Prescribing exercise at varied levels of intensity and frequency: A randomized trial

Abstract

Background: Regular physical activity produces beneficial effects on health, but the exercise prescription needed to improve cardiovascular disease risk factors in free-living sedentary individuals remains unclear. Methods: Sedentary adults (N=492, 64.0% women) were randomized to 1 of 4 exercise-counseling conditions or to a physician advice comparison group. The duration (30 minutes) and type (walking) of exercise were held constant, while exercise intensity and frequency were manipulated to form 4 exercise prescriptions: moderate intensity-low frequency, moderate intensity-high frequency (HiF), hard intensity (HardI)-low frequency, and HardIHiF. Comparison group participants received physician advice and written materials regarding recommended levels of exercise for health. Outcomes included 6- and 24-month changes in cardiorespiratory fitness (maximum oxygen consumption), high-density lipoprotein cholesterol (HDL-C) level, and the total cholesterol-HDL-C ratio. Results: At 6 months, the HardI-HiF, HardI-low-frequency, and moderate-intensity-HiF conditions demonstrated significant increases in maximum oxygen consumption (P≤.01 for all), but only the HardI-HiF condition showed significant improvements in HDL-C level (P≤.03), total cholesterol-HDL-C ratio (P≤.04), and maximum oxygen consumption (P≤.01) compared with physician advice. At 24 months, the increases in maximum oxygen consumption remained significantly higher than baseline in the HardI-HiF, HardI-lowfrequency, and moderate-intensity-HiF conditions and in the HardI-HiF group compared with physician advice (P≤.01 for all), but no significant effects on HDL-C level (P=.57) or total cholesterol-HDL-C ratio (P=.64) were observed. Conclusions: Exercise counseling with a prescription for walking at either a HardI or a HiF produced significant long-term improvements in cardiorespiratory fitness. More exercise or the combination of HardI plus HiF exercise may provide additional benefits, including larger fitness changes and improved lipid profiles. ©2005 American Medical Association. All rights reserved.