Energetics and Mechanics of Terrestrial Locomotion

Abstract

This review addresses a simple question: How do muscles use the energy they consume during terrestrial locomotion? Using a comparative approach, it was found that the mass-specific rate of metabolic energy consumption changes by more than ten-fold with body size, while the mass-specific rate at which the muscles performed mechanical work did not change at all. It was also found that the rate of metabolic energy consumption increased linearly with speed, while the rate at which muscles performed mechanical work increased curvilinearly with speed (oc V1.53). We conclude from these observations that the rate at which animals consume metabolic energy during terrestrial locomotion is not determined by the rate at which their muscles perform mechanical work. Instead, the metabolic cost of generating muscular force over time (integral of F dt) appears to determine the metabolic cost of terrestrial locomotion. The cost of generating force increases with increasing speed and decreases with increasing body size in exactly the same manner as cost of locomotion. It is suggested that the metabolic cost of generating muscular force may be determined by the intrinsic velocity of shortening (i.e proportional to rates at which the cross-bridges between actin and myosin cycle) of the muscle motor units that are active during locomotion. Faster motor units are used both as animals increase speed and in equivalent muscles of smaller animals moving at the same speed. This suggestion is testable and future studies should determine whether or not it explains the higher costs of generating muscular force with increasing speed and decreasing body size.

Energy Cost of Running in an Arctic Fox, <em>Alopex lagopus</em>

“…Post-absorptive metabolic rate during running increased linearly with increasing speed. In July the metabolic rate while running almost fitted general equations predicted for mammals (Taylor et al 1982; equation 2) relating metabolic rate at a constant speed to speed and body weight, while it was up to 20% lower in January (equations 3 and 4).…”

“…Compared to the general formula for the metabolic cost of running in mammals (Taylor et al 1982), the measured values in the Arctic Fox in January were as much as 20% lower, indicating that the Arctic Fox is an energetically efficient runner. Both the metabolic rate during running (Figure 1) and the net cost of running (Table 2) were lower in January compared to July.…”

“…The metabolic cost of running in the herbivorous Svalbard Reindeer (Rangifer tarandus platyrhynchus) is reported to fit the values predicted by the equation of Taylor et al (1982) within 3% (Nilssen et al 1984). Another inhabitant of the Arctic, the carnivorous Polar Bear (Ursus maritimus), is in contrast to the Arctic Fox considered to be an inefficient runner (Hurst et al 1982;Øritsland et al 1976).…”

Characterization of Dynamic Behaviors in a Hexapod Robot

“…Biological studies [4][5][6][7] suggest that the ability to effectively recirculate mechanical energy through spring-mass mechanics confers significant energetic benefits in animals, and that fast biological runners adopt the specific mechanics of the SLIP [28]. RHex-class robots can capture this aspect of animal locomotion and demonstrate energetically efficient locomotion as they can passively embed the SLIP dynamics in carefully tuned open-loop controlled gaits [40].…”

“…Energetics of locomotion has been a major topic for scientific discussions [4][5][6][7][8] and remains to be an active research area for both biologists [9,10] and engineers [11][12][13][14][15]. The need for practical mobility in unstructured environments motivates our interest in legged locomotion.…”