Energetics of running: a new perspective

Abstract

The amount of energy used to run a mile is nearly the same whether it is run at top speed or at a leisurely pace (although it is used more rapidly at the higher speed). This puzzling independence of energy cost and speed is found generally among running animals, although, on a per gram basis, cost is much higher for smaller animals. Running involves little work against the environment; work is done by muscles and tendons to lift and accelerate the body and limbs. Some of the work is recovered from muscle-tendon springs without metabolic cost and work rate does not parallel metabolic rate with either speed or size. Regardless of the amount of work muscles do, they must be activated and develop force to support the weight of the body. Load-carrying experiments have shown that the cost of supporting an extra newton of load is the same as the weight-specific cost of running. Size differences in cost are proportional to stride frequency at equivalent speeds, suggesting that the time available for developing force is important in determining cost. We report a simple inverse relationship between the rate of energy used for running and the time the foot applies force to the ground during each stride. These results support the hypothesis that it is primarily the cost of supporting the animal's weight and the time course of generating this force that determines the cost of running.

Differences in leg muscle activity during running and cycling in humans

“…Roberts et al (1997), however, showed that in the gastrocnemius muscle of turkeys who ran on the level, no stretch of the contractile elements occurred. Furthermore, Kram and Taylor (1990) based their cost-ofgenerating-force hypothesis on the idea that during level running the contractile elements of the muscle operate isometrically. Therefore, assuming that during running on the level, as well as up inclines, in the stretching phase no stretch of the contractile elements takes place, it is likely that in both running situations (level and inclination) storage and re-utilization of elastic energy plays a role.…”

An analytical estimation of the energy cost for legged locomotion

“…The decrease in the duty ratio also implies a decrease in the average number of legs that contact the ground. (2) Stride length, which is the forward distance the body moves within the stride period, and stance length, the forward distance in a stance duration, increase slightly with locomotion speed or remain almost constant [4,8,9,12,[15][16][17]. They begin to increase when the stride period become almost constant [2,12].…”

“…(4) The metabolic cost per unit time linearly increases with locomotion speed. Hence, the cost of transport, which is the metabolic cost for moving a unit mass by a unit distance, decreases with speed and becomes almost constant in a wide region of locomotion speed [1,3,6,15,[22][23][24][25][26][27][28][29].…”

The apparently contradictory energetics of hopping and running: the counter-intuitive effect of constraints resolves the paradox

“…Kram and Taylor (1990) formulated a general cost function for running based on the hypothesis that 'it is primarily the cost of supporting the animal's weight and the time course of generating this force that determines the cost of running'. They assumed that during constant-velocity running, a substantial amount of mechanical energy could be stored and returned elastically by tendons so muscles would only need to do a small amount of work to lift and accelerate the body and limbs from stride to stride (Alexander, 1984;Ker et al, 1987).…”

“…Developing greater force or using faster fibers to develop a given amount of force more quickly would increase the amount of energy used (Rall, 1985;Heglund and Cavagna, 1987). Thus, Kram and Taylor (1990) predicted that 'the rate of energy consumed by the muscles of a running animal per newton of body weight ( _ E metab =W b ) is inversely proportional to the weight-specific rate of force application, W b /t c divided by W b , where t c is the time for which the foot applies force to the ground during each stride…where c is a cost coefficient', such that:…”