When Exercise Stops, How Long Do Benefits Last?

Scientists examining the relationship between the intensity and length of a workout and the duration of its benefits have made a surprising discovery: More isn't necessarily better, and none may be worse than we ever imagined.

"On the surface, it seems to make sense that the harder we exercise, the better off we'll be, and by some measures that's true," says lead author Cris Slentz, Ph.D, an exercise physiologist at Duke University Medical Center. "But our studies show that a modest amount of moderately intense exercise is the best way to significantly lower the level of a key blood marker linked to higher risk of heart disease and diabetes. More intense exercise doesn't seem to do that."

What may be even more remarkable, he says, is that some of the benefits derived from a modest exercise regimen appear to last much longer than those gained from a more rigorous program.

The study was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health and is slated for the August issue of the Journal of Applied Physiology.

Slentz, along with senior author William, Kraus, M.D., a Duke cardiologist, studied 240 middle-aged, sedentary people randomized into one of four groups. Three of them were exercise groups: a high amount/high intensity group, a low amount/high intensity group and a low amount/moderate intensity group. Members of the fourth group were controls, meaning they didn't do any exercise at all. Workouts included time on a treadmill, an elliptical trainer and a stationary bicycle. Participants went through a two-to-three month ramp-up period, then stayed on their programs for six months. Scientists measured the participants' blood levels of proteins that carry cholesterol and fat ( HDL, LDL and triglycerides) at the beginning of their programs, and then at 24 hours, five days, and 15 days after they ended. (The trial is called STRRIDE: Studies of a Targeted Risk Reduction Intervention Through Defined Exercise.)

The researchers were especially interested in what happened after the participants stopped their workouts. "There are lots of studies that demonstrate the benefits of exercise, but we also know that in real life, people don't always adhere to their programs, so we wanted to measure how long those benefits linger," says Slentz. Such studies may help scientists understand why certain changes with exercise occur in the first place, and that may ultimately help them design more tailored programs for people who want to improve their health.

The researchers found that for the most part, no amount of exercise significantly changed LDL levels. HDL levels, however, tended to improve with the length and intensity of the workout, and that the benefit was sustained over time.

But perhaps the most interesting finding was that a modest, low-intensity workout