Can Asymmetrical Mechanical Loading Be Accurately Inferred From the Analysis of Skeletal Material?

Reconstructing habitual limb preference in the past is crucial for understanding the evolution of hominin behavior. However, our ability to reliably identify asymmetrical behaviors from bone remains is limited due to a lack of experimental evidence directly correlating a history of loading asymmetry with skeletal asymmetry. We address this gap by analyzing an existing laboratory sample of rats subjected to asymmetric loading, relying on four methodological approaches that address both external and internal bone morphology.

Data were derived from nine genetically consistent Wistar rat tibiofibulae, exposed to controlled asymmetrical loading. Asymmetry was evaluated using 3D geometric morphometrics for analyzing bone shape, cross-sectional geometry for assessing biomechanical strength, cortical thickness mapping of compact bone distribution, and V.E.R.A. (1.0 and 2.0) for quantifying 3D muscle attachment sites.

The findings revealed a clear association between asymmetrical loading and bone asymmetry, particularly in the distal periosteum and medio-anterior midshaft, which exhibited notable 3D shape changes and increased cortical thickness. Additionally, polar second moment of area values were higher in stimulated limbs, indicating improved biomechanical function. The 3D entheseal areas of the stimulated limbs were also proportionally larger, with no apparent association with allometric factors.

This study provides experimental proof-of-concept that asymmetric biomechanical loading influences skeletal bilateral asymmetry, suggesting that reconstructing limb preference is feasible using these methods. Future applications could enhance our understanding of the evolution of hominin handedness and its role in ancient lifeways.