health span versus disease span—the amount of time you are able to avoid declining health and live a fully productive, self-sufficient life. There’s a parallel concept called productivity span that can apply not just to the arc of your life but also to the arc of a single day: There are times of day when you are at your best and other times when you are not. I mentioned this earlier in the discussion of chronotypes and the fact that older adults tend to perform better in the morning (whenever that subjective morning is—the first six hours of being awake).
