Locomotion through the environment is important because movement provides access to key resources, including food, shelter and mates. Central to many locomotion-focused questions is the need to understand internal forces, particularly muscle forces and joint reactions. Musculoskeletal modelling, which typically harnesses the power of inverse dynamics, unites experimental data that are collected on living subjects with virtual models of their morphology. The inputs required for producing good musculoskeletal models include body geometry, muscle parameters, motion variables and ground reaction forces. This methodological approach is critically informed by both biological anthropology, with its focus on variation in human form and function, and mechanical engineering, with a focus on the application of Newtonian mechanics to current problems. Here, we demonstrate the application of a musculoskeletal modelling approach to human walking using the data of a single male subject. Furthermore, we discuss the decisions required to build the model, including how to customize the musculoskeletal model, and suggest cautions that both biological anthropologists and engineers who are interested in this topic should consider.

Reconstructing the locomotor behavior of extinct animals depends on elucidating the principles that link behavior, function, and morphology, which can only be done using extant animals. Within the human lineage, the evolution of bipedalism represents a critical transition, and evaluating fossil hominins depends on understanding the relationship between lower limb forces and skeletal morphology in living humans. As a step toward that goal, here we use a musculoskeletal model to estimate forces in the lower limb muscles of ten individuals during walking. The purpose is to quantify the consistency, timing, and magnitude of these muscle forces during the stance phase of walking. We find that muscles which act to support or propel the body during walking demonstrate the greatest force magnitudes as well as the highest consistency in the shape of force curves among individuals. Muscles that generate moments in the same direction as, or orthogonal to, the ground reaction force show lower forces of greater variability. These data can be used to define the envelope of load cases that need to be examined in order to understand human lower limb skeletal load bearing.

In his classic research, Morton established two functionally different configurations of the bipedal and non-bipedal primate foot: one optimized for stability, with a stiff longitudinal arch and adducted first metatarsal, and the other for compliance. Modern human feet were seen as conforming to the bipedal norm and variation from it as pathology, even though clinical evidence has been clear that variation from the norm of a stiff longitudinal arch or adducted first metatarsal exists. This study aims to document the variation in linear and angular measurements of the foot, using weight-bearing radiographs of 50 randomly selected people (25 men) from an urban US Level 1 trauma center. The radiographs were obtained to "rule-out" a foot fracture after trauma or as comparison films for a contralateral foot injury. Measurements were made using Osirix and correlations among the angular and length measurements were determined using Stata with P < 0.05 and Bonferroni correction for multiple comparisons. We found that foot length was not correlated with angular measurements, except for the angle between the first and fifth metatarsal. People with lower medial longitudinal arches also had more abducted first metatarsals and more vertical posterior facets, in accordance with Morton's foot types. Whether or not this variation in modern humans is linked to functionally important consequences remains to be determined in future research. With the new evidence of a more variable foot structure in fossil hominins, understanding the relationship between foot morphology and function becomes more urgent. Anat Rec, 296:1526Rec, 296: -1533Rec, 296: , 2013. V C 2013 Wiley Periodicals, Inc.Key words: Morton's foot types; arch; angles Conventional wisdom has dictated for almost a century that to be effective, the bipedal foot of a hominin is required to have both a medial longitudinal arch and an adducted (or in-line) first metatarsal (Morton, 2007; Elftman and Manter, 2009). This belief originated in the presence of clinical experience which indicated that many modern human feet are flat (planus) and/or have first metatarsals that substantially diverge from the longitudinal axis of the foot (Morton, 1924a,b) and that these conditions are associated with pain and dysfunction. With this paradigm in place, the extremes of variability in foot morphology of humans have been generally understood as representative of inherent pathology (Kanatli et al., 2012; Pique-Vidal, 1924d) and, therefore, not of interest in understanding the evolution and function of foot