Less Can Be More

November 30, 2007

Working out on a treadmill

Researchers have found that a moderate exercise program can do wonders for the heart, keeping a key blood marker linked to heart disease and diabetes low even after weeks of rest, in some cases more effectively than intense exercise.

The researchers assigned 240 middle-aged, sedentary subjects to four distinct groups. Three were exercise groups: a high amount/high intensity group, a low amount/high intensity group, and a low amount/moderate intensity group. The fourth was a control group—participants 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) when they began their programs, and then at twenty-four hours, five days, and fifteen days after they stopped doing them.

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 the benefit was sustained over time.

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," says Cris Slentz, the study's lead author and an exercise physiologist at Duke. "We wanted to measure how long those benefits linger."

He and his colleagues found that a modest, low-intensity workout—walking just thirty minutes a day, for example—dramatically lowered triglyceride levels. Triglycerides are the particles that carry fat throughout the body, and they're also an indicator of insulin resistance, a marker for diabetes. Lowering triglyceride levels lowers risk of heart disease and diabetes. "We were also amazed to see that the lower triglyceride levels stayed low even two weeks after the workouts ended," says senior author William Kraus M.D. '83, associate professor of cell biology and medicine, adding that longer, more intense workouts didn't have nearly the same impact.

While the researchers were surprised by the amount and duration of the benefits from a modest exercise program, they say they were not surprised by the "alarming" results from the control group. Over six months, those participants gained two pounds and about a half inch around the waist.

"That may not sound like much, but over a decade at that rate, that would mean an additional forty pounds and ten inches," Kraus says. "So doing a little is a whole lot better than doing nothing at all."

The study was published in the Journal of Applied Physiology.

www.jap.physiology.org