Roshna E. Wunderlich

Gender differences in adult foot shape: implications for shoe design.

PURPOSE To analyze gender differences in foot shape in a large sample of young individuals. METHODS Univariate t-tests and multivariate discriminant analyses were used to assess 1) significant differences between men and women for each foot and leg dimension, standardized to foot length, 2) the reliability of classification into gender classes using the absolute and standardized variable sets, and 3) the relative importance of each variable to the discrimination between men and women. RESULTS Men have longer and broader feet than women for a given stature. After normalization of the measurements by foot length, men and women were found to differ significantly in two calf, five ankle, and four foot shape variables. Classification by gender using absolute values was correct at least 93% of the time. Using the variables standardized to foot length, gender was correctly classified 85% of the time. CONCLUSIONS This study demonstrates that female feet and legs are not simply scaled-down versions of male feet but rather differ in a number of shape characteristics, particularly at the arch, the lateral side of the foot, the first toe, and the ball of the foot. These differences should be taken into account in the design and manufacture of womens sport shoes.

Ecomorphology and Behavior of Giant Extinct Lemurs from Madagascar

Inferring the behavior of extinct organisms is a formidable task, even under the best of circumstances (Rudwick, 1964; Stern and Susman, 1983; Kay, 1984; Thomason, 1995). Nevertheless, and in spite of inevitable complications and limitations, such inferences remain the ultimate goal of paleobiologists if we are to understand fossils as integrated organisms rather than isolated bones and atomized character states. In this chapter we attempt to breathe life back into the osteological remains of recently extinct (or “subfossil”) prosimian primates from the Quaternary of Madagascar. Subfossil lemurs provide many special opportunities to the optimistic functional morphologist, but they also present their own unusual set of complications and potential frustrations. Approximately one-third of Madagascar’s known primate species were driven to extinction in the late Holocene by the lethal interaction of aridification and human colonization (Burney, 1997; Dewar, 1997; Simons, 1997), including all taxa of large body size (> 9 kg). Two new extinct species from northern Madagascar (Babakotia radofilai and Mesopropithecus dolichobrachion) have been discovered and described in the last decade (Godfrey et al., 1990; Simons et al., 1995), and a third new species from the northwest will be diagnosed soon (Jungers et al., in prep.). Sixteen currently recognized subfossil species of Malagasy primates are represented in museum collections, most by numerous individuals, including a growing tally of specimens with associated craniodental and postcranial elements (e.g., MacPhee et al., 1984; Simons et al., 1992,Simons et al., 1995; Wunderlich et al., 1996). Table I summarizes the current taxonomy of the extinct lemurs. Aspects of morphology suggest that cheirogaleids are more closely related to galagos and lorises than to other Malagasy primates (Szalay and Katz, 1973; Cartmill, 1975; Schwartz and Tattersall, 1985; Yoder, 1992). Molecular results, as well as “total evidence” analyses that combine morphological and molecular data, argue instead that the Malagasy primates are probably monophyletic (Yoder, 1994,Yoder, 1996). Regardless of the placement of the cheirogaleids within strepsirrhines, the precise relationships among the various ancient clades of Malagasy primates remain somewhat fuzzy, even from a biomolecular perspective (Yoder, 1997; Yoderet al., 1999).

Variation in Foot Strike Patterns during Running among Habitually Barefoot Populations

Endurance running may have a long evolutionary history in the hominin clade but it was not until very recently that humans ran wearing shoes. Research on modern habitually unshod runners has suggested that they utilize a different biomechanical strategy than runners who wear shoes, namely that barefoot runners typically use a forefoot strike in order to avoid generating the high impact forces that would be experienced if they were to strike the ground with their heels first. This finding suggests that our habitually unshod ancestors may have run in a similar way. However, this research was conducted on a single population and we know little about variation in running form among habitually barefoot people, including the effects of running speed, which has been shown to affect strike patterns in shod runners. Here, we present the results of our investigation into the selection of running foot strike patterns among another modern habitually unshod group, the Daasanach of northern Kenya. Data were collected from 38 consenting adults as they ran along a trackway with a plantar pressure pad placed midway along its length. Subjects ran at self-selected endurance running and sprinting speeds. Our data support the hypothesis that a forefoot strike reduces the magnitude of impact loading, but the majority of subjects instead used a rearfoot strike at endurance running speeds. Their percentages of midfoot and forefoot strikes increased significantly with speed. These results indicate that not all habitually barefoot people prefer running with a forefoot strike, and suggest that other factors such as running speed, training level, substrate mechanical properties, running distance, and running frequency, influence the selection of foot strike patterns.

Dynamic Pressure Patterns in the Hands of Olive Baboons (Papio anubis) During Terrestrial Locomotion: Implications for Cercopithecoid Primate Hand Morphology

Habitually terrestrial monkeys adopt digitigrade hand postures at slow speeds to increase effective forelimb length and reduce distal limb joint moments. As these primates move faster, however, their hands transition to a more palmigrade posture, which is likely associated with the inability of wrist and hand joints to resist higher ground reaction forces (GRF) associated with faster speeds. Transitioning to a palmigrade posture may serve to distribute GRFs over a larger surface area (i.e., increased palmar contact), ultimately reducing stresses in fragile hand bones. To test this hypothesis, dynamic palmar pressure data were collected on two adult baboons (Papio anubis) walking, running, and galloping across a runway integrated with a dynamic pressure mat (20 steps each; speed range: 0.46–4.0 m/s). Peak GRF, contact area, peak pressure, and pressure‐time integral were quantified in two regions of the hand: fingers and palms (including metacarpal heads). At slower speeds with lower GRFs, the baboons use digitigrade postures resulting in small palmar contact area (largely across the metacarpal heads). At faster speeds with higher GRFs, they used less digitigrade hand postures resulting in increased palmar contact area. Finger contact area did not change across speeds. Despite higher GRFs at faster speeds, metacarpal pressure was moderated across speeds due to increased palmar contact area as animals transitioned from digitigrady to palmigrady. In contrast, the pressure in the fingers increased with faster speeds. Results indicate that the transition from digitigrady to palmigrady distributes increased forces over a larger palmar surface area. Such dynamic changes in palmar pressure likely moderate strain in the gracile bones of the hand, a structure that is integral not only for locomotion, but also feeding and social behaviors in primates. Anat Rec, 293:710–718, 2010.

Hand and foot pressures in the aye-aye (Daubentonia madagascariensis) reveal novel biomechanical trade-offs required for walking on gracile digits.

SUMMARY Arboreal animals with prehensile hands must balance the complex demands of bone strength, grasping and manipulation. An informative example of this problem is that of the aye-aye (Daubentonia madagascariensis), a rare lemuriform primate that is unusual in having exceptionally long, gracile fingers specialized for foraging. In addition, they are among the largest primates to engage in head-first descent on arboreal supports, a posture that should increase loads on their gracile digits. We test the hypothesis that aye-ayes will reduce pressure on their digits during locomotion by curling their fingers off the substrate. This hypothesis was tested using simultaneous videographic and pressure analysis of the hand, foot and digits for five adult aye-ayes during horizontal locomotion and during ascent and descent on a 30° instrumented runway. Aye-ayes consistently curled their fingers during locomotion on all slopes. When the digits were in contact with the substrate, pressures were negligible and significantly less than those experienced by the palm or pedal digits. In addition, aye-ayes lifted their hands vertically off the substrate instead of ‘toeing-off’ and descended head-first at significantly slower speeds than on other slopes. Pressure on the hand increased during head-first descent relative to horizontal locomotion but not as much as the pressure increased on the foot during ascent. This distribution of pressure suggests that aye-ayes shift their weight posteriorly during head-first descent to reduce loads on their gracile fingers. This research demonstrates several novel biomechanical trade-offs to deal with complex functional demands on the mammalian skeleton.

Footprints reveal direct evidence of group behavior and locomotion in Homo erectus

Bipedalism is a defining feature of the human lineage. Despite evidence that walking on two feet dates back 6–7 Ma, reconstructing hominin gait evolution is complicated by a sparse fossil record and challenges in inferring biomechanical patterns from isolated and fragmentary bones. Similarly, patterns of social behavior that distinguish modern humans from other living primates likely played significant roles in our evolution, but it is exceedingly difficult to understand the social behaviors of fossil hominins directly from fossil data. Footprints preserve direct records of gait biomechanics and behavior but they have been rare in the early human fossil record. Here we present analyses of an unprecedented discovery of 1.5-million-year-old footprint assemblages, produced by 20+ Homo erectus individuals. These footprints provide the oldest direct evidence for modern human-like weight transfer and confirm the presence of an energy-saving longitudinally arched foot in H. erectus. Further, print size analyses suggest that these H. erectus individuals lived and moved in cooperative multi-male groups, offering direct evidence consistent with human-like social behaviors in H. erectus.

Interpreting locomotor biomechanics from the morphology of human footprints.

Fossil hominin footprints offer unique direct windows to the locomotor behaviors of our ancestors. These data could allow a clearer understanding of the evolution of human locomotion by circumventing issues associated with indirect interpretations of habitual locomotor patterns from fossil skeletal material. However, before we can use fossil hominin footprints to understand better the evolution of human locomotion, we must first develop an understanding of how locomotor biomechanics are preserved in, and can be inferred from, footprint morphologies. In this experimental study, 41 habitually barefoot modern humans created footprints under controlled conditions in which variables related to locomotor biomechanics could be quantified. Measurements of regional topography (depth) were taken from 3D models of those footprints, and principal components analysis was used to identify orthogonal axes that described the largest proportions of topographic variance within the human experimental sample. Linear mixed effects models were used to quantify the influences of biomechanical variables on the first five principal axes of footprint topographic variation, thus providing new information on the biomechanical variables most evidently expressed in the morphology of human footprints. The footprints overall depth was considered as a confounding variable, since biomechanics may be linked to the extent to which a substrate deforms. Three of five axes showed statistically significant relationships with variables related to both locomotor biomechanics and substrate displacement; one axis was influenced only by biomechanics and another only by the overall depth of the footprint. Principal axes of footprint morphological variation were significantly related to gait type (walking or running), kinematics of the hip and ankle joints and the distribution of pressure beneath the foot. These results provide the first quantitative framework for developing hypotheses regarding the biomechanical patterns reflected by fossil hominin footprints by demonstrating the statistically significant effects of specific kinematic variables on patterns of variation in footprint topography.

Foot use during vertical climbing in chimpanzees (Pan troglodytes)

Upright bipedalism is a hallmark of hominin locomotion, however debates continue regarding the extent of arboreal locomotion and the nature of bipedalism practiced by early hominins. Pedal form and function play a prominent role in these debates, as the foot is the element that directly interacts with the locomotor substrate. Recent finds have substantially increased the availability of associated foot remains of early hominins and emphasized the enigmatic nature of the early evolution of human bipedalism. New discoveries of associated forefoot remains have afforded the opportunity to assess relative proportions across the forefoot of fossil hominins and illuminated the need for data on relative loading across the forefoot in extant hominoids. In order to provide functional data with which to examine the relationship between bony features and load distribution across the forefoot during climbing, we present the first analysis of plantar pressure distribution across the forefoot of chimpanzees climbing a vertical support. Chimpanzees load the medial metatarsals and first toe disproportionately during vertical climbing. Peak pressures on these elements occur at the end of stance phase during climbing and are higher than on any other elements of the foot. Toe pressures are considerably higher during vertical climbing than during knuckle-walking or movement on horizontal poles, supporting the notion that the plantarly-broad and dorsally-narrow metatarsal heads in chimpanzees and some early hominins are associated with close-packing of the metatarsophalangeal joint during climbing.

Experimental Research on Hand Use and Function in Primates

The primate hand has long intrigued researchers of different disciplines. The extensive and elegant work of Napier included careful observations about the anatomy and function of the primate hand. While such observations and inferences substantially advanced our understanding of the primate hand, a more complete insight into the function of a complex organ such as the hand requires experimental investigation to illuminate patterns of joint movement, muscle activity, and loads. In the last decades, researchers have collected a wealth of information about hand morphology and function by setting up and conducting laboratory-based experiments. In this chapter, we give a comprehensive overview of the experimental work on the nonhuman primate hand that has been done since Napier’s publications in the 1950s. We discuss the different methods that are being used to study hand function: behavioral studies, kinematics, kinetics, dynamic palmar pressure, electromyography, medical imaging and computer modeling. Ultimately, studies focusing on hand form and function, especially those that include a diversity of extant species and integrate different types of data, will lead to a better understanding of the evolution of the human hand.

Gorilla limb kinematics and hominoid locomotor diversity: Implications for hominin locomotor evolution

Leprosy is one of the few specific infectious diseases that can be studied in bioarchaeology due to its characteristic debilitating and disfiguring skeletal changes. Leprosy has been, and continues to be, one of the most socially stigmatising diseases in history, over-riding all other aspects of social identity for the sufferers and frequently resulting in social exclusion. This study examines the stable isotopic evidence of mobility patterns of children, adolescents, and young adult individuals with the lepromatous form of leprosy in Medieval England (10 th –12 th centuries AD) to assess whether the individuals buried with the disease were non-locals, possibly from further afield. Enamel samples from 19 individuals from the St. Mary Magdalen Leprosy Hospital, Winchester (UK) were selected for strontium ( 87 Sr/ 86 6U DQG R[\JHQ į 18 O) stable isotope analysis based on age at death (<30 years), the presence of bone changes associated with lepromatous leprosy, and the underlying geology of their burial locations. The results from these data indicate that the St. Mary Magdalen Leprosy Hospital received an almost equal mixture of local and non-local individuals from further afield, including early pilgrims. At present, the St. Mary Magdalen Leprosy Hospital is the earliest dedicated leprosaria found within Britain and mobility studies such as these can help elucidate and test some of the broader historical notions and identities associated with the movements of those infected with the disease in Medieval England.