Recent studies have found that interval training (alternating between high-and moderate-intensity bursts of activity) can double and possibly even triple the heart-protecting benefits you'd get from moderate cardio sessions--even when you exercise for less time…The best part: "You gauge the intensity based on your own fitness level," says Sharonne N. Hayes, MD, a cardiologist and founder of the Women's Heart Clinic at the Mayo Clinic in Rochester, MN. That might be a brisk walk for you, while it could be a fast jog for someone else.
Prevention, by Ginny Graves, 1/15/2012