I had a funny thought while swimming the other day: I am traveling at less than 1 mph. On Monday evening, I got out and swam laps for the first time in awhile*. At our pool, 35 labs constitutes a mile. I managed 20 laps in the ~45 minutes worth of swimming I did. Of course, part of that time was stretching. Due to my back injury, as referenced below, I have to stretch a lot. So I stretched out after every 5 laps.
Still, I was traveling less than 1 mph. And it was still great exercise.
* I was distracted, first by running, and then by a back injury. Swimming is helping me ease back into the exercise.