Exercise counseling with a prescription for walking at either hard intensity or high frequency produces improvements in cardiorespiratory fitness.

The study is published in the Archives of Internal Medicine.

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.
The exercise prescription needed to improve cardiovascular disease risk factors in free-living sedentary adults remains unclear.

Glen E. Duncan, 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 moderate intensity, and 65-75 percent for hard intensity. Low intensity was defined as three to four sessions per week, while high frequency 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 hard intensity- high frequency, hard intensity-low frequency, and moderate intensity- high frequency conditions demonstrated significant increases in maximum oxygen consumption, but only the hard intensity - high frequency 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 hard intensity- high frequency, hard intensity - low frequency, and moderate intensity- high frequency conditions and in the hard intensity – high frequency 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 moderate intensity five to seven days per week, or at a hard intensity 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 hard intensity plus high frequency exercise."

In an accompanying editorial, Steven N. Blair, and Michael J. LaMonte, of the Cooper Institute, Dallas, write that the findings of Duncan and colleagues carry important public health and clinical implications.

" 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.

Source: American Medical Association, 2005


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