Try it: The next day, once inflammation has subsided.
How it works: “A walk or a swim does wonders,” says Amy Manson, a trainer in Boulder, Colorado. “By increasing circulation, you speed the healing process and flush out the lactic acid,” which is what makes you feel stiff. “Pain-masking endorphins are also released,” she says.
Bear in mind: Take it slow. The point is to eliminate lactic acid, not produce more. “Walk or use a stationary bike,” suggests Harley Pasternak, a trainer in Los Angeles and the author of The 5 Factor World Diet ($5, amazon.com).