![]() ![]() This is only true: (1) when sufficient time is given to achieve a physiological steady-state and (2) when the speed is less than that which results in accumulation of blood lactate. Thus, V ˙ O 2 reflects the quantity of ATP used when aerobic metabolism can provide all of the energy at a given running speed. O 2 is consumed when it accepts electrons at the end of the electron transport chain to form ATP via ATP synthase. Consequently, probing the specific factors that dictate the muscle energy cost during running, which include running speed, body mass, and muscle-tendon mechanical and morphological properties (tendon stiffness, fascicle length) should provide unique insight into the underlying factors that determine E run and may reveal the mechanisms behind changes in E run with training, disuse or disease.ĪTP is resynthesized from ADP and Pi using the energy released during oxidative phosphorylation. The energy cost of other active muscles, of course, also contribute to the total metabolic cost of running. This proportion increases to nearly 40% in lesser-trained male and female runners (Figure 1). Specifically, we have estimated that the energy cost of triceps surae muscles contraction during the running stride of highly-trained runners represents nearly 25% of the total metabolic cost of running. Recently, we have estimated that the active skeletal muscle energy cost represents the vast majority of the total metabolic cost of running ( Fletcher and MacIntosh, 2015). None of these reviews has approached E run from a muscle energetics standpoint. It is known that E run is likely influenced by a number of physiological and biomechanical factors and several excellent reviews have been written on the topic in the last 25 years ( Morgan et al., 1989 Morgan and Craib, 1992 Saunders et al., 2004 McCann and Higginson, 2008 Lacour and Bourdin, 2015). But how is an extraordinary E run achieved? min −1, so it is likely the runner who is going to break the sub-2 h marathon will be one with extraordinary E run.m −1 ( Fletcher et al., 2009) would only require a V ˙ O 2 m a x of 77.5 ml. ![]() A marathoner, with an excellent E run of 3.77 J E run values this low are frequently reported ( Foster and Lucia, 2007 Fletcher et al., 2009 Shaw et al., 2013), but assuming the marathon distance could be sustained at 85% V ˙ O 2 m a x, this runner would require a V ˙ O 2 m a x near 85 ml Assuming this runner has a body mass of 56 kg and their respiratory exchange ratio is 0.95, this oxygen uptake would equate to an E run of 4.39 J
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