Biomechanics and the origins of human bipedal walking: The last 50 years.

Motion analysis, as applied to evolutionary biomechanics, has experienced its own evolution over the last 50 years. Here we review how an ever-increasing fossil record, together with continuing advancements in biomechanics techniques, have shaped our understanding of the origin of upright bipedal walking. The original, and long-established hypothesis held by Lamarck (1809), Darwin (1859) and Keith (1934), amongst others, maintained that bipedality originated in an arboreal context.

StW 573 Australopithecus prometheus: Its Significance for an Australopith Bauplan.

The StW 573 skeleton of Australopithecus prometheus from Sterkfontein Member 2 is some 93% complete and thus by far the most complete member of that genus yet found. Firmly dated at 3.67 Ma, it is one of the earliest specimens of its genus.

Keep your head down: Maintaining gait stability in challenging conditions.

Background: Peripheral vision often deteriorates with age, disrupting our ability to maintain normal locomotion. Laboratory based studies have shown that lower visual field loss, in particular, is associated with changes in gaze and gait behaviour whilst walking and this, in turn, increases the risk of falling in the elderly. Separately, gaze and gait behaviours change and fall risk increases when walking over complex surfaces.

Physical and perceptual measures of walking surface complexity strongly predict gait and gaze behaviour.

Background: Walking surfaces vary in complexity and are known to affect stability and fall risk whilst walking. However, existing studies define surfaces through descriptions only.

Objective: This study used a multimethod approach to measure surface complexity in order to try to characterise surfaces with respect to locomotor stability.

Look out: an exploratory study assessing how gaze (eye angle and head angle) and gait speed are influenced by surface complexity.

Background: Most research investigating the connection between walking and visual behaviour has assessed only eye movements (not head orientation) in respect to locomotion over smooth surfaces in a laboratory. This is unlikely to reflect gaze changes found over the complex surfaces experienced in the real world, especially given that eye and head movements have rarely been assessed simultaneously.

Research Question: How does gaze (eye and head) angle and gait speed change when walking over surfaces of different complexity?

Methods: In this exploratory study, we used a mobile eye tracker to monitor eye movements and inertia measurement unit sensors (IMUs) to measure head angle whilst subjects ( = 11) walked over surfaces with different complexities both indoors and outdoors.

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism.

Functional morphology of the atlas reflects multiple aspects of an organism's biology. More specifically, its shape indicates patterns of head mobility, while the size of its vascular foramina reflects blood flow to the brain. Anatomy and function of the early hominin atlas, and thus, its evolutionary history, are poorly documented because of a paucity of fossilized material.

The long limb bones of the StW 573 Australopithecus skeleton from Sterkfontein Member 2: Descriptions and proportions.

Due to its completeness, the A.L. 288-1 ('Lucy') skeleton has long served as the archetypal bipedal Australopithecus.

A Three-Dimensional Musculoskeletal Model of the Western Lowland Gorilla Foot: Examining Muscle Torques and Function.

Due to difficulty of obtaining accurate quantitative data on foot muscles, relatively little has been done to study foot muscle function in non-human apes. Gorilla feet are known to be similar in bony proportions and mechanics to those of humans, hence are key to understanding human foot evolution and its ecological context. We present the first 3D musculoskeletal computer model of a western lowland gorilla foot, giving muscle torques about the tarsometatarsal, metatarsophalangeal and interphalangeal joints of digits 2-5.

A 3D musculoskeletal model of the western lowland gorilla hind limb: moment arms and torque of the hip, knee and ankle.

Three-dimensional musculoskeletal models have become increasingly common for investigating muscle moment arms in studies of vertebrate locomotion. In this study we present the first musculoskeletal model of a western lowland gorilla hind limb. Moment arms of individual muscles around the hip, knee and ankle were compared with previously published data derived from the experimental tendon travel method.

Practice makes perfect: Performance optimisation in 'arboreal' parkour athletes illuminates the evolutionary ecology of great ape anatomy.

An animal's size is central to its ecology, yet remarkably little is known about the selective pressures that drive this trait. A particularly compelling example is how ancestral apes evolved large body mass in such a physically and energetically challenging environment as the forest canopy, where weight-bearing branches and lianas are flexible, irregular and discontinuous, and the majority of preferred foods are situated on the most flexible branches at the periphery of tree crowns. To date the issue has been intractable due to a lack of relevant fossil material, the limited capacity of the fossil record to reconstruct an animal's behavioural ecology and the inability to measure energy consumption in freely moving apes.

The nature of functional variability in plantar pressure during a range of controlled walking speeds.

During walking, variability in step parameters allows the body to adapt to changes in substrate or unexpected perturbations that may occur as the feet interface with the environment. Despite a rich literature describing biomechanical variability in step parameters, there are as yet no studies that consider variability at the body-environment interface. Here, we used pedobarographic statistical parametric mapping (pSPM) and two standard measures of variability, mean square error (m.

The hominins: a very conservative tribe? Last common ancestors, plasticity and ecomorphology in Hominidae. Or, What's in a name?

In the early 20th century the dominant paradigm for the ecological context of the origins of human bipedalism was arboreal suspension. In the 1960s, however, with recognition of the close genetic relationship of humans, chimpanzees and bonobos, and with the first field studies of mountain gorillas and common chimpanzees, it was assumed that locomotion similar to that of common chimpanzees and mountain gorillas, which appeared to be dominated by terrestrial knuckle-walking, must have given rise to human bipedality. This paradigm has been popular, if not universally dominant, until very recently.

Locomotor Ecology of Propithecus verreauxi in Kirindy Mitea National Park.

The locomotor behaviour of 2 groups of Propithecus verreauxi (Verreaux's sifaka) was studied over an 8-month period in Kirindy Mitea National Park (KMNP), Madagascar. This paper assesses the major characteristics of their locomotion, focusing on the extent that seasonal variation in climate and habitat, and local variation in habitat, is reflected in changes in locomotor behaviour. P.

Locomotor flexibility in Lepilemur explained by habitat and biomechanics.

There are at present few comparable studies of lemur locomotion in the wild. This has unfortunately meant we have little knowledge about locomotor variation, and hence flexibility, with regard to differences in support availability and habitat structure. Here we compare the locomotion of Lepilemur edwardsi at Ankarafantsika with that of Lepilemur ruficaudatus at Kirindy-Mitea National Park.

Analysis of joint force and torque for the human and non-human ape foot during bipedal walking with implications for the evolution of the foot.

The feet of apes have a different morphology from those of humans. Until now, it has merely been assumed that the morphology seen in humans must be adaptive for habitual bipedal walking, as the habitual use of bipedal walking is generally regarded as one of the most clear-cut differences between humans and apes. This study asks simply whether human skeletal proportions do actually enhance foot performance during human-like bipedalism, by examining the influence of foot proportions on force, torque and work in the foot joints during simulated bipedal walking.

Vector field statistics for objective center-of-pressure trajectory analysis during gait, with evidence of scalar sensitivity to small coordinate system rotations.

Center of pressure (COP) trajectories summarize the complex mechanical interaction between the foot and a contacted surface. Each trajectory itself is also complex, comprising hundreds of instantaneous vectors over the duration of stance phase. To simplify statistical analysis often a small number of scalars are extracted from each COP trajectory.

The evolution of compliance in the human lateral mid-foot.

Fossil evidence for longitudinal arches in the foot is frequently used to constrain the origins of terrestrial bipedality in human ancestors. This approach rests on the prevailing concept that human feet are unique in functioning with a relatively stiff lateral mid-foot, lacking the significant flexion and high plantar pressures present in non-human apes. This paradigm has stood for more than 70 years but has yet to be tested objectively with quantitative data.

Factors affecting the compliance and sway properties of tree branches used by the Sumatran orangutan (Pongo abelii).

The tropical arboreal environment is a mechanically complex and varied habitat. Arboreal inhabitants must adapt to changes in the compliance and stability of supports when moving around trees. Because the orangutan is the largest habitual arboreal inhabitant, it is unusually susceptible to branch compliance and stability and therefore represents a unique animal model to help investigate how animals cope with the mechanical heterogeneity of the tropical canopy.

Holocene footprints in Namibia: the influence of substrate on footprint variability.

We report a Holocene human and animal footprint site from the Namib Sand Sea, south of Walvis Bay, Namibia. Using these data, we explore intratrail footprint variability associated with small variations in substrate properties using a "whole foot" analytical technique developed for the studies in human ichnology. We demonstrate high levels of intratrail variability as a result of variations in grain size, depositional moisture content, and the degree of sediment disturbance, all of which determine the bearing capacity of the substrate.

Preserving the impossible: conservation of soft-sediment hominin footprint sites and strategies for three-dimensional digital data capture.

Human footprints provide some of the most publically emotive and tangible evidence of our ancestors. To the scientific community they provide evidence of stature, presence, behaviour and in the case of early hominins potential evidence with respect to the evolution of gait. While rare in the geological record the number of footprint sites has increased in recent years along with the analytical tools available for their study.

Short-term step-to-step correlation in plantar pressure distributions during treadmill walking, and implications for footprint trail analysis.

The gait cycle is continuous, but for practical reasons one is often forced to analyze one or only a few adjacent cycles, for example in non-treadmill laboratory investigations and in fossilized footprint analysis. The nature of variability in long-term gait cycle dynamics has been well-investigated, but short-term variability, and specifically correlation, which are highly relevant to short gait bouts, have not. We presently tested for step-to-step autocorrelation in a total of 5243 plantar pressure (PP) distributions from ten subjects who walked at 1.

Nest-building orangutans demonstrate engineering know-how to produce safe, comfortable beds.

Nest-building orangutans must daily build safe and comfortable nest structures in the forest canopy and do this quickly and effectively using the branches that surround them. This study aimed to investigate the mechanical design and architecture of orangutan nests and determine the degree of technical sophistication used in their construction. We measured the whole nest compliance and the thickness of the branches used and recorded the ways in which the branches were fractured.

Functional adaptations in the forelimb muscles of non-human great apes.

The maximum capability of a muscle can be estimated from simple measurements of muscle architecture such as muscle belly mass, fascicle length and physiological cross-sectional area. While the hindlimb anatomy of the non-human apes has been studied in some detail, a comparative study of the forelimb architecture across a number of species has never been undertaken. Here we present data from chimpanzees, bonobos, gorillas and an orangutan to ascertain if, and where, there are functional differences relating to their different locomotor repertoires and habitat usage.

The extraordinary athletic performance of leaping gibbons.

The distance that animals leap depends on their take-off angle and velocity. The velocity is generated solely by mechanical work during the push-off phase of standing-start leaps. Gibbons are capable of exceptional leaping performance, crossing gaps in the forest canopy exceeding 10 m, yet possess none of the adaptations possessed by specialist leapers synonymous with maximizing mechanical work.

Human-like external function of the foot, and fully upright gait, confirmed in the 3.66 million year old Laetoli hominin footprints by topographic statistics, experimental footprint-formation and computer simulation.

It is commonly held that the major functional features of the human foot (e.g. a functional longitudinal medial arch, lateral to medial force transfer and hallucal (big-toe) push-off) appear only in the last 2 Myr, but functional interpretations of footbones and footprints of early human ancestors (hominins) prior to 2 million years ago (Mya) remain contradictory.