The metabolic cost of walking in humans, chimpanzees, and early hominins

Washington University, Department of Anthropology, St. Louis, MO 63130, USA.
Journal of Human Evolution (Impact Factor: 3.73). 12/2008; 56(1):43-54. DOI: 10.1016/j.jhevol.2008.09.001
Source: PubMed


Bipedalism is a defining feature of the hominin lineage, but the nature and efficiency of early hominin walking remains the focus of much debate. Here, we investigate walking cost in early hominins using experimental data from humans and chimpanzees. We use gait and energetics data from humans, and from chimpanzees walking bipedally and quadrupedally, to test a new model linking locomotor anatomy and posture to walking cost. We then use this model to reconstruct locomotor cost for early, ape-like hominins and for the A.L. 288 Australopithecus afarensis specimen. Results of the model indicate that hind limb length, posture (effective mechanical advantage), and muscle fascicle length contribute nearly equally to differences in walking cost between humans and chimpanzees. Further, relatively small changes in these variables would decrease the cost of bipedalism in an early chimpanzee-like biped below that of quadrupedal apes. Estimates of walking cost in A.L. 288, over a range of hypothetical postures from crouched to fully extended, are below those of quadrupedal apes, but above those of modern humans. These results indicate that walking cost in early hominins was likely similar to or below that of their quadrupedal ape-like forebears, and that by the mid-Pliocene, hominin walking was less costly than that of other apes. This supports the hypothesis that locomotor energy economy was an important evolutionary pressure on hominin bipedalism.

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Available from: Herman Pontzer
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    • "Humans are decidedly the outlier among catarrhine primates, having relatively short arms and long legs relative to each other and to trunk length. This unique pattern primarily reflects selection for bipedalism on hindlimb length (Bramble and Lieberman, 2004; Sockol et al., 2007; Pontzer et al., 2009), but also potentially selection for shorter forelimb elements in the Homo, perhaps due to demands associated with increased tool use and manipulation and/or reduced reliance on arboreal behaviors. "
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    ABSTRACT: Understanding the forces that have influenced the evolution of shape, size, and proportions of the human appendages, including both limbs and girdles (scapula and pelvis), have played an important part in paleoanthropology. This chapter outlines a framework to address evolutionary variation in the human appendages, specifically regarding key transitions from the last common ancestor (LCA) of chimpanzees and modern humans, which combines data from extant comparative models and fossil hominins to generate testable developmental hypotheses. For the scapula, pelvis, and then limbs, the chapter first describes the relevant skeletal anatomy and development, and then briefly discusses the tissues, signaling centers, and genes currently known to be involved in their morphogenesis. The chapter compares phenotypic variation in each element in a morphospace. It utilizes the idea that evolutionary trajectories through morphospace represent developmental transformations from putative ancestral morphotypes to living species.
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    • "There is good empirical evidence that activated muscle volume relates closely to metabolic cost for level legged locomotion, and that metabolic cost minimisation is effective in accounting for a broad range of gait features (see Bertram and Ruina, 2001; Donelan et al., 2001). 'Cost of force' models have been applied to a range of animals at a range of speeds, and are highly effective at relating metabolic costs to the costs of activating muscle to impose (or oppose) forces (Taylor, 1985; Kram and Taylor, 1990; Roberts et al., 1998; Doke and Kuo, 2007; Pontzer et al., 2009). Furthermore, there is a good mechanistic account for why muscle activation might be metabolically energetic: there are considerable, measurable costs associated with simply pumping ions in and out of muscle in order to start and stop a contraction (Barclay, 2012). "
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    ABSTRACT: Terrestrial locomotion on legs is energetically expensive. Compared with cycling, or with locomotion in swimming or flying animals, walking and running are highly uneconomical. Legged gaits that minimise mechanical work have previously been identified and broadly match walking and running at appropriate speeds. Furthermore, the 'cost of muscle force' approaches are effective in relating locomotion kinetics to metabolic cost. However, few accounts have been made for why animals deviate from either work-minimising or muscle-force-minimising strategies. Also, there is no current mechanistic account for the scaling of locomotion kinetics with animal size and speed. Here, we report measurements of ground reaction forces in walking children and adult humans, and their stance durations during running. We find that many aspects of gait kinetics and kinematics scale with speed and size in a manner that is consistent with minimising muscle activation required for the more demanding between mechanical work and power: spreading the duration of muscle action reduces activation requirements for power, at the cost of greater work demands. Mechanical work is relatively more demanding for larger bipeds - adult humans - accounting for their symmetrical M-shaped vertical force traces in walking, and relatively brief stance durations in running compared with smaller bipeds - children. The gaits of small children, and the greater deviation of their mechanics from work-minimising strategies, may be understood as appropriate for their scale, not merely as immature, incompletely developed and energetically sub-optimal versions of adult gaits.
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    • "Although the selective factors underlying the evolution of both walking and running are debated, it is likely that locomotor economy played a key role. Hypothesized energysaving features for walking include long legs and dorsally oriented ischia (Crompton et al., 1998; Pontzer et al., 2009; Robinson, 1972; Sockol et al., 2007). Energy saving features for running in the genus Homo include a long, compliant Achilles tendon and a spring-like median longitudinal arch, which are known to store and recover elastic energy during running in other vertebrates (Biewener, 2003; Ker et al., 1987; Roberts, 2002). "
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    ABSTRACT: The human iliotibial band (ITB) is a poorly understood fascial structure that may contribute to energy savings during locomotion. This study evaluated the capacity of the ITB to store and release elastic energy during running, at speeds ranging from 2-5m/s, using a model that characterizes the three-dimensional musculoskeletal geometry of the human lower limb and the force-length properties of the ITB, tensor fascia lata (TFL), and gluteus maximus (GMax). The model was based on detailed analyses of muscle architecture, dissections of 3-D anatomy, and measurements of the muscles' moment arms about the hip and knee in five cadaveric specimens. The model was used, in combination with measured joint kinematics and published EMG recordings, to estimate the forces and corresponding strains in the ITB during running. We found that forces generated by TFL and GMax during running stretch the ITB substantially, resulting in energy storage. Anterior and posterior regions of the ITB muscle-tendon units (MTUs) show distinct length change patterns, in part due to different moment arms at the hip and knee. The posterior ITB MTU likely stores more energy than the anterior ITB MTU because it transmits larger muscle forces. We estimate that the ITB stores about 1J of energy per stride during slow running and 7J during fast running, which represents approximately 14% of the energy stored in the Achilles tendon at a comparable speed. This previously unrecognized mechanism for storing elastic energy may be an adaptation to increase human locomotor economy. Copyright © 2015 Elsevier Ltd. All rights reserved.
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