ArticlePublisher preview available

Stiffness of the human foot and evolution of the transverse arch


Stiffness of the human foot and evolution of the transverse arch

If you want to read the PDF, try requesting it from the authors.

Abstract and Figures

The stiff human foot enables an efficient push-off when walking or running, and was critical for the evolution of bipedalism1–6. The uniquely arched morphology of the human midfoot is thought to stiffen it5–9, whereas other primates have flat feet that bend severely in the midfoot7,10,11. However, the relationship between midfoot geometry and stiffness remains debated in foot biomechanics12,13, podiatry14,15 and palaeontology4–6. These debates centre on the medial longitudinal arch5,6 and have not considered whether stiffness is affected by the second, transverse tarsal arch of the human foot16. Here we show that the transverse tarsal arch, acting through the inter-metatarsal tissues, is responsible for more than 40% of the longitudinal stiffness of the foot. The underlying principle resembles a floppy currency note that stiffens considerably when it curls transversally. We derive a dimensionless curvature parameter that governs the stiffness contribution of the transverse tarsal arch, demonstrate its predictive power using mechanical models of the foot and find its skeletal correlate in hominin feet. In the foot, the material properties of the inter-metatarsal tissues and the mobility of the metatarsals may additionally influence the longitudinal stiffness of the foot and thus the curvature–stiffness relationship of the transverse tarsal arch. By analysing fossils, we track the evolution of the curvature parameter among extinct hominins and show that a human-like transverse arch was a key step in the evolution of human bipedalism that predates the genus Homo by at least 1.5 million years. This renewed understanding of the foot may improve the clinical treatment of flatfoot disorders, the design of robotic feet and the study of foot function in locomotion. The transverse tarsal arch, acting through the inter-metatarsal tissues, is important for the longitudinal stiffness of the foot and its appearance is a key step in the evolution of human bipedalism.
This content is subject to copyright. Terms and conditions apply.
Nature | Vol 579 | 5 March 2020 | 97
Stiffness of the human foot and evolution of
the transverse arch
Madhusudhan Venkadesan1 ✉, Ali Yawar1, Carolyn M. Eng1,10, Marcelo A. Dias2,3,4,10,
Dhiraj K. Singh5,9, Steven M. Tommasini6, Andrew H. Haims6,7, Mahesh M. Bandi5 ✉ &
Shreyas Mandre8 ✉
The sti human foot enables an ecient push-o when walking or running, and was
critical for the evolution of bipedalism1–6. The uniquely arched morphology of the
human midfoot is thought to stien it5–9, whereas other primates have at feet that
bend severely in the midfoot7,10,11. However, the relationship between midfoot
geometry and stiness remains debated in foot biomechanics12,13, podiatry14,15 and
palaeontology4–6. These debates centre on the medial longitudinal arch5,6 and have
not considered whether stiness is aected by the second, transverse tarsal arch of
the human foot16. Here we show that the transverse tarsal arch, acting through the
inter-metatarsal tissues, is responsible for more than 40% of the longitudinal stiness
of the foot. The underlying principle resembles a oppy currency note that stiens
considerably when it curls transversally. We derive a dimensionless curvature
parameter that governs the stiness contribution of the transverse tarsal arch,
demonstrate its predictive power using mechanical models of the foot and nd its
skeletal correlate in hominin feet. In the foot, the material properties of the inter-
metatarsal tissues and the mobility of the metatarsals may additionally inuence the
longitudinal stiness of the foot and thus the curvature–stiness relationship of the
transverse tarsal arch. By analysing fossils, we track the evolution of the curvature
parameter among extinct hominins and show that a human-like transverse arch was a
key step in the evolution of human bipedalism that predates the genus Homo by at
least 1.5million years. This renewed understanding of the foot may improve the
clinical treatment of atfoot disorders, the design of robotic feet and the study of foot
function in locomotion.
When walking and running, people use the ball of the foot to apply
forces that exceed bodyweight17. Because of these forces, the midfoot
experiences large sagittal-plane torques that bend the foot. A stiff
midfoot reduces the loss of propulsive work due to foot deformation
and helps to efficiently utilize the mechanical power generated by the
ankle during push-off2–4.
The unique arch shape of the human midfoot is thought to underlie
the higher stiffness of human feet compared to other primate feet5,6,9,18
(Extended Data Table1). However, stiffness is not a static quantity and mus-
cle activity can modulate midfoot stiffness in both humans and apes
The static stiffness due to the passive structures of the foot forms the
baseline around which muscles with similar mechanical action as the pas-
sive tissues are likely to modulate stiffness. Therefore, understanding the
morphological features underpinning the static stiffness is crucial for
both static and dynamic conditions (Supplementary Information 1.1–1.3).
The human midfoot has two pronounced arches: the extensively
studied medial longitudinal arch (MLA)5,6,20 and the less-studied
transverse tarsal arch (TTA) (Fig.1a). The MLA stiffens the midfoot
in part through a bow-string arrangement with the stiff longitudinal
fibres of the plantar fascia7,9 and a windlass-like mechanism due to toe
dorsiflexion just before push-off
. In addition to the plantar fascia,
the longitudinally oriented long plantar, short plantar and calcaneona-
vicular ligaments are essential for the static midfoot stiffness in humans
and other primates
. However, in contrast to the plantar fascia, the
contribution of these ligaments does not depend on the height of the
MLA, as shown by their nearly equal relative contributions in both
arched human feet9 and flat monkey feet18 (Extended Data Table1 and
Supplementary Information 1.4).
The relationship between the height or curvature of the MLA and
midfoot stiffness remains controversial5,20. Some people have no dif-
ficulty walking with a heel-to-toe style despite having little to no MLA
Conflicting evidence also emerges in foot disabilities11,22 and surgical
reconstruction of the MLA
when correlating MLA height with foot
flexibility, and casts further doubt on the relationship between the
Received: 29 March 2018
Accepted: 23 January 2020
Published online: 26 February 2020
Check for updates
1Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT, USA. 2School of Science, Aalto University, Espoo, Finland. 3Nordic Institute for Theoretical
Physics (NORDITA), Stockholm, Sweden. 4Department of Engineering, Aarhus University, Aarhus, Denmark. 5Nonlinear and Non-equilibrium Physics Unit, OIST Graduate University, Onna,
Japan. 6Department of Orthopaedics and Rehabilitation, Yale University, New Haven, CT, USA. 7Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA.
8Mathematics Institute, University of Warwick, Coventry, UK. 9Present address: Engineering Mechanics Unit, Jawaharlal Nehru Centre for Advanced Scientiic Research, Bangalore, India.
10These authors contributed equally: Carolyn M. Eng, Marcelo Dias. e-mail:;;
Content courtesy of Springer Nature, terms of use apply. Rights reserved
... The longitudinal ligaments comprise of the short and long plantar ligaments and the spring ligament complex (plantar calcaneonavicular ligament) [9,13]. This appears reasonable, as the midfoot experiences large sagittal-plane torques bending the foot during walking [27,28]. The ligaments thereby provide a static stiffness, and the muscle activity modulates the midfoot stiffness [27]. ...
... This appears reasonable, as the midfoot experiences large sagittal-plane torques bending the foot during walking [27,28]. The ligaments thereby provide a static stiffness, and the muscle activity modulates the midfoot stiffness [27]. Moreover, the plantar ligaments, contrary to the herein observed lateral and dorsal ligaments, are constantly present in humans and apes. ...
Background This study aims to analyze the ligaments of the dorso-lateral calcaneo-cuboid joint and to assess the biomechanical relevance of the bifurcate ligament. Methods 16 specimens were analyzed for their ligamentous anatomy of the dorso-lateral calcaneo-cuboid joint and side-alternating assigned to two groups with varying ligamentous dissection order. The Chopart joint was stressed in plantar, medial, and lateral direction measuring the displacement by an 3D motion tracker for every dissection step. Results 37.5% of specimens had all ligaments (lateral calcaneo-cuboid, dorsal calcaneo-cuboid, bifurcate calcaneo-cuboid, bifurcate calcaneo-navicular), 37.5% were lacking bifurcate´s calcaneo-cuboid-portion, and 25% presented without dorsal calcaneo-cuboid. Biomechanical testing revealed no significant displacement within the calcaneo-cuboid or talo-navicular joint for any stressed state except for axial compression with dissected dorsal talo-navicular joint capsule in Group 2. Conclusion Broad morphological variability and missing significant displacement regardless of its integrity, make the bifurcate ligament appear of limited biomechanical relevance.
... The plantar muscles (Farris et al., 2019;Kelly et al., 2014), ligaments (Bates et al., 2013;Bojsen-Møller, 1979;Ker et al., 1987;Lovejoy et al., 2009), and fascia (Ker et al., 1987;Sichting et al., 2020) work in tandem with the shape and posture of the bones in the medial (Hicks, 1955;H. Elftman and Manter, 1935;Bojsen-Møller, 1979), lateral(McNutt et al., 2018, and transverse arches (Venkadesan et al., 2020) to increase the intrinsic stiffness that enables foot leverage. Specifically, the static height of the medial arch is thought to appreciably influence the arch's intrinsic stiffness, despite the generally weak relationship between arch height and arch vertical mobility (Cornwall and McPoil, 2011;Zifchock et al., 2006). ...
... show evidence of more pronounced medial and transverse structural arches, likely supported by arch-spanning ligaments and muscles (Susman, 1983;Venkadesan et al., 2020). As a result, Homo could better take advantage of arch mobility and its effects on ankle posture and the contractile state of the triceps surae muscles in propulsion. ...
Full-text available
Developing the ability to habitually walk and run upright on two feet is one of the most significant transformations to have occurred in human evolution. Many musculoskeletal adaptations enabled bipedal locomotion, including dramatic structural changes to the foot and, in particular, the evolution of an elevated medial arch (H. Elftman and Manter, 1935). The foot's arched structure has previously been assumed to play a central role in directly propelling the centre of mass forward and upward through leverage about the toes (Herbert Elftman and Manter, 1935) and a spring-like energy recoil (Hicks, 1955). Paradoxically, these roles seemingly require either arch rigidity (for the former) or mobility (for the latter). However, it is unclear whether or how the mobility and height of the medial arch support its propulsive lever function. Here we show, using high-speed biplanar x-ray, that regardless of intraspecific differences in medial arch height, arch recoil enables a longer contact time and favourable propulsive conditions for walking upright on an extended leg. This mechanism presumably helped drive the evolution of the longitudinal arch after our last common ancestor with chimpanzees, who lack this mobility during push-off. We discovered that the previously overlooked navicular-medial cuneiform joint is primarily responsible for this mobility in human arches, suggesting that future morphological investigations of this joint will provide new interpretations of the fossil record. Our work further suggests that enabling the mobility of the longitudinal arch in footwear and surgical interventions is critical for maintaining the ankle's natural propulsive ability.
... In addition, the medial longitudinal arch (MLA) and the transverse tarsal arch (TTA) are calculated as planar angles. These arches are a representation of the midtarsal joint poses due to active and passive foot structures, and are believed to play a major role in stiffening the foot during gait [45]. The medial longitudinal arch is defined as the angle between a proximal and distal 3D vector. ...
... The methodology to determine the marker placement sensitivity has been described in detail previously [36]. In short, ten adults (6 females, 26.8 ± 2.6 years, 176.4 ± 8.1 cm, 67.2 ± 8.5 kg, EU shoe size: 41 ± 2, range [38][39][40][41][42][43][44][45] and nine children (5 female, 10.7 ± 1.9 years, 147.7 ± 12.8 cm, 41.1 ± 10.9 kg, EU shoe size: 36 ± 2, range: 31-38) with asymptomatic feet were included. A set of 21 markers was placed on the right foot and shank, which included all AFM, OFM and RFM markers. ...
Full-text available
Background Foot and ankle joint kinematics are measured during clinical gait analyses with marker-based multi-segment foot models. To improve on existing models, measurement errors due to soft tissue artifacts (STAs) and marker misplacements should be reduced. Therefore, the aim of this study is to define a clinically informed, universally applicable multi-segment foot model, which is developed to minimize these measurement errors. Methods The Amsterdam foot model (AFM) is a follow-up of existing multi-segment foot models. It was developed by consulting a clinical expert panel and optimizing marker locations and segment definitions to minimize measurement errors. Evaluation of the model was performed in three steps. First, kinematic errors due to STAs were evaluated and compared to two frequently used foot models, i.e. the Oxford and Rizzoli foot models (OFM, RFM). Previously collected computed tomography data was used of 15 asymptomatic feet with markers attached, to determine the joint angles with and without STAs taken into account. Second, the sensitivity to marker misplacements was determined for AFM and compared to OFM and RFM using static standing trials of 19 asymptomatic subjects in which each marker was virtually replaced in multiple directions. Third, a preliminary inter- and intra-tester repeatability analysis was performed by acquiring 3D gait analysis data of 15 healthy subjects, who were equipped by two testers for two sessions. Repeatability of all kinematic parameters was assessed through analysis of the standard deviation (σ) and standard error of measurement (SEM). Results The AFM was defined and all calculation methods were provided. Errors in joint angles due to STAs were in general similar or smaller in AFM (≤2.9°) compared to OFM (≤4.0°) and RFM (≤6.7°). AFM was also more robust to marker misplacement than OFM and RFM, as a large sensitivity of kinematic parameters to marker misplacement (i.e. > 1.0°/mm) was found only two times for AFM as opposed to six times for OFM and five times for RFM. The average intra-tester repeatability of AFM angles was σ:2.2[0.9°], SEM:3.3 ± 0.9° and the inter-tester repeatability was σ:3.1[2.1°], SEM:5.2 ± 2.3°. Conclusions Measurement errors of AFM are smaller compared to two widely-used multi-segment foot models. This qualifies AFM as a follow-up to existing foot models, which should be evaluated further in a range of clinical application areas.
... Of these factors, the one most affected by running technique is running economy (Barnes & Kilding, 2015;Saunders et al., 2004), defined as distance travelled per unit of energy expended. Because of our evolutionary history, all humans share key anatomical traits that minimise energy expenditure during running, such as long lower limbs, long Achilles tendons, foot arches and short toes (Bramble & Lieberman, 2004;Holowka & Lieberman, 2018;Rolian et al., 2008;Venkadesan et al., 2020). Nevertheless, running economy can vary substantially between individuals and groups (Barnes & Kilding, 2015), particularly between people who run habitually vs. infrequently (Bransford & Howley, 1977;Morgan et al., 1995). ...
... These adaptations almost certainly originated long ago in the human evolutionary lineage, very likely among early members of Homo during the Early Pleistocene (Bramble & Lieberman, 2004). Examples of such adaptations can be found across diverse systems in our bodies including the musculoskeletal system (Bramble & Lieberman, 2004;Eng et al., 2015;Holowka & Lieberman, 2018;Lieberman et al., 2006;Rolian et al., 2008;Venkadesan et al., 2020), cardiopulmonary system (Bramble & Carrier, 1983;Callison et al., 2019;Shave et al., 2019), thermoregulatory system (Carrier, 1984;Kamberov et al., 2018;Lieberman, 2015) and nervous system (Raichlen et al., 2012;Wallace et al., 2018b). Thus, from a broad evolutionary perspective, regardless of variation in running techniques, humans are in general 'good' runners, or at least we have an evolved natural capacity to run well. ...
Full-text available
Research among non-industrial societies suggests that body kinematics adopted during running vary between groups according to the cultural importance of running. Among groups in which running is common and an important part of cultural identity, runners tend to adopt what exercise scientists and coaches consider to be good technique for avoiding injury and maximizing performance. In contrast, among groups in which running is not particularly culturally important, people tend to adopt suboptimal technique. This paper begins by describing key elements of good running technique, including landing with a forefoot or midfoot strike pattern and leg oriented roughly vertically. Next, we review evidence from non-industrial societies that cultural attitudes about running associate with variation in running techniques. Then, we present new data from Tsimane forager-horticulturalists in Bolivia. Our findings suggest that running is neither a common activity among the Tsimane nor is it considered an important part of cultural identity. We also demonstrate that when Tsimane do run, they tend to use suboptimal technique, specifically landing with a rearfoot strike pattern and leg protracted ahead of the knee (called overstriding). Finally, we discuss processes by which culture might influence variation in running techniques among non-industrial societies, including self-optimization and social learning.
... For example, devices that add stiffness to the foot (e.g., shoes and/or insoles) can enhance the ankle plantar flexor force production via a slower contractile velocity [16], which can afford whole-body metabolic energy savings in some locomotion tasks, such as during fast walking [16]. Moreover, foot structures have inherent mechanisms that may regulate its stiffness (and, hence, the lever function), including structural (e.g., the curvature of the transverse arch [17]) and neuromechanical (e.g., the activation of intrinsic foot muscles [11]) features. All of these studies in young adults may offer a theoretical basis for examining the foot's lever function and its consequences on locomotor performance in older adults. ...
Full-text available
Much of our current understanding of age-related declines in mobility has been aided by decades of investigations on the role of muscle–tendon units spanning major lower extremity joints (e.g., hip, knee and ankle) for powering locomotion. Yet, mechanical contributions from foot structures are often neglected. This is despite the emerging evidence of their critical importance in youthful locomotion. With the rapid growth in the field of human foot biomechanics over the last decade, our theoretical knowledge of young asymptomatic feet has transformed, from long-held views of the foot as a stiff lever and a shock absorber to that of a versatile system that can modulate mechanical power and energy output to accommodate various locomotor task demands. In this perspective review, we predict that the next set of impactful discoveries related to locomotion in older adults will emerge by integrating the novel tools and approaches that are currently transforming the field of human foot biomechanics. By illuminating the functions of the feet in older adults, we envision that future investigations will refine our mechanistic understanding of mobility deficits affecting our aging population, which may ultimately inspire targeted interventions to rejuvenate the mechanics and energetics of locomotion.
... The third layer was two-thirds length (around the transverse arch). This probably enhanced the support of the transverse arch by increasing the arch height [37]. ...
Full-text available
Foot orthotics are recommended for the treatment of hallux valgus. The effects of customized foot orthoses (FOs) designed with both medial longitudinal and transverse arch supports are poorly understood, however. This study aimed to investigate the immediate effect of customized FOs on the plantar pressure and contact area in patients with symptomatic hallux valgus. We recruited 18 patients with a mean hallux valgus angle of 27.3 ± 11.1°. Plantar pressure while walking with FOs or flat insoles (FIs) was monitored with a wireless in-shoe plantar pressure-sensing system. Peak pressure (PP), peak force (PF), pressure-time integral (PTI), force-time integral (FTI), and contact area with FOs and FIs were compared. The PF, PTI, and FTI of the midfoot were significantly higher (p < 0.05), and the PP and PTI of the rearfoot were significantly lower (p < 0.05) with the FOs than the FIs. The FOs significantly increased the contact area of the midfoot and rearfoot (p < 0.05) and reduced the contact area of the forefoot (p < 0.05). These results suggest that customized FOs redistribute plantar pressure and the contact area of the midfoot and rearfoot, improving the functional support of the midfoot for patients with hallux valgus.
... The arch of the foot plays an important role in walking and running [3]. Since the 1960s, with the emergence of foot pressure testing instruments and gait analyzers, the biomechanics of the foot have been researched in more depth. ...
Full-text available
Objective: Cavus foot is a deformity defined by the abnormal elevation of the medial arch of the foot and is a common but challenging occurrence for foot and ankle surgeons. In this review, we mainly aim to provide a comprehensive evaluation of the treatment options available for cavus foot correction based on the current research and our experience and to highlight new technologies and future research directions. Methods: Searches on the PubMed and Scopus databases were conducted using the search terms cavus foot, CMT (Charcot-Marie-Tooth), tendon-transfer, osteotomy, and adult. The studies were screened according to the inclusion and exclusion criteria, and the correction of cavus foot was analyzed based on the current research and our own experience. At the same time, 3D models were used to simulate different surgical methods for cavus foot correction. Results: A total of 575 papers were identified and subsequently evaluated based on the title, abstract, and full text. A total of 84 articles were finally included in the review. The deformities involved in cavus foot are complex. Neuromuscular disorders are the main etiologies of cavus foot. Clinical evaluations including biomechanics, etiology, classification, pathophysiology and physical and radiological examinations should be conducted carefully in order to acquire a full understanding of cavus deformities. Soft-tissue release, tendon-transfer, and bony reconstruction are commonly used to correct cavus foot. Surgical plans need to be customized for different patients and usually involve a combination of multiple surgical procedures. A 3D simulation is helpful in that it allows us to gain a more intuitive understanding of various osteotomy methods. Conclusion: The treatment of cavus foot requires us to make personalized operation plans according to different patients based on the comprehensive evaluation of their deformities. A combination of soft-tissue and bony procedures is required. Bony procedures are indispensable for cavus correction. With the promotion of digital orthopedics around the world, we can use computer technology to design and implement cavus foot operations in the future.
In this paper, the solution method for foot arch index (FAI) based on plantar force measurement was proposed. The entire pelma (EP) was divided into three partitions: posterior heel (HP), lateral side of the sole (SL) and medial side of the sole (SM) according to the three-point support mechanics mechanism of the foot and ankle. A distributed force platform was established to obtain the mean positions of the center of pressure (CoP) trajectories on SL, SM, HP, and EP, which were defined as A, B, C, and O, respectively. Based on the principle that the arch height influences the distance from point O to the boundary of triangle ABC, the area ratio of triangle BOC to triangle ABC was defined as FAI. Arch height index (AHI) measurement of thirty participants by combined calipers was compared with FAI measurement of their right feet. The arches were classified based on AHI, and ANOVA was performed. The Pearson correlation coefficient between the FAI method and the AHI method is 0.79 (p<0.0001). The Bland-Altman analysis showed good agreement. ANOVA indicated FAI was statistically significant (F=18.81,p<0.001), and there were statistical differences between groups. These results suggest that the proposed distributed force measurement method can provide support surface boundary (triangle ABC) information related to point O.
The form-function conceptual framework, which assumes a strong relationship between the structure of a particular trait and its function, has been crucial for understanding morphological variation and locomotion among extant and fossil species across many disciplines. In biological anthropology, it is the lens through which many important questions and hypotheses have been tackled with respect to relationships between morphology and locomotor kinematics, energetics, and performance. However, it is becoming increasingly evident that the morphologies of fossil hominins, apes, and humans can confer considerable locomotor diversity and flexibility, and can do so with a range of kinematics depending on soft tissue plasticity and environmental and cultural factors. This complexity is not built in to traditional biomechanical or mathematical models of relationships between structure and kinematics or energetics, limiting our interpretation of what bone structure is telling us about behaviour in the past. The nine papers presented in this Special Collection together address some of the challenges that variation in the relationship between form and function pose in evolutionary biomechanics, to better characterize the complexity linking structure and function and to provide tools through which we may begin to incorporate some of this complexity into our functional interpretations.
Full-text available
Core concepts offer coherence to the discourse of a scientific discipline and facilitate teaching by identifying large unifying themes that can be tailored to the level of the class and expertise of the instructor. This approach to teaching has been shown to encourage deeper learning that can be integrated across subdisciplines of Biology and has been adopted by several other Biology subdisciplines. However, Comparative Vertebrate Anatomy, although one of the oldest biological areas of study, has not had its core concepts identified. Here, we present five core concepts and seven competencies (skills) for Comparative Vertebrate Anatomy that came out of an iterative process of engagement with the broader community of vertebrate morphologists over a three-year period. The core concepts are: A) Evolution, B) Structure and Function, C) Morphological Development, D) Integration and E) Human anatomy is the result of vertebrate evolution. The core competencies students should gain from the study of comparative vertebrate anatomy are: F) Tree thinking, G) Observation, H) Dissection of specimens, I) Depiction of anatomy, J) Appreciation of the importance of natural history collections, K) Science communication and L) Data integration. We offer a succinct description of each core concept and competency, example learning outcomes that could be used to assess teaching effectiveness and examples of relevant resources for both instructors and students. Additionally, we pose a grand challenge to the community, arguing that the field of Comparative Vertebrate Anatomy needs to acknowledge racism, androcentrism, homophobia, genocide, slavery, and other influences in its history and address their lingering effects in order to move forward as a thriving discipline that is inclusive of all students and scientists and continues to generate unbiased knowledge for the betterment of humanity. Despite the rigorous process used to compile these core concepts and competencies, we anticipate that they will serve as a framework for an ongoing conversation that ensures Comparative Vertebrate Anatomy remains a relevant field in discovery, innovation, and training of future generations of scientists.
Full-text available
Human feet have evolved to facilitate bipedal locomotion, losing an opposable digit that grasped branches in favor of a longitudinal arch (LA) that stiffens the foot and aids bipedal gait. Passive elastic structures are credited with supporting the LA, but recent evidence suggests that plantar intrinsic muscles (PIMs) within the foot actively contribute to foot stiffness. To test the functional significance of the PIMs, we compared foot and lower limb mechanics with and without a tibial nerve block that prevented contraction of these muscles. Comparisons were made during controlled limb loading, walking, and running in healthy humans. An inability to activate the PIMs caused slightly greater compression of the LA when controlled loads were applied to the lower limb by a linear actuator. However, when greater loads were experienced during ground contact in walking and running, the stiffness of the LA was not altered by the block, indicating that the PIMs’ contribution to LA stiffness is minimal, probably because of their small size. With the PIMs blocked, the distal joints of the foot could not be stiffened sufficiently to provide normal push-off against the ground during late stance. This led to an increase in stride rate and compensatory power generated by the hip musculature, but no increase in the metabolic cost of transport. The results reveal that the PIMs have a minimal effect on the stiffness of the LA when absorbing high loads, but help stiffen the distal foot to aid push-off against the ground when walking or running bipedally.
Full-text available
Bipedalism is a hallmark of being human and the human foot is modified to reflect this unique form of locomotion. Leonardo da Vinci is credited with calling the human foot “a masterpiece of engineering and a work of art.” However, a scientific approach to human origins has revealed that our feet are products of a long, evolutionary history in which a mobile, grasping organ has been converted into a propulsive structure adapted for the rigors of bipedal locomotion. Reconstructing the evolutionary history of foot anatomy benefits from a fossil record; yet, prior to 1960, the only hominin foot bones recovered were from Neandertals. Even into the 1990s, the human foot fossil record consisted mostly of fragmentary remains. However, in the last two decades, the human foot fossil record has quadrupled, and these new discoveries have fostered fresh new perspectives on how our feet evolved. In this review, we document anatomical differences between extant ape and human foot bones, and comprehensively examine the hominin foot fossil record. Additionally, we take a novel approach and conduct a cladistics analysis on foot fossils (n = 19 taxa; n = 80 characters), and find strong evidence for mosaic evolution of the foot, and a variety of anatomically and functionally distinct foot forms as bipedal locomotion evolved.
Full-text available
Adaptive explanations for modern human foot anatomy have long fascinated evolutionary biologists because of the dramatic differences between our feet and those of our closest living relatives, the great apes. Morphological features, including hallucal opposability, toe length and the longitudinal arch, have traditionally been used to dichotomize human and great ape feet as being adapted for bipedal walking and arboreal locomotion, respectively. However, recent biomechanical models of human foot function and experimental investigations of great ape locomotion have undermined this simple dichotomy. Here, we review this research, focusing on the biomechanics of foot strike, push-off and elastic energy storage in the foot, and show that humans and great apes share some underappreciated, surprising similarities in foot function, such as use of plantigrady and ability to stiffen the midfoot. We also show that several unique features of the human foot, including a spring-like longitudinal arch and short toes, are likely adaptations to long distance running. We use this framework to interpret the fossil record and argue that the human foot passed through three evolutionary stages: first, a great ape-like foot adapted for arboreal locomotion but with some adaptations for bipedal walking; second, a foot adapted for effective bipedal walking but retaining some arboreal grasping adaptations; and third, a human-like foot adapted for enhanced economy during long-distance walking and running that had lost its prehensility. Based on this scenario, we suggest that selection for bipedal running played a major role in the loss of arboreal adaptations.
Full-text available
Fish behaviour and its ecological niche require modulation of its fin stiffness. Using mathematical analyses of rayed fish fins, we show that curvature transverse to the rays is central to fin stiffness. We model the fin as rays with anisotropic bending that are connected by an elastic membrane. For fins with transverse curvature, external loads that bend the rays also splay them apart, which stretches the membrane. This coupling, between ray bending and membrane stretching, underlies the curvature-induced stiffness. A fin that appears flat may still exhibit bending-stretching coupling if the principal bending axes of adjacent rays are misaligned by virtue of intrinsic geometry, i.e. morphologically flat yet functionally curved. Analysis of the pectoral fin of a mackerel shows such functional curvature. Furthermore, as identified by our analyses, the mackerel's fin morphology endows it with the potential to modulate stiffness over a wide range.
Full-text available
Previous studies of human locomotion indicate that foot and ankle structures can interact in complex ways. The structure of the foot defines the input and output lever arms that influences the force-generating capacity of the ankle plantar flexors during push-off. At the same time, deformation of the foot may dissipate some of the mechanical energy generated by the plantar flexors during push-off. We investigated this foot-ankle interplay during walking by adding stiffness to the foot through shoes and insoles, and characterized the resulting changes in in vivo soleus muscle-tendon mechanics using ultrasonography. Added stiffness decreased energy dissipation at the foot (p < 0.001) and increased the gear ratio (i.e., ratio of ground reaction force and plantar flexor muscle lever arms) (p < 0.001). Added foot stiffness also altered soleus muscle behaviour, leading to greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001). Despite this shift in force-velocity behaviour, the whole-body metabolic cost during walking increased with added foot stiffness (p < 0.001). This increased metabolic cost is likely due to the added force demand on the plantar flexors, as walking on a more rigid foot/shoe surface compromises the plantar flexors’ mechanical advantage.
Full-text available
Modern humans are characterized by a highly specialized foot that reflects our obligate bipedalism. Our understanding of hominin foot evolution is, although, hindered by a paucity of well-associated remains. Here we describe the foot of Homo naledi from Dinaledi Chamber, South Africa, using 107 pedal elements, including one nearly-complete adult foot. The H. naledi foot is predominantly modern human-like in morphology and inferred function, with an adducted hallux, an elongated tarsus, and derived ankle and calcaneocuboid joints. In combination, these features indicate a foot well adapted for striding bipedalism. However, the H. naledi foot differs from modern humans in having more curved proximal pedal phalanges, and features suggestive of a reduced medial longitudinal arch. Within the context of primitive features found elsewhere in the skeleton, these findings suggest a unique locomotor repertoire for H. naledi, thus providing further evidence of locomotor diversity within both the hominin clade and the genus Homo.
The evolutionary pressures shaping humans’ unique bipedal locomotion have been a focus of research since Darwin, but the origins of humans’ economical walking gait and endurance running capabilities remain unclear. Here, I review the anatomical and physiological determinants of locomotor economy (e.g., limb length and posture) and endurance (e.g., muscle volume and fiber type) and investigate their development in the hominin fossil record. The earliest hominins were bipedal but retained ape-like features in the hind limb that would have limited their walking economy compared to living humans. Moreover, the evolution of bipedalism and the loss of the forelimbs in weight support and propulsion would have reduced locomotor endurance in the earliest hominins and likely restricted ranging. Australopithecus evinced longer hind limbs, extended limb posture, and a stiff midfoot, suggesting improved, human-like economy, but were likely still limited in their endurance compared to modern humans. The appearance of skeletal traits related to endurance (e.g., larger limb joints, spring-like plantar arch) in Homo was somewhat mosaic, with the full endurance suite apparent only ∼1 million years ago. The development of endurance capabilities in Homo appears to parallel the evolutionary increase in brain size, cognitive sophistication, and metabolic rate.
The postnatal growth of Japanese monkeys (Macaca fuscata) was analyzed cross-sectionally by the Spline Function method. Growth patterns were expressed by both distance and velocity curves. The entire growth period of the Japanese monkey is composed of four stages: from birth to two years of age when the growth velocity decreases rapidly; from two to three and a half (in females) or four and a half (in males) years of age when the velocity stays constant or growth accelerates; from those ages to eight years of age when the velocity decreases again to zero; and after eight years of age when growth no longer occurs. The sex difference between ages at full maturation is not large. Variations in growth patterns were compared among four groups of Japanese monkeys: the Koshima, Shiga and Yakushima groups and a Standard group. Characteristics of growth patterns were also compared among several species of Cercopithecids.
Striding bipedalism is a key derived behaviour of hominids that possibly originated soon after the divergence of the chimpanzee and human lineages. Although bipedal gaits include walking and running, running is generally considered to have played no major role in human evolution because humans, like apes, are poor sprinters compared to most quadrupeds. Here we assess how well humans perform at sustained long-distance running, and review the physiological and anatomical bases of endurance running capabilities in humans and other mammals. Judged by several criteria, humans perform remarkably well at endurance running, thanks to a diverse array of features, many of which leave traces in the skeleton. The fossil evidence of these features suggests that endurance running is a derived capability of the genus Homo, originating about 2 million years ago, and may have been instrumental in the evolution of the human body form.