Exercise Duration and Intensity in a Weight-Loss Program

Objective: To examine the effect of duration and frequency of exercise on weight loss and cardiorespiratory fitness in previously sedentary, overweight, women. Design: Randomized, controlled, 4-arm trial of 12-months duration. Setting: A university-based behavioral weight loss program during the years 2000 and 2001. Participants: Eligibility criteria were: women, 21 to 45 years of age, body mass index (BMI) 27 to 40, reporting exercise <3 days/week for <20 minutes/day during the previous 6 months. Exclusion criteria were: a history of myocardial infarction, taking medication that would alter the heart rate response during exercise or that would affect metabolism or weight loss, being treated for psychologic conditions, pregnant, recently pregnant, or planning pregnancy, having a medical condition that could affect metabolism or body weight (eg, diabetes) or that would limit exercise participation. Intervention: All 201 participants were assigned to a standard behavioral weight loss program, which included regular group meetings and telephone calls, and caloric and dietary fat restrictions. Participants were given meal plans and kept weekly food diaries. The women were assigned to 1 of 4 exercise groups based on energy expenditure of 1000 kcal/wk or 2000 kcal/wk and exercise intensity (moderate versus vigorous). Exercise intensity was prescribed according to percentage of age-predicted maximal heart rate and rating of perceived exertion. Energy expenditure was converted to minutes of exercise per week. The groups were vigorous intensity/high duration, moderate intensity/high duration, moderate intensity/moderate duration, and vigorous intensity/moderate duration. All 4 groups started the program at moderate intensity and moderate duration (100 min/week of walking) and increased the vigor and duration of exercise to set targets of 200, 300, 200, and 150 min/week, for the groups respectively. Treadmills were provided to the participants, and feedback on their weekly exercise logs was given. Main outcome measures: At 6 and 12 months, changes in body weight and BMI were measured. Cardiorespiratory fitness was measured by a graded exercise treadmill test and expressed as percent change in oxygen consumption from baseline. Excluding 5 women who left the study (because of pregnancy or death) the data were analyzed by the intention-to-treat method (completion rate 184/196 = 94%). Main results: Attendance at group sessions and reported dietary intake and exercise adherence suggested that all groups complied similarly with their dietary and exercise prescriptions. Mean weight loss after 1 year was 8.9, 8.2, 6.3, and 7.0 kg, for the vigorous intensity/high duration, moderate intensity/high duration, moderate intensity/moderate duration, and vigorous intensity/moderate duration groups, respectively, but there was no effect of exercise duration or exercise intensity on changes in body weight or in BMI. Cardiorespiratory fitness increased for all groups; 22%, 14.9%, 13.5%, and 18.9%, for the vigorous intensity/high duration, moderate intensity/high duration, moderate intensity/moderate duration, and vigorous intensity/moderate duration groups, respectively, but the groups did not differ in effect of exercise intensity (P = 0.11) or exercise duration (P = 0.35). When participants were divided by their reported average weekly duration of exercise at months 6 and 12, the group which averaged ≥200 min/week at both time points lost more weight than the groups which averaged <150 min/week of physical activity or whose activity duration was inconsistent (difference among groups, P = 0.01). They also had a greater percent increase in cardiorespiratory fitness than those who averaged <150 min/week of physical activity (P = 0.007) and those whose activity was inconsistent (P = 0.003). Conclusion: Sedentary overweight women lost weight and improved cardiorespiratory fitness in a year-long combined dietary and exercise regimen. Duration of exercise (at least 150 min/week of walking) was more important than vigorous versus moderate intensity in achieving these goals.