Artigo - Prescribing Exercise at Varied Levels of Intensity and Frequency

ORIGINAL INVESTIGATION Prescribing Exercise at Varied Levels of Intensity and Frequency A Randomized Trial Glen E. Duncan, PhD, RCEPSM; Stephen D. Anton, PhD; Sumner J. Sydeman, PhD; Robert L. Newton, Jr, PhD; Joyce A. Corsica, PhD; Patricia E. Durning, PhD; Timothy U. Ketterson, PhD; A. Daniel Martin, PhD, PT; Marian C. Limacher, MD; Michael G. Perri, PhD Background : Regular physical activity produces ben- eficial 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 con- stant, while exercise intensity and frequency were ma- nipulated to form 4 exercise prescriptions: moderate in- tensity\u2013low frequency, moderate intensity\u2013high frequency (HiF), hard intensity (HardI)\u2013low frequency, and HardI- HiF. Comparison group participants received physician advice and written materials regarding recommended lev- els of exercise for health. Outcomes included 6- and 24- month changes in cardiorespiratory fitness (maximum oxy- gen consumption), high-density lipoprotein cholesterol (HDL-C) level, and the total cholesterol\u2013HDL-C ratio. Results : At 6 months, the HardI-HiF, HardI\u2013low-fre- quency, and moderate-intensity\u2013HiF conditions dem- onstrated significant increases in maximum oxygen consumption ( P \u2b0d .01 for all), but only the HardI-HiF condition showed significant improvements in HDL-C level ( P \u2b0d .03), total cholesterol\u2013HDL-C ratio ( P \u2b0d .04), and maximum oxygen consumption ( P \u2b0d .01) compared with physician advice. At 24 months, the increases in maximum oxygen consumption remained significantly higher than baseline in the HardI-HiF, HardI\u2013low- frequency, and moderate-intensity\u2013HiF conditions and in the HardI-HiF group compared with physician advice ( P \u2b0d .01 for all), but no significant effects on HDL-C level ( P = .57) or total cholesterol\u2013HDL-C ratio ( P = .64) were observed. Conclusions : Exercise counseling with a prescription for walking at either a HardI or a HiF produced signifi- cant long-term improvements in cardiorespiratory fit- ness. More exercise or the combination of HardI plus HiF exercise may provide additional benefits, including larger fitness changes and improved lipid profiles. Arch Intern Med. 2005;165:2362-2369 T HE HEALTH BENEFITS OF EN - gaging in regular physical activity have been well es- tablished. 1-5 However, most US adults are not suffi- ciently active regularly, and 26% are not ac- tive at all. 6 Guidelines recommended by the American Heart Association, 7 the Centers for Disease Control and Prevention/ American College of Sports Medicine, 8 and the US Surgeon General 9 suggest that the accumulation of 30 minutes of moderate- intensity (ModI) physical activity on most days of the week will produce significant health benefits. The reports supporting these guidelines also describe a dose- response relationship between physical ac- tivity and health outcomes. Moderate- intensity (45%-60% of heart rate reserve [HRres]) activities completed on as few as 3 d/wk may produce observable changes in disease risk factors, and greater benefits gen- erally accrue from engaging in exercise of greater intensity or volume. 7-9 Indeed, re- cent analyses 10,11 of the dose-response is- sue affirm an inverse and generally linear relationship between physical activity and cardiovascular disease (CVD)\u2013related mor- bidity and mortality. However, because of the large variability in adherence that oc- curs when individuals are advised to per- form unsupervised exercise in their natu- ral environments, the exercise prescription required to produce beneficial changes in CVD risk factors among free-living seden- tary adults requires further research. 12 See also pages 2324 and 2355 Author Affiliations are listed at the end of this article. (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2362 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from The present study examines the effects of 4 exercise- counseling prescriptions, varied in intensity (\u201cmoder- ate\u201d [45%-55% HRres] vs \u201chard\u201d [65%-75% HRres]) and frequency (\u201clow\u201d [3-4 d/wk] vs \u201chigh\u201d [5-7 d/wk]), on selected CVD risk factors compared with a control group that received exercise advice from a physician without programmatic counseling. Our primary objective was to test the hypothesis that exercise counseling with a pre- scription for hard-intensity (HardI) and/or high- frequency (HiF) exercise would produce significantly greater improvements in maximum oxygen consump- tion (V \u02d9 O 2 max), high-density lipoprotein cholesterol (HDL-C) level, and total cholesterol (TC)\u2013HDL-C ra- tio, when compared with the physician advice (PA) group. METHODS STUDY POPULATION This single-center randomized trial, approved by the Institu- tional Review Board of the University of Florida, was con- ducted from May 1, 1998, to April 30, 2003. Participants were 492 healthy but sedentary women (n = 315) and men (n = 177), recruited primarily through advertisements. Eligibility require- ments included age (30-69 years), sedentary lifestyle ( \u2b0d 1 h/wk of ModI or greater leisure time physical activity during the prior year), body mass index (calculated as weight in kilograms di- vided by the square of height in meters) (19-45), and normal resting blood pressure ( \u2b0d 140/90 mm Hg, with or without medi- cation). Following telephone screening, potentially eligible per- sons attended an informational meeting during which in- formed consent was obtained. Potential participants completed a medical history, exercise testing, and laboratory measures of endocrine, hematological, and metabolic function. Individu- als with abnormal findings were excluded from participation. Five cohorts of approximately 100 participants were recruited and randomized at 3- to 4-month intervals. STUDY MEASURES The primary outcome measures were V \u02d9 O 2 max, HDL-C level, and TC/HDL-C ratio. These variables were selected because increases in cardiorespiratory fitness and improved blood lipid profile, particularly increases in HDL-C level, likely contribute to the protective effects of physical activity against CVDs. 13,14 Study measurements were taken at 3 assessment periods (base- line, 6 months, and 24 months). Participants performed a graded treadmill exercise test to volitional fatigue, according to the Bruce protocol. 15 Participants were required to meet 2 of 3 standard criteria for having achieved V \u02d9 O 2 max (ie, HR, age- predicted maximum HR or greater; respiratory exchange ratio \u2c56 1.10; or rating of perceived exertion \u2c56 19). Pulmonary gas exchange variables were measured continuously using a meta- bolic cart (TrueMax 2400; ParvoMedics, Inc, Sandy, Utah). Pulmonary ventilation (calculated in liters per minute) was measured by a pneumotachygraph that was calibrated daily and fractions of oxygen and carbon dioxide via analyzers that were calibrated with gases of known concentration before each test. The HR was measured by a continuous 12-lead electrocar- diogram. The maximal HR was taken as the highest value recorded during or immediately following exercise, and V \u02d9 O 2 max was defined as the average of two 30-second values measured during the last minute of exercise. Resting HR was taken as the average of 3 seated measurements, performed and averaged over 2 different days. The HRres was calculated as the difference between maximal HR and resting HR. At each assessment period, a fasting blood sample was collected on 2 separate days, and average values were used in data analyses. Lipid and lipoprotein profiles were analyzed at the University of Florida\u2019s Clinical Chemistry Laboratory, using methods rec- ommended by the National Cholesterol Education Program. The coefficients of variation for TC in this laboratory, which is accredited by the College of American Pathologists, are less than 3%. More specifically, at a control level of 133 mg/dL (3.44 mmol/L), the coefficient of variation was 1.04%, and at a control level of 242 mg/dL (6.26 mmol/L), the coefficient of variation was 1.12%. EXPERIMENTAL DESIGN Following stratification by age and sex, participants were ran- domly assigned to the PA comparison group or to 1 of the 4 exercise-counseling conditions: ModI\u2013low frequency (LowF), ModI-HiF, hard intensity (HardI)\u2013LowF, or HardI-HiF. The computerized randomization was performed using SAS statis- tical software (PROC PLAN). 16 EXERCISE COUNSELING Exercise Prescriptions Participants in the counseling conditions were provided indi- vidualized training HR zones (THRZs) using specific percent- ages of HRres 15 derived from their baseline graded treadmill exercise test performances. The THRZs corresponded to 45% to 55% HRres in the ModI conditions and 65% to 75% HRres in the HardI conditions. Participants in the LowF conditions were asked to walk 3 to 4 d/wk, while those in the HiF condi- tions were asked to walk 5 to 7 d/wk. Each participant was provided a HR monitor (Polar Beat; Polar, Inc, Port Washing- ton, NY), and was instructed to wear the monitor during each exercise session and to record the most frequently observed HR in a log. Participants were instructed to adjust their pace of walking to intensity levels consistent with their prescribed THRZs for 30 min/d for the prescribed number of days per week. The walking could occur at home, at a work site, or at other walking-friendly sites in sessions of 10 minutes or longer. Counseling Sessions Participants followed a standard exercise intervention pro- gram based on a modified version of the protocol used by Dunn et al. 17 The intervention was delivered in 2 phases: an exercise adoption phase that included 11 group sessions over 6 months and an exercise maintenance phase that included 6 quarterly group sessions over the remaining 18 months. The interven- tion included goal setting, self-monitoring, problem solving, cognitive reframing (ie, substituting positive self-statements for negative ones), and didactic presentations on topics such as proper techniques for warm-ups and cooldowns and the avoid- ance of exercise-related injuries. Training Logs Participants were instructed in the use of daily training logs for self-monitoring of the duration, intensity, and frequency of exercise. To corroborate self-reported HR values recorded during exercise sessions, each participant was asked to com- plete a 30-minute walk on 3 separate occasions while wearing a recordable HR monitor. The stored data were later down- (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2363 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from loaded, and the percentage of time that the participant\u2019s exer- cise HR was within the prescribed THRZ was calculated. In the ModI conditions, 88% of the exercise sessions showed mean HRs within the prescribed THRZ, 2% were below pre- scription, and 10% exceeded the prescription. In the HardI conditions, 71% of the sessions had mean HRs within the pre- scribed THRZ, 6% exceeded the prescribed intensity, and 23% were below prescription, as previously reported. 18 PHYSICIAN ADVICE Participants assigned to the PA condition received one 90- minute group session of advice from a physician member of the investigative team (M.C.L.) who described the benefits and risks of physical activity, presented detailed recommenda- tions for exercise, and distributed copies of an American Heart Association booklet. 19 The participants were instructed on how to measure HR, and they were advised to accumulate 30 min- utes of ModI exercise on 5 d/wk or more. The group did not receive HR monitors or activity logs. The participants met as a group quarterly, with the same physician (M.C.L.) who con- ducted an informal 5-minute question-and-answer session re- garding exercise and encouraged adherence to the American Heart Association recommendations. A guest speaker then pre- sented a 45-minute lecture on a health topic unrelated to CVD or exercise. STATISTICAL ANALYSES The data were evaluated with analysis of variance procedures using SAS statistical software (PROC GLM). 16 The effects of con- ditions during the exercise adoption phase were examined us- ing an analysis that included only those participants with base- line and 6-month data. The long-term effects of the treatment conditions were examined using an intent-to-treat procedure, substituting baseline values for missing 24-month data. Be- fore data collection, planned contrasts were identified to test the hypotheses that counseling participants with a prescrip- tion to exercise at a HardI and/or HiF would produce signifi- cantly greater improvements in V \u02d9 O 2 max, HDL-C level, and TC/ HDL-C ratio when compared with the PA condition. These tests (2-tailed) were executed using the contrasts option within the GLM procedure in SAS statistical software. 16 The independent variable in all analyses was randomization assignment. Data from all participants were analyzed according to the condition to which they were assigned, regardless of intervention session attendance or exercise adherence. Adjustments for age, sex, and baseline body mass index in these analyses were nonsignifi- cant, producing results similar to the unadjusted analyses. Data are given as mean ± SD unless otherwise indicated. RESULTS BASELINE CHARACTERISTICS A total of 2165 people made telephone inquiries about the study, and 877 underwent screening for eligibility. The criteria for participation were met by 553 individu- als, and 492 accepted randomization into the study. The sample included 315 women and 177 men. The ethnic/ racial makeup was 76.4% white (not of Hispanic ori- gin), 15.9% African American (not of Hispanic origin), 4.1% Hispanic, 2.6% Asian American or Pacific Is- lander, and 1.0% American Indian or Alaskan native. The age of the sample was 48.4 ± 8.7 years, and the years of education were 15.1 ± 3.3. Of the participants, 75.0% were in the lowest quartile of fitness based on age- and sex- adjusted norms. 20 The baseline characteristics ( Table 1 ) were similar for all conditions ( P \u2b0e .05 for all); however, among women, the between-group difference in body mass index approached significance ( P \u2b0d .06). ATTENDANCE AND ADHERENCE The overall rates of attendance (71.4% ± 21.2%) at coun- seling sessions were equivalent across conditions. At 6 months, 411 participants (83.5% of those randomized) returned for repeated measurement, and at 24 months, 342 participants (69.5%) returned for final assessments. The rates of return were equivalent across conditions. Data from the daily training logs were used to examine adher- ence to the exercise prescriptions during the exercise adop- tion phase of the study. As expected, the HiF prescrip- tions resulted in more exercise completed over 6 months than the LowF prescriptions (95 ± 65 min/wk for ModI- HiF and 88 ± 55 min/wk for HardI-HiF vs 63 ± 33 min/wk for ModI-LowF and 51 ± 35 min/wk for HardI-LowF; P \u2b0d .001 for each). When viewed as percentages of pre- scribed exercise completed, similar levels of adherence were observed for exercise prescribed at a low or HiF (62.7% vs 60.9%), but the ModI prescriptions produced greater adherence than did the HardI prescriptions (65.8% vs 57.8%; P \u2b0d .03). Most exercise sessions (83.9%) were com- pleted in sessions that were 20 minutes or longer, and there were no significant between-group differences in the use of shorter sessions ( P \u2b0e .10 for all). VOLUME OF EXERCISE The volume (metabolic equivalent hours per week) of exercise completed by participants in the exercise- counseling conditions was calculated as follows: [mean weekly hours of exercise \u2afb assigned intensity (using the lower end of the target HRres zone, ie, 45% for ModI and 65% for HardI) \u2afb V \u02d9 O 2 max (expressed as milliliters per ki- logram per minute)]/3.5. The metabolic equivalent hours per week of exercise by condition were 6.77 ± 1.76 for HardI-HiF, 5.02 ± 1.09 for ModI-HiF, 4.00 ± 0.92 for HardI- LowF, and 3.64 ± 0.81 for ModI-LowF. All 4 conditions differed significantly from each other with respect to vol- ume of exercise completed ( P \u2b0d .05 for all). CARDIORESPIRATORY FITNESS Table 2 contains the 6-month changes in fitness ex- pressed in absolute values (liters per minute). The analy- sis of variance conducted on the percentage change from baseline ( Figure ) indicated a significant treatment effect ( P \u2b0d .001). Significant increases in V \u02d9 O 2 max were ob- served in the HardI-HiF, HardI-LowF, and ModI-HiF con- ditions ( P \u2b0d .01 for each). In addition, the HardI-HiF con- dition produced a significantly greater change in V \u02d9 O 2 max compared with the ModI-LowF and PA groups ( P \u2b0d .01). Planned contrasts showed significantly greater improve- ments for the HardI and HiF prescriptions vs PA ( P \u2b0d .01 for each) and for the combination of HardI plus HiF vs PA ( P \u2b0d .001). (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2364 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from The analysis of variance conducted on the percentage change from baseline to 24 months (Figure) also showed a significant treatment effect ( P \u2b0d .01). Significant improve- ments from baseline were observed in the HardI-HiF, HardI- LowF, and ModI-HiF conditions ( P \u2b0d .01 for each), and the HardI-HiF condition demonstrated a significantly greater increase in V \u02d9 O 2 max compared with the ModI-LowF and PA groups ( P \u2b0d .01 for each). Planned contrasts showed significant improvements in fitness over 24 months for the HardI and HiF prescriptions vs PA ( P \u2b0d .02 for each) and for the combination of HardI plus HiF vs PA ( P \u2b0d .01). The fitness results were similar when the percentage changes in V \u02d9 O 2 max were expressed in weight-relative terms (milliliters per minute per kilogram). Table 3 contains the 24-month changes in fitness expressed in absolute values. LIPIDS, LIPOPROTEINS, AND OTHER MEASURES Analyses of variance conducted on percentage change from baseline to 6 months indicated a significant treat- ment effect on TC/HDL-C ratio ( P = .05) but no signifi- cant effects of treatment on TC ( P = .51), LDL-C ( P = .68), or HDL-C ( P = .13) (Table 2). Planned con- trasts showed that only the HardI-HiF condition improved significantly compared with the PA group for percentage change from baseline to 6 months in HDL-C level (3.88 ± 1.20 mg/dL [0.10 ± 0.03 mmol/L] vs 0.99 ± 1.07 mg/dL [0.03 ± 0.03 mmol/L], respectively; P \u2b0d .03) and TC/HDL-C ratio (\u22123.32 ± 0.92 vs 0.78 ± 1.15, respectively; P \u2b0d .04). There were no signifi- cant treatment effects on percentage change from base- line to 24 months for any of the lipid or lipoprotein variables ( P \u2b0e .20 for all), and all planned comparisons failed to show significant effects ( P \u2b0e .20 for all) (Table 3). In addition, the exercise conditions did not show significant changes in body weight ( P = .78), blood pressure ( P = .26), diastolic blood pressure ( P =.21), or blood glucose levels ( P = .44). COMMENT In this study, exercise counseling with a prescription for walking (30 min/d) at either a ModI 5 to 7 d/wk or a HardI 3 to 4 d/wk produced significant improvements in car- diorespiratory fitness that were observed at 6 months and maintained over 24 months. Counseling participants to exercise at a HardI and a HiF led to the largest overall increase in V \u02d9 O 2 max (7.9% at 6 months and 5.1% at 24 months). Moreover, compared with the PA group, the Table 1. Select Baseline Characteristics of Men and Women in the Study Sample * Characteristic Condition HardI-HiF ModI-HiF HardI-LowF ModI-LowF P A Men No. of subjects 38 38 30 37 34 Age, y 51.5 ± 9.8 49.0 ± 8.2 52.3 ± 10.1 49.1 ± 8.0 51.1 ± 10.7 BMI 28.9 ± 5.2 28.6 ± 4.3 28.2 ± 4.1 28.5 ± 4.1 27.6 ± 4.6 V \u02d9 O 2 max, mL/kg/min 29.6 ± 6.5 29.2 ± 5.0 29.6 ± 5.4 29.7 ± 4.3 30.0 ± 5.5 TC, mg/dL 188.8 ± 30.3 196.7 ± 23.5 197.2 ± 27.3 199.1 ± 25.3 194.9 ± 25.1 LDL-C, mg/dL 116.8 ± 23.1 123.4 ± 20.7 124.3 ± 24.9 126.9 ± 22.6 120.4 ± 21.9 HDL-C, mg/dL 45.2 ± 9.8 43.3 ± 7.4 46.6 ± 8.4 44.2 ± 10.8 48.3 ± 11.1 TG, mg/dL 130.3 ± 78.6 150.5 ± 64.1 131.6 ± 59.6 142.8 ± 80.6 130.7 ± 73.7 FBG, mg/dL 88.4 ± 7.1 88.8 ± 8.2 88.3 ± 6.3 90.8 ± 8.5 87.4 ± 6.3 SBP , mm Hg 118.7 ± 10.1 118.9 ± 11.5 116.4 ± 10.7 120.5 ± 11.1 118.7 ± 11.8 DBP , mm Hg 76.9 ± 7.6 77.2 ± 7.0 76.2 ± 6.4 79.2 ± 6.9 75.8 ± 7.4 Women No. of subjects 64 69 67 56 59 Age, y 47.3 ± 8.0 47.6 ± 7.9 47.1 ± 7.8 46.8 ± 8.3 47.2 ± 8.4 BMI 27.5 ± 5.4 27.9 ± 5.3 28.1 ± 5.4 29.0 ± 5.7 26.1 ± 4.4 V \u02d9 O 2 max, mL/kg/min 22.2 ± 5.0 22.9 ± 4.4 22.9 ± 4.0 23.6 ± 5.1 24.0 ± 4.0 TC, mg/dL 195.0 ± 41.3 189.6 ± 31.8 190.1 ± 32.0 188.3 ± 32.0 180.4 ± 35.2 LDL-C, mg/dL 114.5 ± 31.8 109.1 ± 26.9 112.6 ± 27.9 110.1 ± 27.8 101.8 ± 29.1 HDL-C, mg/dL 58.2 ± 12.2 59.8 ± 14.8 56.9 ± 11.7 58.5 ± 12.2 58.7 ± 12.9 TG, mg/dL 112.4 ± 64.9 102.8 ± 48.7 102.6 ± 51.9 99.4 ± 50.5 100.7 ± 61.7 FBG, mg/dL 85.7 ± 11.5 85.3 ± 7.2 85.1 ± 5.9 86.7 ± 7.4 84.1 ± 6.3 SBP , mm Hg 112.9 ± 11.1 111.1 ± 12.1 112.7 ± 12.4 115.3 ± 12.4 113.9 ± 12.8 DBP , mm Hg 72.9 ± 7.3 70.9 ± 7.3 72.5 ± 7.2 73.5 ± 8.4 72.5 ± 6.8 Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by the square of height in meters); DBP , diastolic blood pressure; FBG, fasting blood glucose; HardI, hard intensity; HDL-C, high-density lipoprotein cholesterol; HiF , high frequency; LDL-C, low-density lipoprotein cholesterol; LowF , low frequency; ModI, moderate intensity; P A, physician advice; SBP , systolic blood pressure; TC, total cholesterol; TG, triglycerides; V \u02d9 O 2 max, maximum oxygen consumption. SI conversion factors: T o convert FBG to millimoles per liter , multiply by 0.0555; to convert HDL-C, LDL-C, and TC to millimoles per liter , multiply by 0.0259; and to convert TG to millimoles per liter , multiply by 0.0113. * Data are given as mean ± SD unless otherwise indicated. There were no significant differences among the 5 conditions ( P \u2b0e .05 for all). For more detailed information, see the \u201cBaseline Characteristics\u201d subsection of the \u201cResults\u201d section. (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2365 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from Table 2. Observed Values for Cardiorespiratory Fitness and for Lipoproteins and Lipids at Baseline and Change From Baseline to 6 Months by Condition Variable Condition * HardI-HiF (n = 86) ModI-HiF (n = 94) HardI-LowF (n = 80) ModI-LowF (n = 73) PA (n = 78) V \u02d9 O 2 max, L/min Baseline 2.09 ± 0.69 2.04 ± 0.59 2.03 ± 0.58 2.20 ± 0.60 2.00 ± 0.55 Change 0.15 ± 0.24\u2020\u2021§ 0.08 ± 0.15\u2020 0.07 ± 0.18\u2020 0.02 ± 0.15 0.04 ± 0.22 TC, mg/dL Baseline 193.4 ± 37.7 192.5 ± 29.2 189.8 ± 28.6 195.4 ± 27.6 186.5 ± 31.4 Change \u22121.3 ± 18.0 0.9 ± 15.9 \u22120.5 ± 16.3 0.4 ± 17.8 \u22120.3 ± 15.0 LDL-C, mg/dL Baseline 115.5 ± 28.4 114.3 ± 26.4 114.5 ± 25.9 118.8 ± 25.5 109.3 ± 26.7 Change \u22122.2 ± 14.4 1.0 ± 14.3 \u22120.8 ± 13.8 \u22121.0 ± 14.5 0 ± 13.7 HDL-C, mg/dL Baseline 52.13 ± 12.21 54.49 ± 14.93 53.47 ± 11.49 54.49 ± 14.93 55.43 ± 13.44 Change 1.83 ± 6.11\u2020\u2021§ 0.54 ± 6.43 \u22120.09 ± 5.55 1.44 ± 6.87 0.03 ± 5.23 TC/HDL-C ratio Baseline 3.89 ± 1.09 3.78 ± 1.09 3.71 ± 0.95 4.02 ± 1.33 3.55 ± 1.02 Change \u22120.12 ± 0.33\u2020\u2021§ 0.04 ± 0.55 \u22120.02 ± 0.46 \u22120.05 ± 0.48 0.02 ± 0.37 TG, mg/dL Baseline 124.8 ± 74.0 119.0 ± 59.4 108.3 ± 52.5 123.9 ± 70.8 108.9 ± 67.1 Change \u22126.9 ± 40.7 8.4 ± 46.6 2.4 ± 29.4 \u22120.2 ± 37.1 \u22122.1 ± 33.3 Abbreviations: See T able 1. SI conversion factors: See T able 1. * Data are given as mean ± SD. The HardI-HiF , HardI-LowF , and ModI-HiF conditions demonstrated significant increases in V \u02d9 O 2 max ( P \u2b0d .01), but only the HardI-HiF condition showed significant improvements in HDL-C level, TC/HDL-C ratio, and V \u02d9 O 2 max, compared with the P A and ModI-LowF groups ( P \u2b0d .01 for each). For more details, see the \u201cCardiorespiratory Fitness\u201d and \u201cLipids, Lipoproteins, and Other Measures\u201d subsections of the \u201cResults\u201d section. \u2020Significant ( P \u2b0d .01) change from baseline. \u2021Significant ( P \u2b0d .01) change compared with the ModI-LowF condition. §Significant ( P \u2b0d .01) change compared with the P A condition. \u2217 10 0 1 2 3 4 5 6 7 8 9 \u2217 \u2020\u2021 \u2217 Increase in Vo 2 max, % A \u2217 10 0 1 2 3 4 5 6 7 8 9 HardI-HiF ModI-HiF HardI-LowF \u2217 \u2020\u2021 \u2217 ModI-LowF PA Condition Increase in Vo 2 max, % B . . Figure. Mean ± SEM change in maximum oxygen consumption (V \u02d9 O 2 max) (measured in liters per minute) from baseline to 6 months (A) and from baseline to 24 months (B) according to treatment condition. At the 6- and 24-month evaluations, the HardI-HiF, HardI-LowF, and ModI-HiF conditions demonstrated significant increases in V \u02d9 O 2 max ( P \u2b0d .01), but only the HardI-HiF condition showed a significant improvement compared with the PA and ModI-LowF groups ( P \u2b0d .01 for each). For more details, see the \u201cCardiorespiratory Fitness\u201d subsection of the \u201cResults\u201d section. HardI indicates hard intensity; HiF, high frequency; LowF, low frequency; ModI, moderate intensity; PA, physician advice; asterisk, a significant change from baseline ( P \u2b0d .01); dagger, a significant change compared with the ModI-LowF condition ( P \u2b0d .01); and double dagger, a significant change compared with the PA condition ( P \u2b0d .01). (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2366 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from combination of HardI plus HiF exercise was the only pre- scription that produced proximal changes in lipopro- tein profile and long-term changes in fitness. The effects of exercise prescriptions on cardiorespira- tory fitness represent an important clinical research is- sue because many of the health benefits associated with increased physical activity are related to changes in fit- ness. 4,5,21,22 Efficacy studies, conducted in closely con- trolled settings, show that supervised training regimens of HardI exercise produce greater improvements in car- diorespiratory fitness than lower-intensity activities. 10 However, to our knowledge, the exercise prescription re- quired to improve fitness in free-living sedentary adults has not been established, due in large part to the vari- ability in adherence that occurs when individuals are counseled to perform unsupervised exercise in their natu- ral environment. 12 Indeed, the amounts of exercise re- corded by our participants, who completed unsuper- vised walking in their home or work environments, were considerably lower than the levels prescribed. During the exercise adoption phase, participants completed approxi- mately 57% to 70% of the minimum amounts pre- scribed. Furthermore, the percentage of prescribed ex- ercise completed varied as a function of intensity, with lower adherence in the HardI groups. Thus, taking the observed adherence levels into account, the significant improvements in cardiorespiratory fitness in this sample were accomplished by the addition of approximately 60 to 90 min/wk of brisk walking or 90 min/wk of leisurely paced walking. Compared with the PA group, significant improve- ments in fitness and lipoprotein outcomes at 6 months were achieved by prescribing the combination of HardI plus HiF exercise. This prescription also resulted in the highest volume of exercise completed. However, be- cause of the nature of our experimental design, wherein intensity and frequency were manipulated while dura- tion was held constant, we did not have a condition that achieved the same volume as the HardI-HiF group through ModI exercise. Consequently, we cannot determine whether the superior performance of this group was be- cause of the combination of HardI-HiF exercise or the greater volume of exercise completed. In a 24-month study of home-based exercise in older adults, King et al 23 con- trolled for volume and intensity of exercise (but not fre- quency or duration), and found greater improvement in fitness for high- vs low-intensity exercise. Our findings suggest that various combinations of in- tensity and frequency may be used to achieve increases in fitness. 12,24 However, when counseling sedentary adults to increase their physical activity, the differential between the amount of exercise prescribed and the amount likely to be completed must be taken into account. Counseling adults to perform 30 min/d of ModI exercise on 3 to 4 d/wk is unlikely to produce a volume of exercise sufficient to reach the threshold required for fitness changes. Consis- tent with the US Surgeon General\u2019s report, 9 our findings suggest that when recommending ModI exercise to free- living adults, a prescription for 30 min/d on 5 d/wk or more seems necessary to achieve measurable benefits. The intensity and frequency of exercise required to produce a favorable response in blood lipids remains un- clear. A review 14 of 28 randomized studies that used ModI to HardI physical activity in interventions of 12 weeks or longer showed a large variability in lipid re- sponse, with significant increases in HDL-C level (mean, 4.6%) observed in approximately 40% of the trials. The HardI-HiF prescription in our study was the only inter- vention to produce a significant proximal effect on HDL-C level (mean, 3.9%) compared with the PA group. Although adherence was lower in the HardI conditions compared with the ModI conditions, the volume of exer- cise was significantly greater in the HardI-HiF vs ModI- HiF condition (6.77 vs 5.02 metabolic equivalent h/wk) and in the HardI-LowF vs ModI-LowF condition (4.00 vs 3.64 metabolic equivalent h/wk). Our findings are simi- Table 3. Intent-to-Treat Values for the Primary Outcomes at Baseline and Change From Baseline to 24 Months by Condition Variable Condition * HardI-HiF (n = 102) ModI-HiF (n = 107) HardI-LowF (n = 97) ModI-LowF (n = 93) PA (n = 93) V \u02d9 O 2 max, L/min Baseline 2.03 ± 0.70 2.02 ± 0.58 1.97 ± 0.54 2.15 ± 0.59 2.01 ± 0.61 Change 0.10 ± 0.21\u2020\u2021§ 0.07 ± 0.20\u2020 0.06 ± 0.20\u2020 0.03 \u2af9 0.17 0.04 ± 0.25 HDL-C, mg/dL Baseline 53.37 ± 12.94 53.94 ± 14.90 53.67 ± 11.81 52.92 ± 13.56 54.87 ± 13.20 Change 0.18 ± 6.59 \u22120.38 ± 5.91 \u22121.14 ± 5.76 \u22120.35 ± 5.64 \u22120.94 ± 5.69 TC/HDL-C ratio Baseline 3.79 ± 1.07 3.80 ± 1.05 3.74 ± 0.94 3.91 ± 1.29 3.57 ± 1.03 Change 0.05 ± 0.45 0.13 ± 0.53 0.07 ± 0.55 0.14 ± 0.53 0.13 ± 0.44 Abbreviations: See T able 1. SI conversion factors: See T able 1. * Data are given as mean ± SD. The HardI-HiF , HardI-LowF , and ModI-HiF conditions demonstrated significant increases in V \u02d9 O 2 max ( P \u2b0d .01), but only the HardI-HiF condition showed a significant improvement compared with the P A and ModI-LowF groups ( P \u2b0d .01 for each). For more details, see the \u201cCardiorespiratory Fitness\u201d and \u201cLipids, Lipoproteins, and Other Measures\u201d subsections of the \u201cResults\u201d section. \u2020Significant ( P \u2b0d .01) change from baseline. \u2021Significant ( P \u2b0d .01) change compared with the ModI-LowF condition. §Significant ( P \u2b0d .01) change compared with the P A condition. (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2367 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from lar to those of Kraus et al, 25 who observed significant in- creases in HDL-C level over 8 months for high-intensity\u2013 high-volume exercise but not for high-intensity\u2013low- volume or low-intensity\u2013low-volume exercise. Thus, changes in HDL-C level may depend on the intensity, frequency, and volume of exercise and on the individu- al\u2019s baseline level. 14,24,25 The effect of the HardI-HiF pre- scription on HDL-C level was not observed at 24 months. As exercise adherence diminished during the 2-year course of the study, the volume of physical activity may have decreased below the threshold required for an ob- servable benefit. 14,24 The seemingly modest long-term changes in cardio- respiratory fitness observed in this study may have prac- tical significance when viewed from a public health per- spective. We observed 2-year fitness changes of 10% or more in 21.2% of the participants prescribed HardI or HiF exercise and in 14.5% of the participants assigned to the ModI-LowF and PA conditions. Findings from the Aerobics Center Longitudinal Study 13 and a related clini- cal trial 17 suggest that a 10% increase in cardiorespira- tory fitness may result in a 15% reduction in mortality. Moreover, significant reductions in coronary events (fatal and nonfatal) accompany changes from the low- est categories of activity/fitness to moderate levels of activity/fitness. 5,13,26 Thus, counseling programs that ef- fectively help sedentary adults adopt regimens of HardI or HiF walking have the potential to produce a benefi- cial impact on the public\u2019s health. Several limitations of this study should be noted. First, the absence of a \u201cno treatment\u201d control group pre- cluded a comparative evaluation of outcome changes in individuals who were advised to make no changes in their physical activity. Because sedentary lifestyle increases the risk of several diseases, we considered it necessary to provide the comparison group with advice to exercise. Second, although the PA group did receive exercise recommendations, the nature of the interven- tion may not parallel the impact of advice delivered indi- vidually by a patient\u2019s personal physician. In addition, while the recommendations in the PA group were simi- lar to those in the ModI-HiF condition, the ModI-HiF group showed a significant improvement in cardiores- piratory fitness, but the PA group did not. This finding suggests the benefits of structured programs of exercise counseling. 27 Third, the long-term return rate in this study (69.5% of participants at 24 months) was some- what lower than the rate observed in other trials (76%- 81% 17,23 ). Because most people who initiate an exercise program fail to maintain exercise over the long run, 28 we considered it reasonable to assume that participants who did not return for follow-up had relapsed to baseline lev- els. Our substitution of baseline data for missing values in the intent-to-treat analyses may represent an overly conservative approach to data analysis. Fourth, our out- comes were limited to changes in fitness and lipopro- teins, and we did not assess changes in health status or the occurrence of clinical events. Finally, individuals with abnormal lipid profiles were excluded from partici- pation, and the restricted range of baseline lipid values may have limited our ability to detect changes as a func- tion of exercise. In conclusion, this study provides important infor- mation about the effects of counseling free-living seden- tary adults to exercise at different levels of intensity and frequency. The findings demonstrate that significant im- provements in cardiorespiratory fitness can be achieved and maintained over 24 months via exercise counseling with a prescription for walking 30 min/d, either at a ModI (45%-55% HRres) 5 to 7 d/wk or at a HardI (65%-75% HRres) 3 to 4 d/wk. Additional benefits, including larger changes in fitness and increases in HDL-C level, may be achieved by prescribing either more exercise or the com- bination of HardI plus HiF exercise. Accepted for Publication: May 13, 2005. Author Affiliations: Department of Epidemiology, Nu- tritional Sciences Program, University of Washington, Se- attle (Dr Duncan); Department of Health Behavior, Pen- nington Biomedical Research Center, Louisiana State University System, Baton Rouge (Drs Anton and New- ton); Department of Psychology, Northern Arizona Uni- versity, Flagstaff (Dr Sydeman); Department of Psychol- ogy, Rush University Medical Center, Chicago, Ill (Dr Corsica); and Departments of Clinical and Health Psy- chology (Drs Durning, Ketterson, and Perri), Physical Therapy (Dr Martin), and Medicine (Dr Limacher), Uni- versity of Florida, and Brain Rehabilitation Research Cen- ter VA RR&D Center of Excellence (Dr Ketterson), Gainesville. Correspondence: Michael G. Perri, PhD, Department of Clinical and Health Psychology, College of Public Health and Health Professions, University of Florida, 101 S New- ell Dr, Gainesville, FL 32610-0185 (mperri@phhp.ufl .edu). Author Contributions: Dr Perri had full access to all the data in the study and takes responsibility for the integ- rity of the data and the accuracy of the data analysis. Financial Disclosure: None. Funding/Support: This study was supported by a Polar Research Award from the American College of Sports Medicine Foundation, Indianapolis, Ind, and Polar Re- search (Dr Duncan); grant R01 HL58873 from the Na- tional Institutes of Health, Bethesda, Md (Dr Perri); and grant RR00082 from the General Clinical Research Cen- ter, National Institutes of Health. Dr Duncan received an American Heart Association/Florida\u2013Puerto Rico Affili- ate Postdoctoral Fellowship (9920174V). Role of the Sponsor: The National Institutes of Health approved the design and conduct of the study. The fund- ing bodies had no role in data extraction and analyses, in the writing of the manuscript, or in the decision to sub- mit the manuscript for publication. Previous Presentation: This study was presented in part at the American College of Sports Medicine\u2019s 49th An- nual Meeting; May 29, 2002; St Louis, Mo; and at the So- ciety of Behavioral Medicine\u2019s 24th Annual Meeting; March 22, 2003; Salt Lake City, Utah. Acknowledgment: We thank our late colleague, Mi- chael L. Pollock, PhD, for his inspiration and guidance in the development of this work; the participants and staff of the Walking Project; and Gary Stevens, PhD, Biosta- tistical Consulting Laboratory, University of Florida, for completing the statistical analyses. (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2368 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from REFERENCES 1. Morris JN, Everitt MG, Pollard R, Chave SP, Semmence AM. Vigorous exercise in leisure-time: protection against coronary heart disease. Lancet . 1980;2:1207- 1210. 2. 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Effects of physi- cal activity counseling in primary care: the Activity Counseling Trial: a random- ized controlled trial. JAMA . 2001;286:677-687. 28. Sallis JF, Haskell WL, Fortmann SP, Vranizan KM, Taylor CB, Solomon DS. Predictors of adoption and maintenance of physical activity in a community sample. Prev Med . 1986;15:331-341. (REPRINTED) ARCH INTERN MED/ VOL 165, NOV 14, 2005 WWW . ARCHINTERNMED.COM 2369 ©2005 American Medical Association. All rights reserved. at Capes Consortia, on April 12, 2011 www.archinternmed.com Downloaded from

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