Adherence to Exercise Prescriptions: Effects of Prescribing Moderate Versus Higher Levels of Intensity and Frequency Michael G. Perri, Stephen D. Anton, Patricia E. Durning, Timothy U. Ketterson, Sumner J. Sydeman, Nicole E. Berlant, William F. Kanasky Jr., Robert L. Newton Jr., Marian C. Limacher, and A. Daniel Martin University of Florida Sedentary adults (N = 379) were randomly assigned in a 2  2 design to walk 30 min per day at a frequency of either 3– 4 or 5–7 days per week, at an intensity of either 45%–55% or 65%–75% of maximum heart rate reserve. Analyses of exercise accumulated over 6 months showed greater amounts completed in the higher frequency ( p = .0001) and moderate intensity ( p = .021) conditions. Analyses of percentage of prescribed exercise completed showed greater adherence in the moderate intensity ( p = .02) condition. Prescribing a higher frequency increased the accumulation of exercise without a decline in adherence, whereas prescribing a higher intensity decreased adherence and resulted in the completion of less exercise. Key words: exercise, physical activity, adherence Although the health benefits of engaging in physical activity have been well established (U.S. Department of Health and Human Services [USDHHS], 1996), 75% of American adults are inactive or insufficiently active (Centers for Disease Control and Preven- tion [CDC], 2001). The high prevalence of inactivity may be related, in part, to the public perception that a high frequency of vigorous exercise is required to achieve significant health benefits (Pate et al., 1995; Sallis & Owen, 1999). An important implication of this explanation is that the initiation and maintenance of exer- cise might be increased if the prescribed levels of physical activity were easier to achieve. The present study was designed to test this hypothesis. We examined the effects on adherence of prescribing exercise at moderate versus higher levels of intensity and frequency. Early guidelines for physical activity (e.g., American College of Sports Medicine [ACSM], 1978) focused on the attainment of cardiorespiratory fitness and emphasized the need for vigorous intensity aerobic exercise (60%–90% of maximum heart rate re- serve [HR res ]) completed 3–5 days per week, in bouts of 15– 60 min per session. By the early 1990s, reviews of epidemiological and laboratory studies (e.g., Berlin & Colditz, 1990; Blair, Kohl, Gordon, & Paffenbarger, 1992; Haskell et al., 1992) indicated that physical activity of lower intensity, duration, and frequency than that required to improve cardiorespiratory fitness could produce significant improvements in health outcomes, including a reduc- tion in the risk of coronary heart disease, hypertension, colon cancer, and diabetes mellitus, as well as a reduction in the risk of premature mortality in general. Consequently, an array of physical activity position papers recommended an accumulation of 30 min of moderate intensity physical activity on either most days of the week (Pate et al., 1995; USDHHS, 1996) or a minimum of 3 days per week (Fletcher et al., 1996; Blair et al., 1992). The reports of the CDC/ACSM (Pate et al., 1995), the Surgeon General (USDHHS, 1996), and the American Heart Association (AHA; Fletcher et al., 1996) also documented a dose–response relationship between physical activity and health outcomes and indicated that greater health benefits can be derived from engaging in physical activity of more vigorous intensity or longer duration. However, the accrual of beneficial health outcomes with higher levels of physical activity was given less emphasis because of the expectation that a prescription for moderate activity would result in greater exercise adoption and maintenance, thereby ultimately producing greater improvements in the health of the population (Fletcher et al., 1996; Pate et al., 1995; USDHHS, 1996). Data from both epidemiological and intervention studies have provided support for this perspective. For example, in a longitu- dinal community survey, Sallis et al. (1986) found that rates of exercise adoption were higher for moderate versus vigorous activ- ities and that 1-year drop-out rates were greater for vigorous activities. Similarly, in a meta-analysis of 127 intervention studies, Michael G. Perri, Stephen D. Anton, Patricia E. Durning, Timothy U. Ketterson, Sumner J. Sydeman, Nicole E. Berlant, William F. Kanasky Jr., and Robert L. Newton Jr., Department of Clinical and Health Psychology, University of Florida; Marian C. Limacher, Department of Medicine, University of Florida; A. Daniel Martin, Department of Physical Therapy, University of Florida. Sumner J. Sydeman is now at the Department of Psychology, Northern Arizona University. We are deeply grateful to our late colleague Michael L. Pollock for his inspiration and his guidance in the development of this project. We are also grateful for the assistance of Glen Duncan, Diego de Hoyos, Cheryl Giswold, Antoinette Chiara, Mark Lui, Weing Zhao, David Lowenthal, Abdel Gabr, Valerie Bonk, Kimberly McKessey, Gretchen Forbes, Robyn Wallace, Gretchen Wolff, Natalie Blevins, Joyce Corsica, Abbie Beacham, Anna Moore, Aisha Kazi, Kimberly Dempsey, and Sheila Rauch. This study was supported by National Heart, Lung, and Blood Institute Grant HL 58873 and by the National Institutes of Health for the University of Florida’s General Clinical Research Center Grant RR00082. Correspondence concerning this article should be addressed to Michael G. Perri, Department of Clinical and Health Psychology, University of Florida, P.O. Box 100165, Health Science Center, Gainesville, Florida 32610-0165. E-mail: mperri@hp.ufl.edu Health Psychology Copyright 2002 by the American Psychological Association, Inc. 2002, Vol. 21, No. 5, 452– 458 0278-6133/02/$5.00 DOI: 10.1037//0278-6133.21.5.452 452 This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.