I would assume this varies greatly by individual, based on biological factors. My answer would be "enough to feel fit", where moderate levels of physical play would be considered fun rather than dreaded. For me that's about 40min/day, 4x per week, of weight training. I don't know if that's typical, but having lived on both sides of the line, the benefits of feeling fit are very easily worth that lost time. Everything else I do benefits, it's akin to getting enough sleep.
Often, there are questions you want to know the answers to. You want other people's opinions, because knowing the answer isn't worth the time you'd have to spend to find it, or you're unsure whether your answer is right.
LW seems like a good place to ask these questions because the people here are pretty rational. So, in this thread: You post a top-level comment with some question. Other people reply to your comment with their answers. You upvote answers that you agree with and questions whose answers you'd like to know.
A few (mostly obvious) guidelines:
For questions:
For answers:
This thread is primarily for getting the hivemind's opinions on things, not for debating probabilities of propositions. Debating is also okay, though, especially since it will help question-posters to make up their minds.
Don't be too squeamish about breaking the question-answer format.
This is a followup to my comment in the open thread.