“For a long time, the theory was that cooling down by continuing to exercise at a lower intensity would help the legs flush out lactate” and avoid soreness the next day, said Ross Tucker, a South African physiologist and a founder of the website The Science of Sport. “That’s still dogma among many coaches and athletes.”
But it is a myth. “We now know that lactate isn’t responsible for muscle damage or soreness,” Dr. Tucker said, and cooling down does not rid muscles of it anyway.
The available scientific evidence shows, in fact, little benefit from cooling down as most of us do it, with a prolonged, slow easing of physical effort. In a representative 2007 study, healthy adults briskly walked for 30 minutes backward on a treadmill set at an incline to simulate going downhill, an activity known to induce sore muscles.
Some of the group warmed up first with a gentle, forward-facing 10-minute walk. Others did the same afterward, as a cool-down. A few did neither. Two days later, the walkers who had warmed up reported less muscle soreness than the others. But those who had cooled down were just as sore as those in the control group.
Which is not to say that you should abruptly end a workout. During lengthy, strenuous exercise, blood vessels in your legs expand, and blood can pool there if you shift suddenly from high to zero exertion, resulting in dizziness or fainting. A few minutes of jogging, walking or other light exertion will normalize blood flow, Dr. Tucker said.
Meanwhile, there is no evidence that longer cool-downs are harmful, Dr. Tucker pointed out, so if you enjoy cooling down, continue. You have little to lose, except time.