Abstract:The fossil record is scarce and incomplete by nature. Animals and ecological processes devour soft tissue and important bony details over time and, when the dust settles, we are faced with a patchy record full of variation. Fossil taxa are usually defined by craniodental characteristics, so unless postcranial bones are found associated with a skull, assignment to taxon is unstable. Naming a locomotor category based on fossil bone morphology by analogy to living hominoids is not uncommon, and when no single loc… Show more
“…However, as proposed by McClymont et al . [44], given the large degrees of freedom provided by the multiple articulations within our feet, it is likely that the required functions can be obtained with a wide variety of shape configurations. Figure 5Variations in longitudinal and transverse arch shapes as described by the first and second principal components (PC1 and PC2, respectively) of the foot shape model while bearing full bodyweight.…”
Section: Discussionmentioning
confidence: 99%
“…For example, if a specific arched shape was required to provide stiffness for propulsion, or to store and return a given amount of mechanical energy, it could be expected that this shape feature would be tightly constrained across the human species, to deliver the required function [43]. However, as proposed by McClymont et al [44], given the large degrees of freedom provided by the multiple articulations within our feet, it is likely that the required functions can be obtained with a wide variety of shape configurations. Developmental plasticity may also explain some of the variance in general foot shape, deformation and PA stiffness within our dataset.…”
Modern human feet are considered unique among primates in their capacity to transmit propulsive forces and re-use elastic energy. Considered central to both these capabilities are their arched configuration and the plantar aponeurosis (PA). However, recent evidence has shown that their interactions are not as simple as proposed by the theoretical and mechanical models that established their significance. Using three-dimensional foot scans and statistical shape and deformation modelling, we show that the shape of the longitudinal and transverse arches varies widely among the healthy adult population, and that the former is subject to load-induced arch flattening, whereas the latter is not. However, longitudinal arch shape and flattening are only one of the various foot shape–deformation relationships. PA stiffness was also found to vary widely. Yet only a small amount of this variability (approx. 10–18%) was explained by variations in foot shape, deformation and their combination. These findings add to the mounting evidence showing that foot mechanics are complex and cannot be accurately represented by simple models. Especially the interactions between longitudinal arch and PA appear to be far less constrained than originally proposed, most likely due to the many degrees of freedom provided by the structural complexity of our feet.
“…However, as proposed by McClymont et al . [44], given the large degrees of freedom provided by the multiple articulations within our feet, it is likely that the required functions can be obtained with a wide variety of shape configurations. Figure 5Variations in longitudinal and transverse arch shapes as described by the first and second principal components (PC1 and PC2, respectively) of the foot shape model while bearing full bodyweight.…”
Section: Discussionmentioning
confidence: 99%
“…For example, if a specific arched shape was required to provide stiffness for propulsion, or to store and return a given amount of mechanical energy, it could be expected that this shape feature would be tightly constrained across the human species, to deliver the required function [43]. However, as proposed by McClymont et al [44], given the large degrees of freedom provided by the multiple articulations within our feet, it is likely that the required functions can be obtained with a wide variety of shape configurations. Developmental plasticity may also explain some of the variance in general foot shape, deformation and PA stiffness within our dataset.…”
Modern human feet are considered unique among primates in their capacity to transmit propulsive forces and re-use elastic energy. Considered central to both these capabilities are their arched configuration and the plantar aponeurosis (PA). However, recent evidence has shown that their interactions are not as simple as proposed by the theoretical and mechanical models that established their significance. Using three-dimensional foot scans and statistical shape and deformation modelling, we show that the shape of the longitudinal and transverse arches varies widely among the healthy adult population, and that the former is subject to load-induced arch flattening, whereas the latter is not. However, longitudinal arch shape and flattening are only one of the various foot shape–deformation relationships. PA stiffness was also found to vary widely. Yet only a small amount of this variability (approx. 10–18%) was explained by variations in foot shape, deformation and their combination. These findings add to the mounting evidence showing that foot mechanics are complex and cannot be accurately represented by simple models. Especially the interactions between longitudinal arch and PA appear to be far less constrained than originally proposed, most likely due to the many degrees of freedom provided by the structural complexity of our feet.
“…We speculate that this could be because of variation in the morphology of the foot among participants 29 , because of neuromuscular control strategies that divide the work between the lower limb joints differently 30 , or step to step variations as only one step was captured. Due to the participant-specific nature of our results, we suggest avoiding “covering law” statements 31 that discuss overall foot behavior in terms of group averages.…”
The foot acts as the primary interface to the ground during bipedal locomotion. It absorbs and returns energy over stance as the longitudinal arch deforms and recoils. The term "arch recoil" evokes the concept that the foot's returned energy directly propels the centre of mass forward by lifting the talus. However, recent work has shown that arch recoil does not directly drive the body forward; instead, it lowers and posteriorly tilts the talus, putting it into a more favourable position for upright gait. Here, we aim to supply a kinetic explanation for this mechanism. We applied the unified deformable power approach to highly accurate talus kinematics from biplanar videoradiography and force plate measurements to measure the power absorbed/produced by the foot. We coupled these measurements with a simple mathematical model that allowed us to restrict rotation and linear actuation of the talus caused by the recoil of the arch to demonstrate that positive foot power primarily contributes to posteriorly tilting the talus. This suggests the role of positive foot power during propulsion is to keep the talocrural surface in a more favourable position for upright gait rather than directly propelling the centre of mass forwards. These findings highlight that arch mobility during push-off is critical for allowing the ankle to directly propel the body forward and upward during the propulsive phase of gait.
“…There is wide variability in external shape and osseous morphology amongst healthy human feet (McClymont, Davis & Crompton, 2022). This variation provides an excellent opportunity to investigate how variations in shape influence function.…”
“…These morphology–function relationships may be informative in the context of clinical foot pathologies. An important consideration for future research in this area is to ensure that we have diverse data sets representing sex, demographic, and geographic variability (McClymont et al ., 2022).…”
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.
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