Walk this way: UF research provides insight into heart healthy exercise regimen

November 14, 2005

GAINESVILLE, Fla. — Thirty minutes of brisk walking a day is a step in the right direction toward improved heart health, according to a University of Florida study published in today’s (Nov. 14) Archives of Internal Medicine.

UF researchers found that study participants who were prescribed an exercise regimen of walking for 30 minutes five or more days a week at either a moderate or hard intensity, or at a hard intensity three to four days a week, showed significant long-term improvements in cardiorespiratory fitness. Fast-paced, frequent walking offered the largest fitness benefits and also led to modest, short-term improvements in cholesterol levels.

A half hour of moderate-intensity walking most days of the week has been associated with significant health benefits and is in line with recommendations from the American Heart Association, the Centers for Disease Control and Prevention, and the U.S. Surgeon General. But instead of evaluating weight loss, the UF study focused specifically on exercise’s effects on heart health and addressed the wide variability in people’s adherence to exercise regimens, which health providers must take into account when counseling patients.

“National guidelines for exercise are based largely on studies conducted in laboratory settings with close supervision of how much exercise is completed by the study participants,” said principal investigator Michael Perri, associate dean and a professor of clinical and health psychology in UF’s College of Public Health and Health Professions. “In our research, we were very interested in learning about the ways people respond to different exercise prescriptions when they are asked to complete the exercise on their own, in their home or work environments.”

Exercise at either high frequency or hard intensity seems to be the key, the researchers discovered.

“When exercising on their own, people generally complete only about 60 percent of the amount prescribed,” Perri said. “As a result, an exercise prescription for moderate-intensity walking on three to four days a week may not generate a large enough amount of exercise to produce a change in fitness.”

In the two-year study, UF researchers evaluated 500 sedentary men and women ages 30 to 69 who were randomly assigned to one of four exercise groups or to a comparison group that only received group counseling by a physician. The duration and type of exercise prescribed were the same for each of the exercise groups — 30 minutes of walking a day — but the intensity and frequency varied.

Measurements of cardiorespiratory fitness, high-density lipoprotein, or HDL, cholesterol — the “good” form — and the ratio of total cholesterol to HDL were taken at baseline, at six months and at two years.

At the two-year follow-up, 21 percent of the participants who walked five or more days a week or three to four days a week at a fast pace had a 10 percent or greater improvement in cardiorespiratory fitness, compared with 14 percent of the participants in the low-frequency exercise or comparison group. While the changes may appear modest, previous studies have shown that a 10 percent increase in cardiorespiratory fitness may result in a 15 percent reduction in mortality.

At six months, participants in high-frequency or high-intensity exercise groups showed a significant increase in cardiorespiratory fitness, but only those who walked at a fast pace five to seven days a week had significant improvements in HDL or the ratio of total cholesterol to HDL.

Cardiorespiratory fitness levels remained high in these groups when measured again at two years, but improvements in cholesterol profiles were not sustained, perhaps due to diminished adherence to the regimen, Perri said.

The difference between the amount of exercise prescribed and the amount likely to be performed should be taken into account when health providers make recommendations to their patients, the researchers say.

“I was most surprised by how much variability there was in how closely the participants followed their exercise prescriptions,” said the paper’s lead author Glen Duncan, an assistant professor of epidemiology in the nutritional sciences program at the University of Washington.

Further research should involve developing approaches to encourage people to exercise, Duncan said. Most American adults aren’t sufficiently active on a regular basis, and 26 percent are not active at all.

“I believe that we really need to get a handle on how we can engage adults and children in physical activity so that they are active on a regular basis,” Duncan said. “There are many reasons why people are not active. This is unfortunate because we know that exercise works very well in terms of improving health, but it works only insomuch as people actually do the exercise.”

The UF study provides valuable information that health practitioners can use when counseling their patients on exercise plans, write Steven Blair and Michael LaMonte of the Cooper Institute, in an editorial accompanying the journal article.

“This study makes important contributions to our understanding of how much exercise is necessary to produce important physiological adaptations,” Blair said. “The bottom line is that 30 minutes of walking on five to seven days a week provides substantial health benefits.”