Metabolic cost of generating muscular force in human walking: insights from load-carrying and speed experiments

Abstract

We sought to understand how leg muscle function determines the metabolic cost of walking. We first indirectly assessed the metabolic cost of swinging the legs and then examined the cost of generating muscular force during the stance phase. Four men and four women walked at 0.5, 1.0, 1.5, and 2.0 m/s carrying loads equal to 0, 10, 20, and 30% body mass positioned symmetrically about the waist. The net metabolic rate increased in nearly direct proportion to the external mechanical power during moderate-speed (0.5-1.5 m/s) load carrying, suggesting that the cost of swinging the legs is relatively small. The active muscle volume required to generate force on the ground and the rate of generating this force accounted for >85% of the increase in net metabolic rate across moderate speeds and most loading conditions. Although these factors explained less of the increase in metabolic rate between 1.5 and 2.0 m/s ( approximately 50%), the cost of generating force per unit volume of active muscle [i.e., the cost coefficient (k)] was similar across all conditions [k = 0.11 +/- 0.03 (SD) J/cm3]. These data indicate that, regardless of the work muscles do, the metabolic cost of walking can be largely explained by the cost of generating muscular force during the stance phase.

What explains the trot–gallop transition in small mammals?

“…Some studies have not detected any increase in metabolic rate when carrying loads of 5-10% of body mass (Cooke et al, 1991), whereas others have shown increments in metabolic rate higher and lower than those predicted by Taylor et al's proportionality (e.g. Griffin et al, 2003;Marsh et al, 2006). In our experiments, total metabolic rate (measured as ml·O 2 ·min -1 ) increased 38% with a 20% increment in body mass.…”

The energetic benefits of tendon springs in running: is the reduction of muscle work important?

“…It has been demonstrated that the metabolic cost of terrestrial locomotion can be explained largely by the cost of producing force, rather than by the cost of doing work (Kram and Taylor, 1990). Empirical studies show a good correlation between the cost of force production and metabolic cost (Kram and Taylor, 1990;Griffin et al, 2003;Gabaldón et al, 2008), but this model is challenged by the fact that it ignores the metabolically expensive muscle work, which has been observed in muscles active during running (Carrier et al, 1998;Gillis and Biewener, 2002;Daley and Biewener, 2003;Gillis et al, 2005;McGuigan et al, 2009;Roberts et al, 2007). The finding that the cost of force production is not significantly different in isometric and stretch-shorten cycles suggests that force can be produced for a similar cost under a wider range of conditions than previously assumed, and so may explain how the cost of force production can explain the cost of locomotion, even though some muscles perform work.…”

The mass-specific energy cost of human walking is set by stature

“…Although some investigators have subtracted the metabolic rate measured during quiet standing for this purpose, we subtracted basal rather than standing metabolic rates. We did so because standing rates include muscular support costs (Joseph and Nightingale, 1952;Loram et al, 2007;Weyand et al, 2009) that are also incurred during walking (Biewener et al, 2004;DeJaeger et al, 2001;Grabowski et al, 2005;Griffin et al, 2003;McCann and Adams, 2002;Weyand et al, 2009). The basal rates subtracted from both our original data and qualifying literature data were calculated from the age, gender, mass and stature of each subject using the generalized equations of Schofield et al (Schofield et al, 1985) (hereafter 'Schofield equations').…”