a. How much metabolic energy is required for a \(68 \mathrm{~kg}\) runner to run at a speed of \(15 \mathrm{~km} / \mathrm{h}\) for \(20 \mathrm{~min}\) ?

b. How much metabolic energy is required for this runner to walk at a speed of \(5.0 \mathrm{~km} / \mathrm{h}\) for \(60 \mathrm{~min}\) ? Compare your result to your answer to part a.

c. Compare your results of parts \(\mathrm{a}\) and \(\mathrm{b}\) to the result of Example 11.4. Of these three modes of human motion, which is the most efficient?

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EXAMPLE 11.4 Energy usage for a cyclist A cyclist pedals for 20 min at a speed of 15 km/h. How much metabolic energy is required? How much energy is used for forward propulsion? PREPARE Table 11.4 gives a value of 480 W for the metabolic power used in cycling at 15 km/h. 480 W is the power used by the body; the power going into forward propulsion is much less than this. The cyclist uses energy at this rate for 20 min, or 1200 s.