UF researchers: Few adults are reaching recommended intensity during physical activity

August 22, 2001

GAINESVILLE, Fla. --- Many physically unfit adults think they exercise more vigorously than they do, a misperception that may hamper their efforts to prevent heart disease, University of Florida researchers report.

The researchers agree that any physical activity is better than none, but those who exercise at the moderate and high intensity levels see the greatest benefits. Activity levels of 66 sedentary adult men and women were evaluated for one week to assess the frequency, intensity and duration of their physical activities.

Researchers found that study participants accurately reported the amount of daily exercise, but most did not accurately report level of intensity. The researchers hope the findings will lead to a re-evaluation and clarification of traditional exercise protocols that recommend intensity levels.

"There is a clear relationship between the amount of physical activity a person engages in and the risk for heart disease," said Glen E. Duncan, principal investigator of the study published in the July issue of Preventive Medicine. "Most of the sedentary adult population cannot achieve the recommended intensity level of activity." Duncan is a postdoctoral associate in UF's College of Medicine.

Approximately 960,000 Americans die from cardiovascular disease every year, with 250,000 of those deaths attributed to a lack of regular physical activity.

Surveys show that a quarter of Americans do not participate in any physical activity and of those who do, only 46 percent do it regularly and intensely enough to protect their hearts.

The American Heart Association provides specific guidelines for exercise aimed at lowering the risk of heart disease and heart attack, high blood pressure, high cholesterol, obesity and diabetes. Physical benefits also include strengthening of muscles and bones, boosting energy and improving weight control.

The research was conducted as part of UF's ongoing "walking project," sponsored by the National Heart, Lung and Blood Institute and led by clinical and health psychologist Michael G. Perri, a professor in UF's College of Health Professions. Researchers hope to answer the questions of how often and how hard people should exercise to receive the greatest cardiovascular benefits. The four-year study began in fall 1998.

"Seventy-five percent of all Americans are either sedentary or getting less physical activity than seen as appropriate for good health," said Perri, co-principal investigator of the study.

The study participants, volunteers from Gainesville, Fla., and surrounding communities, were adults who had been exercising moderately for less than an hour each week. To make sure the volunteers were able to engage safely in vigorous exercise activities, physical examinations and stress tests were conducted before admittance to the study. Participants were interviewed to recall the amount and level of their daily activity for the previous week. That information was compared with measurements recorded by heart rate monitors and activity logs completed by the participants.

In their activity logs, 47 percent of the volunteers wrote that they participated in moderate activity for at least 10 minutes, but the heart rate monitors showed that only 15 percent reached moderate intensity. While 11 percent reported exercising at the hard intensity level, heart rate monitors revealed that fewer than 2 percent reached that level.

"The results reveal that we must use caution in interpreting what sedentary adults tell us about their exercise habits, since they commonly overestimate the intensity of moderate activity," said Paul M. Ribisl, chairman of the department of health and exercise science at Wake Forest University.

"This could possibly give us misleading information about health benefits from such activity when using self-report data. Health-care professionals need simple methods to track these behaviors if they are to determine effective strategies."

Research suggests that in order to better protect themselves from heart disease, people should maintain a moderate to hard intensity level of activity that increases their metabolism to six times their energy consumption during rest. The exercise should be done three to four times a week for 30 minutes to one hour. Moderate intensity is equivalent to a brisk walk. Hard intensity is defined as a level equivalent to jogging.

"The problem that we found is, for both moderate and hard levels, sedentary people are not accurate in judging how intensely they are exercising," Perri said. In light of these findings, Duncan suggests adults need better guidance when defining their level of activity.

University of Florida

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