Person: Holowka, Nicholas
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Holowka
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Nicholas
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Holowka, Nicholas
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Publication Foot Callus Thickness Does Not Trade Off Protection for Tactile Sensitivity During Walking(Springer Science and Business Media LLC, 2019-06-26) Holowka, Nicholas; Wynands, Bert; Drechsel, Tina; Yegian, Andrew; Tobolsky, Victoria; Okutoyi, Paul; Mang’eni Ojiambo, Robert; Halle, Diresibachew; Sigel, Timothy; Zippenfennig, Claudio; Milani, Thomas; Lieberman, DanielUntil relatively recently, humans, like other animals, were habitually barefoot, hence the soles of our feet were the only direct contact between the body and the ground when walking. There is indirect evidence that simple footwear such as sandals and moccasins were first invented within the last 40 Ka, the oldest recovered footwear dates to 8 Ka, and inexpensive shoes with cushioned heels were not developed until the Industrial Revolution3. Because calluses, thickened and hardened areas of the epidermal layer of the skin, are the evolutionary solution to protecting the foot, we wondered if they differ from shoes in maintaining tactile sensitivity during walking, especially at initial foot contact to improve safety on surfaces that can be slippery, abrasive or otherwise injurious or uncomfortable. Here we show that, as expected, people from Kenya and the United States who frequently walk barefoot have thicker and harder calluses than those who typically use footwear. However, in contrast to shoes, callus thickness does not trade-off protection, measured as hardness and stiffness, for the ability to perceive tactile stimuli at frequencies experienced during walking. Additionally, unlike cushioned footwear, callus thickness does not affect how hard people’s feet strike the ground during walking, as indicated by impact forces. Along with providing protection and comfort at the cost of tactile sensitivity, cushioned footwear also lowers rates of loading at impact but increases force impulses, with unknown effects on the skeleton that merit future study.Publication Heel impact forces during barefoot versus minimally shod walking among Tarahumara subsistence farmers and urban Americans(The Royal Society Publishing, 2018) Wallace, Ian; Koch, Elizabeth; Holowka, Nicholas; Lieberman, DanielDespite substantial recent interest in walking barefoot and in minimal footwear, little is known about potential differences in walking biomechanics when unshod versus minimally shod. To test the hypothesis that heel impact forces are similar during barefoot and minimally shod walking, we analysed ground reaction forces recorded in both conditions with a pedography platform among indigenous subsistence farmers, the Tarahumara of Mexico, who habitually wear minimal sandals, as well as among urban Americans wearing commercially available minimal sandals. Among both the Tarahumara (n = 35) and Americans (n = 30), impact peaks generated in sandals had significantly (p < 0.05) higher force magnitudes, slower loading rates and larger vertical impulses than during barefoot walking. These kinetic differences were partly due to individuals' significantly greater effective mass when walking in sandals. Our results indicate that, in general, people tread more lightly when walking barefoot than in minimal footwear. Further research is needed to test if the variations in impact peaks generated by walking barefoot or in minimal shoes have consequences for musculoskeletal health.Publication Foot strength and stiffness are related to footwear use in a comparison of minimally- vs. conventionally-shod populations(Nature Publishing Group UK, 2018) Holowka, Nicholas; Wallace, Ian; Lieberman, DanielThe longitudinal arch (LA) helps stiffen the foot during walking, but many people in developed countries suffer from flat foot, a condition characterized by reduced LA stiffness that can impair gait. Studies have found this condition is rare in people who are habitually barefoot or wear minimal shoes compared to people who wear conventional modern shoes, but the basis for this difference remains unknown. Here we test the hypothesis that the use of shoes with features that restrict foot motion (e.g. arch supports, toe boxes) is associated with weaker foot muscles and reduced foot stiffness. We collected data from minimally-shod men from northwestern Mexico and men from urban/suburban areas in the United States who wear ‘conventional’ shoes. We measured dynamic LA stiffness during walking using kinematic and kinetic data, and the cross-sectional areas of three intrinsic foot muscles using ultrasound. Compared to conventionally-shod individuals, minimally-shod individuals had higher and stiffer LAs, and larger abductor hallucis and abductor digiti minimi muscles. Additionally, abductor hallucis size was positively associated with LA stiffness during walking. Our results suggest that use of conventional modern shoes is associated with weaker intrinsic foot muscles that may predispose individuals to reduced foot stiffness and potentially flat foot.Publication Form and function of the human and chimpanzee forefoot: implications for early hominin bipedalism(Nature Publishing Group, 2016) Fernández, Peter J.; Holowka, Nicholas; Demes, Brigitte; Jungers, William L.During bipedal walking, modern humans dorsiflex their forefoot at the metatarsophalangeal joints (MTPJs) prior to push off, which tightens the plantar soft tissues to convert the foot into a stiff propulsive lever. Particular features of metatarsal head morphology such as “dorsal doming” are thought to facilitate this stiffening mechanism. In contrast, chimpanzees are believed to possess MTPJ morphology that precludes high dorsiflexion excursions during terrestrial locomotion. The morphological affinity of the metatarsal heads has been used to reconstruct locomotor behavior in fossil hominins, but few studies have provided detailed empirical data to validate the assumed link between morphology and function at the MTPJs. Using three-dimensional kinematic and morphometric analyses, we show that humans push off with greater peak dorsiflexion angles at all MTPJs than do chimpanzees during bipedal and quadrupedal walking, with the greatest disparity occurring at MTPJ 1. Among MTPJs 2–5, both species exhibit decreasing peak angles from medial to lateral. This kinematic pattern is mirrored in the morphometric analyses of metatarsal head shape. Analyses of Australopithecus afarensis metatarsals reveal morphology intermediate between humans and chimpanzees, suggesting that this species used different bipedal push-off kinematics than modern humans, perhaps resulting in a less efficient form of bipedalism.