Some 45 million Americans belong to a gym or exercise on their own, hoping to improve their physical fitness and their health. Gretchen Reynolds, writer of the New York Times Phys Ed column and author of The First 20 Minutes, answers questions and debunks myths about exercise. She explains the latest research on the mental and physical benefits of exercise and tells how much and what kind of exercise is needed to stay fit, improve health, or lose weight.

If you have a question about exercise, leave it as a comment! Or call during the show at 212-433-9692.