Human Bipedalism Research Articles

The influence of multiple variables on bipedal context in wild chimpanzees: implications for the evolution of bipedality in hominins

Investigations into the role of selection in the origin of human bipedalism using ape models have relied heavily on behavioral frequency data. However, analysis of video of wild apes has the advantage of capturing the details of the entirety of each rare, brief bipedal bout witnessed, not just the moment detected in observational studies. We used video to explore the behavioral context and effects of several variables on bipedalism across all ages in wild forest-dwelling chimpanzees from Ngogo, Uganda. We found, as in earlier studies, that adult chimpanzees used bipedalism in the context of foraging; however, unlike earlier studies, we found that while foraging was the predominant behavioral context during arboreal bipedalism, terrestrial bipedalism was more varied in contextual composition. We also found that these different behavioral contexts of bipedalism were associated with different variables. Specifically, foraging was associated with arboreality, hand assistance, and adulthood; antagonism was associated with adulthood, locomotion, and males; play was associated with terrestriality and subadulthood; and travel was associated with locomotion and females. Given that several variables influence bipedalism across multiple behavioral contexts in chimpanzees, it is likely that the early evolution of human bipedalism occurred under the influence of numerous factors. This exploratory study thus suggests that more comprehensive models should be used when reconstructing the transition to bipedalism from the Last Common Ancestor of humans and chimpanzees.

Lufengpithecus inner ear provides evidence of a common locomotor repertoire ancestral to human bipedalism

Various lines of evidence have been used to infer the origin of human bipedalism, but the paucity of hominoid postcranial fossils and the diversity of inferred locomotor modes have tended to confound the reconstruction of ancestral morphotypes. Examination of the bony labyrinth morphology of the inner ear of extinct and living hominoids provides independent evidence for inferring the evolution of hominoid locomotor patterns. New computed tomography data and morphometric analyses of the Late Miocene ape Lufengpithecus indicate that it and other stem great apes possess labyrinths similar to one another and show that hominoids initially evolved from a positional repertoire that included orthogrady, below-branch forelimb suspension and progression, above-branch bipedalism, climbing, clambering, and leaping (hylobatid-like) to one that comprised above-branch quadrupedalism, below-branch forelimb suspension, vertical climbing, limited leaping, terrestrial quadrupedal running and walking, possibly with knuckle walking, and short bouts of bipedalism (chimpanzee-like). The bony labyrinth morphology of Lufengpithecus indicates that it probably conforms more closely to the last common ancestors of crown hominoids and hominids in its locomotor behavior than do other Miocene hominoids. Human bipedalism evolved from this common archetypal Lufengpithecus-like locomotor repertoire. The low evolutionary rate of semicircular canal morphology suggests that Lufengpithecus experienced a relative stasis in locomotor behavior, probably due to the uplift of the Tibetan Plateau, which created a stable environment in the Miocene of southwestern China.

Exploring the effects of skeletal architecture and muscle properties on bipedal standing in the common chimpanzee (Pan troglodytes) from the perspective of biomechanics.

Introduction: It is well known that the common chimpanzee, as both the closest living relative to humans and a facultative bipedal, has the capability of bipedal standing but cannot do so fully upright. Accordingly, they have been of exceeding significance in elucidating the evolution of human bipedalism. There are many reasons why the common chimpanzee can only stand with its hips-knees bent, such as the distally oriented long ischial tubercle and the almost absent lumbar lordosis. However, it is unknown how the relative positions of their shoulder-hip-knee-ankle joints are coordinated. Similarly, the distribution of the biomechanical characteristics of the lower-limb muscles and the factors that affect the erectness of standing as well as the muscle fatigue of the lower limbs remain a mystery. The answers are bound to light up the evolutional mechanism of hominin bipedality, but these conundrums have not been shed much light upon, because few studies have comprehensively explored the effects of skeletal architecture and muscle properties on bipedal standing in common chimpanzees. Methods: Thus, we first built a musculoskeletal model comprising the head-arms-trunk (HAT), thighs, shanks, and feet segments of the common chimpanzee, and then, the mechanical relationships of the Hill-type muscle-tendon units (MTUs) in bipedal standing were deduced. Thereafter, the equilibrium constraints were established, and a constrained optimization problem was formulated where the optimization objective was defined. Finally, thousands of simulations of bipedal standing experiments were performed to determine the optimal posture and its corresponding MTU parameters including muscle lengths, muscle activation, and muscle forces. Moreover, to quantify the relationship between each pair of the parameters from all the experimental simulation outcomes, the Pearson correlation analysis was employed. Results: Our results demonstrate that in the pursuit of the optimal bipedal standing posture, the common chimpanzee cannot simultaneously achieve maximum erectness and minimum muscle fatigue of the lower limbs. For uni-articular MTUs, the relationship between muscle activation, relative muscle lengths, together with relative muscle forces, and the corresponding joint angle is generally negatively correlated for extensors and positively correlated for flexors. For bi-articular MTUs, the relationship between muscle activation, coupled with relative muscle forces, and the corresponding joint angles does not show the same pattern as in the uni-articular MTUs. Discussion: The results of this study bridge the gap between skeletal architecture, along with muscle properties, and biomechanical performance of the common chimpanzee during bipedal standing, which enhances existing biomechanical theories and advances the comprehension of bipedal evolution in humans.

Functional significance of vertical free moment for generation of human bipedal walking

In human bipedal walking, the plantar surface of the foot is in contact with the floor surface, so that a vertical free moment (VFM), a torque about a vertical axis acting at the centre-of-pressure due to friction between the foot and the ground, is generated and applied to the foot. The present study investigated the functional significance of the VFM in the mechanics and evolution of human bipedal walking by analysing kinematics and kinetics of human walking when the VFM is selectively eliminated using point-contact shoes. When the VFM was selectively eliminated during walking, the thorax and pelvis axially rotated in-phase, as opposed to normal out-of-phase rotation. The amplitudes of the axial rotation also significantly increased, indicating that the VFM greatly contributes to stable and efficient bipedal walking. However, such changes in the trunk movement occurred only when arm swing was restricted, suggesting that the VFM is critical only when arm swing is restrained. Therefore, the human plantigrade foot capable of generating large VFM is possibly adaptive for bipedal walking with carrying food, corroborating with the so-called provisioning hypothesis that food carrying in the early hominins is a selective pressure for the evolution of human bipedalism.

Coordination within paraspinal muscles during bipedalism in humans, a white-handed gibbon, and a Japanese macaque

Coordination within paraspinal muscles during bipedalism in humans, a white-handed gibbon, and a Japanese macaque

Walks of Life: Mounting fossil evidence is upending the conventional wisdom about the evolution of human bipedalism.

Walks of Life: Mounting fossil evidence is upending the conventional wisdom about the evolution of human bipedalism.

The Role of the Transverse Arch in Progressive Collapsing Foot Deformity (PCFD): A Retrospective Case Control Study

Category: Midfoot/Forefoot; Basic Sciences/Biologics; Hindfoot Introduction/Purpose: A recent study published in Nature (Venkadesan et al.) demonstrated that coupling the transverse arch (TA) with the medial longitudinal arch (MLA) significantly increased midfoot intrinsic stiffness. The contribution of the TA is substantial, suggested as the evolutionary advancement providing the foot stiffness required for human bipedalism. Progressive collapsing foot deformity (PCFD) is a complex deformity ultimately resulting in loss of stiffness and collapse of the MLA. The novel understanding of the TA may play a key role in the pathogenesis of this deformity. The objectives of this study were to assess and compare the TA curvature in PCFD and controls and to evaluate its relationship with accepted PCFD measures. We hypothesized that the curvature of the TA will be decreased in PCFD. Methods: A retrospective review was conducted for 32 PCFD and 32 controls. Measurements were performed using weight- bearing CT (WBCT). A novel measurement, the transverse arch plantar (TAP) angle, was designed to directly measure the TA in both PCFD (Figure 1a) and controls (Figure 1b). TA curvature was calculated using the equation described by Venkadesan et al. (Figure 6) utilizing width, length (Figure 3a), 3rd metatarsal thickness (Figure 3b), and 4th metatarsal torsion (Figure 4a, 4b). Finally, uni- and multivariate analyses were performed to analyze the relationship between the TAP angle, Foot and Ankle Offset (FAO), peritalar subluxation, and measurements associated with PCFD classes: hindfoot moment arm (class A), talonavicular coverage angle (class B), Meary angle (class C), medial facet uncoverage angle (class D), and talar tilt (class E). Normality of different variables was assessed using the Shapiro-Wilk test. Two groups were compared using t-test for normal, and Mann-Whitney for non-normal variables. Results: Measurements of the TAP angle were found to be significantly higher in the PCFD group than the control group with a mean angle of 115.24° (SD 10.68) and 100.76° (SD 7.92) respectively (p<0.001) (Figure 2).No significant difference was found in the calculated TA curvature between PCFD and controls with mean values of 17.84 (SD 4.41) and 18.18 (SD 3.68) respectively (p=0.741) (Figure 5).The univariate analysis performed showed a moderate positive correlation between the TAP angle and the FAO (ρ=0.58;r2=0.34;p <0.001).The multivariate analyses showed, among the different PCFD class measurements and the TAP angle, only the middle facet uncoverage (β=0.08,p<0.001) and hindfoot moment arm (β=0.32, p<0.001) were associated with higher values of FAO, while only the Meary (β=0.49,p=0.004) and the talonavicular coverage angles were associated with higher values of peritalar subluxation (β=0.75,p<0.001). Whereas, Meary's angle was the only predictive factor of higher TA collapse (β=0.55,p<0.001). Conclusion: Our direct measurement showed a collapsed of the TA in PCFD. However, this did not appear to be a consequence of insufficient bone torsion, but rather some other etiology, possibly a soft tissue failure. Considering the implication of the TA among the different PCFD classes, it did not appear to play a significant role on the overall PCFD deformity. TA collapse seemed mainly influenced by Meary's angle, which assess the MLA. This further supports the idea behind TA and MLA coupling suggesting that when the TA is collapsed, the foot does not possess the required stiffness to maintain the MLA.

Objective Assessment of Cardiopostural Control and its Improvement after Yoga Training using Wii Balance Board and Heart Rate Variability in Young Girls with Flat Foot

Objective: Bipedalism in humans demanded robust postural control systems to maintain balance and equilibrium during variety of volitional activities. Adaptive learning is a key characteristic of these control systems. Postural control and balance are associated with autonomic changes trying to maintain cardiovascular homeostasis during postural imbalances, which are specifically important in conditions like flat foot. Yoga training could help such cases to achieve better postural balance and autonomic state. Young adolescent girls with flat foot were studied in comparison to normal girls and flat foot boys. Materials and Methods: Sixteen girls and 11 boys with flat foot were subjected to posturography on Wii Balance Board connected wirelessly to PowerLab 15T. Wireless heart rate belt was used to acquire RR intervals. Vrikshasana was chosen as the suitable asana for 4-week training. Displacement of center of pressure (COP) and heart rate variability was analyzed using LabChart pro software before and after yoga training. Results: COP displacement in flat foot subjects is away from the center during erect stance and sway toward sides. Flat foot girls showed significant greater displacements and lesser correction after yoga compared to flat foot boys (P < 0.05). Flat foot girls also showed lesser recovery in LF% and RMSSD after 4-week yoga training. Conclusion: Studying the autonomic changes during voluntary postural imbalance on balance board provide real-time picture of internal state in flat foot individuals. The sympathetic dominance would account for preparedness and adaptation in postural control systems. This state improved with yoga training toward better cardiac vagal tone.

Unperceived motor actions of the balance system interfere with the causal attribution of self-motion.

The instability of human bipedalism demands that the brain accurately senses balancing self-motion and determines whether movements originate from self-generated actions or external disturbances. Here, we challenge the longstanding notion that this process relies on a single representation of the body and world to accurately perceive postural orientation and organize motor responses to control balance self-motion. Instead, we find that the conscious sense of balance can be distorted by the corrective control of upright standing. Using psychophysics, we quantified thresholds to imposed perturbations and balance responses evoking cues of self-motion that are (in)distinguishable from corrective balance actions. When standing immobile, participants clearly perceived imposed perturbations. Conversely, when freely balancing, participants often misattributed their own corrective responses as imposed motion because their balance system had detected, integrated, and responded to the perturbation in the absence of conscious perception. Importantly, this only occurred for perturbations encoded ambiguously with balance-correcting responses and that remained below the natural variability of ongoing balancing oscillations. These findings reveal that our balance system operates on its own sensorimotor principles that can interfere with causal attribution of our actions, and that our conscious sense of balance depends critically on the source and statistics of induced and self-generated motion cues.

Human talar ontogeny: Insights from morphological and trabecular changes during postnatal growth

AbstractObjectivesThe study of the development of human bipedalism can provide a unique perspective on the evolution of morphology and behavior across species. To generate new knowledge of these mechanisms, we analyze changes in both internal and external morphology of the growing human talus in a sample of modern human juveniles using an innovative approach.Materials and MethodsThe sample consists of high‐resolution microCT scans of 70 modern juvenile tali, aged between 8 postnatal weeks and 10 years old, from a broad chronological range from Middle/Late Neolithic, that is, between 4800 and 4500 BCE, to the 20th century. We applied geometric morphometric and whole‐bone trabecular analysis (bone volume fraction, degree of anisotropy, trabecular number, thickness, and spacing) to all specimens to identify changes in the external and internal morphology during growth. Morphometric maps were also generated.ResultsDuring the first year of life, the talus has an immature and globular shape, with a dense, compact, and rather isotropic trabecular architecture, with numerous trabeculae packed closely together. This pattern changes while children acquire a more mature gait, and the talus tends to have a lower bone volume fraction, a higher anisotropy, and a more mature shape.DiscussionThe changes in talar internal and external morphologies reflect the different loading patterns experienced during growth, gradually shifting from an “unspecialized” morphology to a more complex one, following the development of bipedal gait. Our research shows that talar plasticity, even though genetically driven, may show mechanical influences and contribute to tracking the main locomotor milestones.

인간 진화에 따른 다리 근육 및 발 결합조직의 변화 개관

Purpose: The purpose of this study is to review important changes in studies on plantaris, peroneus tertius, and plantar aponeurosis according to human evolution.BR Method: For this overview study, we searched papers published in Pubmed by 2021. The keywords of the search engine were leg muscle, evolution, plantaris, peroneus tertius, plantar aponeurosis, and plantar fascia. Research papers related to primates were excluded from this study. A total of 22 papers, including 8 papers related to the plantaris, 9 papers related to the peroneus tertius, and 5 papers related to the plantar aponeurosis were accepted and analyzed for this overview.BR Results: Plantaris is a vestigial muscle but has recently been shown to be a useful graft for the lateral ankle ligament and hand tendon. Peroneus tertius is a human-specific muscle that serves to parallelize the sole of the foot to the ground for adaptation to bipedal gait and its final evolution seems not to be finished yet. Plantar aponeurosis has been shown to be an adaptation to evolved human bipedal walking while providing a unique windlass mechanism in cooperation with longitudinal arch.BR Conclusion: In conclusion, plantaris, peroneus tertius, and plantar aponeurosis have undergone important changes along with human bipedalism evolution and are closely related to modern leg and foot injuries. Therefore, this aspect should be considered carefully when diagnosing and treating related leg and foot injuries.

A Biomechanical and Evolutionary Perspective of the Menisci Indicate They Are Not Shock Absorbers

Human bipedalism entails high‐magnitude, short‐duration impact transient forces that occur every heel strike. These transient forces, or ‘shock’, are attenuated as they propagate up the body, and many structures have been proposed as ‘shock absorbers’ within the body. The medial and lateral menisci of the knee are a pair of fibrocartilaginous structures that have often been cited as shock absorbers. However, despite the frequency with which this claim is made in scientific literature, medical education and clinical practice, there is little primary data that supports the notion that the menisci function as shock absorbers.Here we compile evolutionary and biomechanical data to critique this oft‐cited notion. First, we show that the origin of this idea draws on a limited number of studies, each with caveats that make that evidence for a shock absorptive function dubious. We then review evolutionary and comparative evidence to show that human menisci are unremarkable in morphology compared with most other tetrapods. Humans possess two, crescentic‐shaped menisci that are similar in morphology to most mammals and many tetrapods. This suggests that the null hypothesis of meniscal function is one of similarity among tetrapods. Furthermore, we show that among tetrapods, shock during locomotion is uncommon; humans stand out as one of the only tetrapods that regularly experience high levels of shock during locomotion. Thus, a shock‐absorption function does not explain the origin of menisci, nor are human menisci specialized in any way that would explain this unique function during human gait. We further assess the mechanical material properties of menisci and show that the menisci overwhelmingly behave like springs and are poorly suited for energy absorption. We compiled data on phase angle and loss tangent, two properties used to assess energy absorption or release. Loss tangents of the menisci are typically between 0.1–0.2, close to an ideal spring (0.0) as opposed to an energy absorbing damper (>1.0). Similarly, phase angles were generally <10°, more similar to an idealized spring value of 0°, as opposed to a pure damper at 90°. Thus, when deformed menisci release most of this energy as opposed to shock absorbers, which dissipate energy.Finally, we integrated data on material properties of the meniscus and loading data from previous studies to estimate actual meniscal energy absorption in comparison to other known energy‐absorbing structures in the body. The heel pad, a well‐known contributor to absorbing energy from heel strike, absorbed 50–69% (0.70 +/‐ 0.11 J) of impact loading when using realistic loading conditions in vitro. All knee structures combined absorbed 0.12 +/‐ 0.01 J of impact energy, only 6–17% of the energy absorbed by the heel pad alone. Available loading data suggest that energy absorption of the menisci alone likely account for only ~4% of all energy absorption at the knee. Thus, our estimates of the total shock absorption capacity of the menisci is essentially negligible.These findings indicate that the menisci did not originally develop for shock‐absorption in tetrapods and did not develop a specialized shock absorbing function in humans.

A geometric morphometric approach to investigate primate proximal phalanx diaphysis shape.

Current approaches to quantify phalangeal curvature assume that the long axis of the bone's diaphysis approximates the shape of a portion of a circle (included angle method) or a parabola (second-degree polynomial method). Here we developed, tested, and employed an alternative geometric morphometrics-based approach to quantify diaphysis shape of proximal phalanges in humans, apes and monkeys with diverse locomotor behaviors. 100 landmarks of the central longitudinal axis were extracted from 3D surface models and analyzed using 2DGM methods, including Generalized Procrustes Analyses. Principal components analyses were performed and PC1 scores (>80% of variation) represented the dorsopalmar shape of the bone's central longitudinal axis and separated taxa consistently and in accord with known locomotor behavioral profiles. The most suspensory taxa, including orangutans, hylobatids and spider monkeys, had significantly lower PC1 scores reflecting the greatest amounts of phalangeal curvature. In contrast, bipedal humans and the quadrupedal cercopithecoid monkeys sampled (baboons, proboscis monkeys) exhibited significantly higher PC1 scores reflecting flatter phalanges. African ape (gorillas, chimpanzees and bonobos) phalanges fell between these two extremes and were not significantly different from each other. PC1 scores were significantly correlated with both included angle and the a coefficient of a second-degree polynomial calculated from the same landmark dataset, but had a significantly higher correlation with included angles. Our alternative approach for quantifying diaphysis shape of proximal phalanges to investigate dorsopalmar curvature is replicable and does not assume a priori either a circle or parabola model of shape, making it an attractive alternative compared with existing methodologies.

Trabecular structure of the elbow reveals divergence in knuckle-walking biomechanical strategies of African apes.

African apes engage in a distinct form of locomotion called knuckle-walking, but there is much ambiguity as to when and how this locomotor behavior evolved. This study aims to elucidate potential differences in knuckle-walking elbow posture and loading in African apes through the study of trabecular bone. Using a whole-epiphysis approach, we quantified variation in the trabecular structure of the distal humerus of chimpanzees, western lowland gorillas, and mountain gorillas in comparison to orang-utans, siamangs, and a sample of Old and New World monkeys. Results demonstrate differences in the distribution of trabecular bone within the distal humerus that are consistent across taxa that habitually use a flexed-elbow posture in comparison to those that use an extended elbow during locomotion. Western lowland gorillas show an extended-elbow pattern consistent with the straight forelimb position during knuckle-walking, whereas chimpanzees show a flexed-elbow pattern. Unexpectedly, mountain gorillas show an intermediate pattern between their western counterparts and chimpanzees. The differences found in elbow joint posture between chimpanzees and gorillas, and between gorilla species, point to diversification in the knuckle-walking biomechanical strategies among African apes, which has implications in the debate regarding the locomotor behavior from which human bipedalism arose.

Biomechanical study comparing the energy cost of human bipedalism versus zenkutsu-dachi stepping of a karateka.

Traditional stepping in the zenkutsu-dachi stance of the Shotokan style of karate is very physically demanding. It requires considerably more effort than what is expended during conventional human bipedalism. We performed a biomechanical study to analyze and compare these two types of gaits when performed by a highly experienced karateka. The study involved a three-dimensional motion analysis system (digital cameras and optical reflectors) and a force platform to analyze the ground reaction forces in all three planes. The study had both kinematic and kinetic components. We found that zenkutsu-dachi stepping is much more costly from an energetics point of view because the properties of the biarticular muscles are not used, the muscular moments of force are higher, and the body's potential energy is not converted into kinetic energy, contrary to the more economical model of human bipedalism that involves an inverted pendulum pattern.

Transneuronal delivery of designer cytokines: perspectives for spinal cord injury.

Transneuronal delivery of designer cytokines: perspectives for spinal cord injury.

Risk factors for neonatal brachial plexus palsy attributed to anatomy, physiology, and evolution.

The inherent variable anatomy of the neonate and the uniquely-shaped maternal birth canal that is associated with the evolution of human bipedalism constitute risk factors for neonatal brachial plexus palsy (NBPP). For example, those neonates with a prefixed brachial plexus (BP) are at greater risk of trauma due to lateral neck traction during delivery than those with a normal or postfixed BP. Compared to adults, neonates also have extremely large and heavy heads (high head: body ratio) set upon necks with muscles and ligaments that are weak and poorly developed. Accordingly, insufficient cranial stability can place large torques on the cervical spinal nerves. In addition, the pelvic changes necessary for habitual bipedal posture resulted in a uniquely-shaped, obstruction-filled, sinusoidal birth canal, requiring the human fetus to complete a complicated series of rotations to successfully traverse it. Furthermore, although there are many risk factors that are known to contribute to NBPP, the specific anatomy and physiology of the neonate, except for macrosomia, is not considered to be one of them. In fact, currently, the amount of lateral traction applied to the neck during delivery is the overwhelming legal factor that is used to evaluate whether a birth attendant is liable in cases of permanent NBPP. Here, we suggest that the specific anatomy and physiology of the neonate and mother, which are clearly not within the control of the birth attendant, should also be considered when assessing liability in cases of NBPP.

Foot anatomy, walking energetics, and the evolution of human bipedalism

Interspecies differences in locomotor efficiency have been extensively researched, but within-species variation in the metabolic cost of walking and its underlying causes have received much less attention. This is somewhat surprising given the importance of walking energetics to natural selection, and the fact that the mechanical efficiency of striding bipedalism in modern humans is thought to be related in some part to the unique morphology of the human foot. Previous studies of human running have linked specific anatomical traits in the foot to variations in locomotor energetics to provide insight into form-function relationships in human evolution. However, such studies are relatively rare, particularly for walking. In this study, relationships between a range of functional musculoskeletal traits in the human lower limb and the energetics of walking over compliant and noncompliant substrates are examined, with particular focus on the lower limb and foot. Twenty-nine young, healthy individuals walked across three surfaces—a noncompliant laboratory floor, and compliant 6 cm and 13 cm thick foams—at self-selected speeds while oxygen consumption was measured, from which the metabolic cost of transport was calculated. Lower limb lengths, calcaneus lengths, foot shape indices, and maximum isometric plantarflexion torques were also measured and subsequently tested for relationships with metabolic cost over these surfaces using linear regression. It was found that metabolic cost varied considerably between individuals within and across substrate types, but this variation was not statistically related to or explained by variations in musculoskeletal parameters considered to be adaptively important to efficient bipedal locomotion. This therefore provides no supportive evidence that variations in these gross anatomical parameters confer significant advantages to the efficiency of walking, and therefore suggest caution in the use of similar metrics to infer differences in walking energetics in closely related fossil species.

Morphometric profile of tendocalcaneus of South Africans of European ancestry using a cadaveric approach.

Tendocalcaneus is a strong tendon that is vital for bipedalism in humans. Despite its tremendous strength, the tendocalcaneus is prone to damage and degeneration causing mobility problems and pain. Morphometric dimension of the tendocalcaneus is of benefit to the surgical repair and reconstruction of the damaged tendon. Cadaveric approach provides a realistic method for determining tendocalcaneus morphometry and as at present only two cadaveric studies on Indian population is available. Thus this study presents data on tendocalcaneus morphometry in South Africans of European ancestry using a cadaveric approach. A total of 66 lower limbs (32 left and 34 right legs) sourced from 49 male and female cadavers were used. After careful dissection of the posterior aspect of leg, the medial and lateral length, distal width, distal circumference and proximal width of the tendocalcaneus were measured. The data showed a high degree of reproducibility indicating that the measurements obtained using cadaveric approach were precise and accurate. There was no difference in measurements between the sides. Measurements in the males were generally higher than in the females. Strong associations were observed between the paired measurements of the medial and lateral tendon length and between the distal width and distal circumference. The data obtained will be useful in predicting tendocalcaneus size during the surgical reconstruction of the tendocalcaneus.

Forward dynamic simulation of Japanese macaque bipedal\xa0locomotion demonstrates better energetic economy in a virtualised plantigrade posture

A plantigrade foot with a large robust calcaneus is regarded as a distinctive morphological feature of the human foot; it is presumably the result of adaptation for habitual bipedal locomotion. The foot of the Japanese macaque, on the other hand, does not have such a feature, which hampers it from making foot–ground contact at the heel during bipedal locomotion. Understanding how this morphological difference functionally affects the generation of bipedal locomotion is crucial for elucidating the evolution of human bipedalism. In this study, we constructed a forward dynamic simulation of bipedal locomotion in the Japanese macaque based on a neuromusculoskeletal model to evaluate how virtual manipulation of the foot structure from digitigrade to plantigrade affects the kinematics, dynamics, and energetics of bipedal locomotion in a nonhuman primate whose musculoskeletal anatomy is not adapted to bipedalism. The normal bipedal locomotion generated was in good agreement with that of actual Japanese macaques. If, as in human walking, the foot morphology was altered to allow heel contact, the vertical ground reaction force profile became double-peaked and the cost of transport decreased. These results suggest that evolutionary changes in the foot structure were important for the acquisition of human-like efficient bipedal locomotion.