The health benefits of regular physical activity have been well established. But most U.S. adults are not sufficiently active regularly, and 26 percent are not active at all, according to background information in the article. The exercise prescription needed to improve cardiovascular disease risk factors in free-living sedentary adults remains unclear.
Glen E. Duncan, Ph.D., R.C.E.P.S.M., of the University of Washington, Seattle, and colleagues conducted a randomized trial to examine the effects of exercise counseling prescriptions, varied in intensity and frequency. A total of 492 sedentary adults (177 men, 315 women) were randomized to one of four exercise counseling conditions, or to a physician advice comparison group. The duration of exercise (30 minutes) and type of exercise (walking) were the same in the four counseling groups, while exercise intensity and frequency was manipulated to form four prescriptions:
- Moderate intensity (ModI)-low frequency (LowF)
- Moderate intensity-high frequency (HiF)
- Hard intensity (HardI)-low frequency
- Hard intensity-high frequency
Intensity was defined by percentage of maximal heart rate (HR) reserve - 45-55 percent for ModI, and 65-75 percent for HardI. LowF was defined as three to four sessions per week, while HiF was five to seven sessions per week. Comparison group participants received physician advice and written materials regarding recommended levels of exercise for health. The researchers measured changes in cardiorespiratory fitness (maximum oxygen consumption), high-density lipoprotein cholesterol (HDL-C), and the ratio of total cholesterol to HDL-C.
"At six months, the HardI-HiF, HardI-low frequency, and moderate intensity-HiF conditions demonstrated significant increases in maximum oxygen consumption, but only the HardI-HiF condition showed significant improvements in HDL-C level, total cholesterol-HDL-C ratio, and maximum oxygen consumption, compared with physician advice" the authors write.
"At 24 months, the increases in maximum oxygen consumption remained significantly higher than baseline in the HardI-HiF, HardI-low frequency, and moderate intensity-HiF conditions and in the HardI-HiF group compared with physician advice, but no significant effects on HDL-C or total cholesterol-HDL-C ratio were observed," they continue.
"The findings demonstrate that significant improvements in cardiorespiratory fitness can be achieved and maintained over 24 months via exercise counseling with a prescription for walking 30 minutes per day, either at a ModI five to seven days per week, or at a HardI three to four days per week," the authors conclude. "Additional benefits, including larger changes in fitness and increases in HDL-C level, may be achieved by prescribing either more exercise or the combination of HardI plus HiF exercise."
(Arch Intern Med. 2005; 165: 2362-2369. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: This study was supported by a Polar Research Award to Dr. Duncan from the American College of Sports Medicine Foundation, Indianapolis, Ind., and Polar Research; by a grant from the National Institutes of Health, Bethesda, Md., to co-author Michael G. Perri, Ph.D.; and by a grant from the General Clinical Research Center, National Institutes of Health. Dr. Duncan received an American Heart Association/Florida-Puerto Rico Affiliate Postdoctoral Fellowship.
Editorial: How Much and What Type of Physical Activity is Enough?
In an accompanying editorial, Steven N. Blair, P.E.D., and Michael J. LaMonte, Ph.D., of the Cooper Institute, Dallas, write that the findings of Duncan and colleagues carry important public health and clinical implications.
"In summary, Duncan et al have demonstrated that various combinations of exercise frequency and intensity, yielding a modest total physical activity dose, can be effective in increasing aerobic power," they write. "Individuals who choose to exercise at a higher intensity (65-75 percent of maximal HR reserve) can make significant improvements in their fitness by walking for 30 minutes three or four days per week. Likewise, persons who prefer a lower intensity of 45 to 55 percent can obtain similar benefits by walking for 30 minutes five to seven days per week."
"The findings reported by Duncan et al are further evidence of the opportunity that practitioners have in counseling their patients on a health behavior that has critical importance for primary and secondary disease prevention," they conclude.
(Arch Intern Med. 2005; 165: 2324-2325. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: The current work of Drs. Blair and LaMonte on topics relevant to this editorial is supported in part by grants from the National Institutes of Health, Bethesda, Md.; equipment grants from Life Fitness, Schiller Park, Ill.; and support from Nancy Ann and Ray L. Hunt through the Communities Foundation of Texas, Dallas.
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