Roderick Floud, et al., "The Changing Body: Health, Nutrition, and Human Development in the Western World since 1700" have a table (p. 45) that shows the relative energy requirements for men for various activities. Here are some numbers: Sleeping 1.0 Milking cows by hand 2.9 Walking at a normal pace 3.2 Carpentry 3.5 Collecting and spreading manure 6.4 and the highest rated activity.... Felling trees 7.5. These figures reflect older technology. Thank goodness for chainsaws and Fiskars! But, even with modern tools, felling trees and processing firewood is an intense activity.