MY husband and I were riding our bikes not long ago, and when we were about a mile from home, we did our usual thing. We call it the sprint to the finish: ride as hard and as fast as we can until we reach our driveway, racing to see who could get there first.

We pulled up, slammed on our brakes and hopped off our bikes. A neighbor was walking by and said, “How did you do that?”

“I just put on my brakes,” I told him. No, he said, he meant how could we just stop like that without cooling down?

Strange as it might seem, that had never occurred to me. But the cool-down is enshrined in training lore. It’s in physiology textbooks, personal trainers often insist on it, fitness magazines tell you that you must do it  and some exercise equipment at gyms automatically includes it. You punch in the time you want to work out on the machine and when your time is up, the machine automatically reduces the workload and continues for five minutes so you can cool down.