Abstract
ObjectivesWe sought to determine the relationships between muscle size, function, and polar second moments of area (J) at the midshaft femur, proximal tibia, and midshaft tibia.Materials and MethodsWe used peripheral quantitative computed tomography to quantify right femoral and tibial J and soft tissue cross‐sectional areas, and force plate mechanography to quantify peak power output and maximum force of the right limb, among athletic women and control subjects.ResultsLower limb bone J exhibited strong relationships with estimated force but not power between both groups. Among controls, the strongest relationships between force and J were found at the midshaft femur. Among athletes, these relationships shifted to the tibia, regardless of body size, likely reflecting functional strain related to the major knee extensors and ankle plantarflexors. Together, muscle force and stature explained as much as 82 and 48% of the variance in lower limb bone J among controls and athletes, respectively.DiscussionResults highlight the importance of considering relevant muscle function variables (e.g., force and lever arm lengths) when interpreting behavioral signatures from skeletal remains. Future work to improve the estimation of muscle force from skeletal remains, and incorporate it with lever arm length into analyses, is warranted. Results also suggest that, in doing so, functional relationships between a given section location and musculature should be considered.
Highlights
Biological anthropologists often utilize variation in limb bone diaphyseal cross-sectional geometry (CSG) to infer patterns of loading in the past related to locomotion, mobility, and/or habitual behavior
Results of the current study suggest that our potential to explain variation in midshaft diaphyseal bone strength parameters would be improved if we could (a) better estimate functionally relevant muscle force from bone, and (b) incorporate these force estimates alongside bone length into statistical analyses, rather than controlling for the effect of lever arm length as a component of body size standardization
Lower limb bone polar second moments of area exhibited strong relationships with muscle force production, both estimated from mechanography and proxied by muscle areas, but not with power output
Summary
Biological anthropologists often utilize variation in limb bone diaphyseal cross-sectional geometry (CSG) to infer patterns of loading in the past related to locomotion, mobility, and/or habitual behavior. The most mechanically relevant forces acting on the lower limbs, bending and torsion (Ruff & Hayes, 1983), produce stresses about a neutral cross-sectional axis (bending) or centroid (torsion), whose magnitudes are zero at these neutral locations and increase proportionally as distance from them increases (Frankel & Nordin, 1980; Ruff & Hayes, 1983) This means that the addition of bone to the periosteal surface maximizes diaphyseal J, as it is bone fibers in the periosteal region that must resist the majority of stresses during loading (Jepsen, 2009). By quantifying variation in limb bone diaphyseal J within and among populations in the past, bioarchaeological analyses can infer relative amounts of bending/torsion during life based on the bone's functional response, at the periosteal surface
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