The Foot’s Arch and the Energetics of Human Locomotion

Abstract

The energy-sparing spring theory of the foot’s arch has become central to interpretations of the foot’s mechanical function and evolution. Using a novel insole technique that restricted compression of the foot’s longitudinal arch, this study provides the first direct evidence that arch compression/recoil during locomotion contributes to lowering energy cost. Restricting arch compression near maximally (~80%) during moderate-speed (2.7 ms−1) level running increased metabolic cost by + 6.0% (p < 0.001, d = 0.67; unaffected by foot strike technique). A simple model shows that the metabolic energy saved by the arch is largely explained by the passive-elastic work it supplies that would otherwise be done by active muscle. Both experimental and model data confirm that it is the end-range of arch compression that dictates the energy-saving role of the arch. Restricting arch compression had no effect on the cost of walking or incline running (3°), commensurate with the smaller role of passive-elastic mechanics in these gaits. These findings substantiate the elastic energy-saving role of the longitudinal arch during running, and suggest that arch supports used in some footwear and orthotics may increase the cost of running.

Shoes alter the spring-like function of the human foot during running

“…This finding is in line with the key design features of running shoes that aim to provide support for the LA and reduce strain on plantar soft-tissue structures [50,51]. However, this finding also highlights that running shoes may actually limit the capacity for the foot to store and return energy via elastic mechanisms, owing to a reduction in the magnitude of arch compression and recoil [13]. Recent critiques of modern running footwear have argued that cushioning and support characteristics of the shoe potentially impair foot-spring function, with a likely consequence of reduced activation from muscles that support the arch, leading to their weakness and disuse atrophy [3,29,34].…”

“…The LA compresses during early stance, absorbing mechanical energy as the ground reaction force (GRF) increases. Presumably, the energy absorbed is stored within elastic structures supporting the arch [9,13,14]. In late stance, when GRF decreases, the LA recoils, returning elastic energy to deliver power for propulsion [9].…”

“…Stiffness of the LA is provided by passive ligamentous structures [9,14,15] acting in parallel with the intrinsic foot muscles whose relative contribution is continually adjusted by the central nervous system (CNS) in response to mechanosensory stimuli [10,16]. This elegant arrangement allows the mechanical characteristics of the foot to be rapidly adapted to loading or task demands [10] and is thought to improve the efficiency of human running, returning between 8% and 17% of the mechanical energy required for one stride, via passive mechanisms alone [9,13].…”

Reevaluating the functional implications of Australopithecus afarensis navicular morphology

“…The human foot is uniquely characterized by an energy saving, spring-like longitudinal arch that reflects an adaptation to terrestrial walking and running (Ker et al, 1987;Bramble and Lieberman, 2004;DeSilva and Throckmorton, 2010;Ward et al, 2011;Prang, 2015b;Stearne et al, 2016). The presence of a longitudinal arch is reflected in the geometric relationships among the bones of the human foot and ankle (DeSilva and Throckmorton, 2010;Ward et al, 2011;Prang, 2015b), including the declination of the talar head relative to the plane of the talocrural joint (Day and Wood, 1968;Peeters et al, 2013) and the declination of the calcaneocuboid joint relative to its proximodistal axis (Aiello and Dean, 1990;Prang, 2015b).…”

“…Understanding the evolution of the hominin longitudinal arch and its morphological correlates is necessary because they reflect a predominantly terrestrial adaptation (DeSilva, 2010;Ward et al, 2011;Prang, 2015b) and the ability to save energy during running via longitudinal arch compression and elastic recoil (Ker et al, 1987;Bramble and Lieberman, 2004;Stearne et al, 2016). The discovery of postcranial fossils attributed to the Plio-Pleistocene hominin taxon Australopithecus afarensis Latimer et al, 1982) started a crucial debate regarding the roles of arboreality and terrestriality in the locomotor repertoire of early hominins (e.g., Stern and Susman, 1983;Susman et al, 1984) and their evolutionary importance (sensu Latimer, 1991; reviewed by Stern, 2000 andWard, 2002).…”