As you saw intuitively, they enjoy extraordinary high energy capability to be so active, so rapid in their movements, and so strong, scampering up and down tree trunks and being on the move so much of the time. This is a good example of the array of possibilities inherent in various species where some are energetically lethargic and others hyperactive from your perspective. Humans would find it impossible to match what a squirrel does, even during a portion of its normal day, and that is owing not only to the smaller mass the squirrel contends with, but to its physical configuration with regard to energetics—to get much more energy from its metabolism and for its muscles to work in special ways to become restored more quickly, and to not have the consequences of fatigue build to the level of exhaustion requiring a prolonged period of rest for restoration of usual function. It is a difference in the way waste products are removed as well as in energy production itself. And indeed, there are many scientific clues that can be extrapolated in useful ways to enhance human performance from what can be learned about such differences.