Chasing footprints in time – reframing our understanding of human foot function in the context of current evidence and emerging insights

Abstract

In this narrative review we evaluate foundational biomechanical theories of human foot function in light of new data acquired with technology that was not available to early researchers. The formulation and perpetuation of early theories about foot function largely involved scientists who were medically trained with an interest in palaeoanthropology, driven by a desire to understand human foot pathologies. Early observations of people with flat feet and foot pain were analogized to those of our primate ancestors, with the concept of flat feet being a primitive trait, which was a driving influence in early foot biomechanics research. We describe the early emergence of the mobile adaptor–rigid lever theory, which was central to most biomechanical theories of human foot function. Many of these theories attempt to explain how a presumed stiffening behaviour of the foot enables forward propulsion. Interestingly, none of the subsequent theories have been able to explain how the foot stiffens for propulsion. Within this review we highlight the key omission that the mobile adaptor–rigid lever paradigm was never experimentally tested. We show based on current evidence that foot (quasi‐)stiffness does not actually increase prior to, nor during propulsion. Based on current evidence, it is clear that the mechanical function of the foot is highly versatile. This function is adaptively controlled by the central nervous system to allow the foot to meet the wide variety of demands necessary for human locomotion. Importantly, it seems that substantial joint mobility is essential for this function. We suggest refraining from using simple, mechanical analogies to explain holistic foot function. We urge the scientific community to abandon the long‐held mobile adaptor–rigid lever paradigm, and instead to acknowledge the versatile and non‐linear mechanical behaviour of a foot that is adapted to meet constantly varying locomotory demands.

Human foot form and function: variable and versatile, yet sufficiently related to predict function from form

“…Dissecting the foot into isolated components might also, as cautioned by Gould & Lewontin [28], result in looking for and proposing form-function relationships where none exists. Furthermore, Behling et al [29], in their comprehensive review of the literature on human foot function to date, assert that evidence supporting theories of the foot acting as a mobile adaptor and rigid lever (centred around the MLA) is poor at best. Consequently, they, along with several others [30][31][32], advocate acknowledging the structural complexity and functional versatility of our feet.…”

Mitigating Stress: Exploring how our feet change shape with size

“…The human hindfoot complex is unique in shape compared to other non-human primates with specific adaptations to enable habitual upright locomotion (10)(11)(12). Compared to nonhuman primates, the human calcaneus is larger and more robust, presumably to accommodate increased ground reaction forces, and muscular forces applied by the Achilles tendon (12)(13)(14).…”

Humanin vivomidtarsal and subtalar joint kinematics during walking, running, and hopping

“…However, quantifying in vivo midtarsal and subtalar joint motion is challenging. The rare data that has been captured has often been used to test the incorrect assumption that the foot becomes rigid during push-off [6][7][8][9], which is still a common misconception of foot function. It was previously suggested that the large variation in bone shape has the potential to modify midtarsal complex and subtalar joint function [10][11][12][13].We propose to investigate the function of the midtarsal complex and subtalar joint under a more modern framework that views the foot as a highly mobile structure [6], while accounting for the underlying morphology.…”