“…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.…”