Walking. Walk 3 miles a day. It gives you a drastically different set of benefits from running, and you can walk all day without worry of overtraining.

Running is great too. But be careful of doing it too much. Overtraining can break down your immune system and make you more susceptible to disease.

I wonder if it only works for a dedicated walking time (e.g. walk for 3 miles nonstop) or also for bursts of short walking during the day. I consistently get 3-5 miles of walking per day due to chasing kids around, taking short breaks during work, and doing chores, but rarely actually have a 30+ min sustained walk.

I walk over six kilometres (almost) every day and don't sleep well.