder Ke explains 80% of the variation in spear Ke, indicating that the overwhelming majority of the energy provided to the spear is a result of body motion. No aspects of arm anatomy measured significantly explain the residual variation in spear Ke. Furthermore, arm strength is correlated with shoulder Ke, indicating a correlation between arm strength and overall body strength that largely explains throwing performance, while skeletal measurements provide little additional information. This strongly suggests caution should be taken when attempting to infer specific functions from the fossil record without experimental evidence.

This project was funded by a grant from the Society for Integrative and Comparative Biology, grant number 1033-80310 PDS 110181, and the Graduate School at Washington Univerisity in Saint Louis.

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