Although pro sportspeople can have huge energy outputs in single matches, those that go to extremes (like marathons on consecutive days for weeks, or riding a G

Although pro sportspeople can have huge energy outputs in single matches, those that go to extremes (like marathons on consecutive days for weeks, or riding a Grand Tour race, or being pregnant -- they looked at a wide range of things) won't exceed 2.5 times their normal "rest" energy output per day, after a few weeks. Even if their pace doesn't go down much, so they become more efficient after those weeks. There is also research from gorging for weight gain that concludes that the body can't take in more than 2.5x the daily "rest" energy use in calories, so the two seem linked.