The application of stress, the recovery from that stress, and the subsequent adaptation that results from the process is the central organizing principle of everything that has to do with physical improvement. From physical and occupational therapy to preparation for the Olympic Games, the stress/recovery/adaptation cycle is not just a good idea, it’s the law.
It is May 15, and you decide that this year you are going to get a suntan — a glorious, beautiful, tropical suntan. So you decide to catch some rays outside at lunchtime. You lie on your back for 15 minutes and flip over to lie on your belly for 15 minutes. Then you come in and eat lunch, and go back to work. That night, your skin is a little pink, so the next day you just eat lunch, but the following day you’re back outside for your 15 minutes-per-side sunbath.
You are faithful to your schedule, spending 30 minutes outside every day that week. At the end of the week, you have turned a more pleasant shade of brown, and — heartened by your results — resolve to maintain your schedule for the rest of the month.
The critical question: what color is your skin at the end of the month?
If you ask a hundred people this question, ninety five will tell you that it will be really, really dark. But in fact it will be exactly the same color it was at the end of the first week. Why would it be any darker?
“Stress” is that which causes a perturbation of the steady state of a system — in this case, your physiology. If the stress is mild, it causes no response. It doesn’t disrupt the situation enough to be noticed. If the stress is too great, it can kill you. This is what happens when you fall off a building or get mauled by a bear.