Run, run, run on my running machine;
I'm a lean, mean thinking machine.
That's a cadence I composed for laughs. I run on a Star Trac elliptical machine - the "Natural Runner" model - in my basement in the early morning, either to Bubblevision news or to military cadence tapes (aka, ("Jody calls"). See http://www.startracusa.com/ or do a Google search for many dealers. It's great & I highly recommend it - mine has lasted years.
A few months ago, I read an article in The Wall Street Journal that reported clinical evidence that 30 minutes of daily aerobic exercise both stops & reverses brain shrinking as one ages. That re-motivated me to hit that running machine in the AM. I always feel better after a workout. I have more energy and can think more clearly. By the way, power walking works OK, too. I stick to the running machine since on winter days, the roads might be icy, and on early summer days the mosquitos might carry me off. :-)
So hit that workout!