Objectives: The examination of cross-sectional properties (CSP) of long bones can inform about differential activity patterns and levels of mobility. Typically, these analyses have focused on the femur and tibia, but metatarsals might also be informative.This study examines femora, tibiae, and first metatarsals to evaluate the relationships between long bone CSP within the lower limb and how this might improve our interpretations of metatarsal variability. Materials and Methods:The study includes protohistoric Andaman Islanders (n = 26) and Later Stone Age (LSA) Southern Africans (n = 25) from approximately 10,000-500 BP. Skeletal data were acquired from past studies of these groups. Correlations were used to evaluate the relationships between CSP of lower limb bones within individuals. Principal component analyses were used to evaluate how each lower limb bone contributed to variation in CSP among individuals. Results:The correlations between the CSP in the femur and tibia were always strong, but the correlations with the first metatarsal are variable. Variation in femoral loading largely drove PCAs, with less influence by the first metatarsal, or loading in the opposite direction.Discussion: The femur and tibia experience similar patterns of mechanical loading, specifically in compression and tension, but the first metatarsal does not reflect the same biomechanical patterns as the femur and tibia. Similarly, the first metatarsal often drove variation in the opposite direction as the femur, indicating differences in the mechanical loading pattern between the two bones.

Objectives: The Dmanisi Homo fossils include a tibia with a low degree of torsion and metatarsals with a pattern of robusticity differing from modern humans. It has been proposed that low tibial torsion would cause a low foot progression angle (FPA) in walking, and consequently increased force applied to the medial rays. This could explain the more robust MT III and IV from Dmanisi. Here we experimentally tested these hypothesized biomechanical relationships in living human subjects. Materials and Methods:We measured transmalleolar axis (TMA, a proxy for tibial torsion), FPA, and plantar pressure distributions during walking in young men (n = 40). TMA was measured externally using a newly developed method. A pressure mat recorded FPA and pressure under the metatarsal heads (MT I vs. MT II-IV vs. MT V).Results: TMA is positively correlated with FPA, but only in the right foot. Plantar pressure under MT II-IV does increase with lower TMA, as predicted, but FPA does not affect pressure. Body mass index also influenced plantar pressure distribution.Discussion: Lower tibial torsion in humans is associated with slightly increased pressures along the middle rays of the foot during walking, but not because of changes in FPA. Therefore, it is possible that the low degree of torsion in the Dmanisi Homo tibia is related to the unusual pattern of robusticity in the associated metatarsals, but the mechanism behind this relationship is unclear. Future work will explore TMA, FPA, and plantar pressures during running.