Effects of Difference Doses of Physical Activity on Cardiorespiratory Fitness Among Sedentary, Overweight or Obese Postmenopausal Women With Elevated Blood Pressure: A Randomized Controlled Trial

Church TS, Earnest CP, Skinner JS, Blair SN. JAMA. 2007;297:2081-2091.

Levels of cardiorespiratory fitness are inversely related to risk of both cardiovascular disease (CVD) and all-cause mortality. Moreover, improvements in fitness have been shown to reduce mortality risk. In the US, 1 in 3 women are postmenopausal, and 30% of this group report no physical activity, putting them at increased risk for CVD and other chronic diseases. The National Institutes of Health (NIH) Consensus Development Panel recommendation is commonly used to prescribe physical activity for promoting general health. This study, called the Dose-Response to Exercise in postmenopausal Women (DREW) trial, examined the effect of 50%, 100%, and 150% of the NIH Consensus Panel physical activity recommendation on cardiorespiratory fitness in sedentary, postmenopausal overweight or obese women.

A total of 4545 telephone screening interviews were performed, and after filing informed consent, 464 postmenopausal women 45 to 75 years of age who were not exercising > 20 minutes per day more than twice a week and taking < 8000 steps per day over 1 week, were overweight or obese (body mass index [BMI] 25-43), and had systolic blood pressure (BP) 120 to 160 mm Hg were randomly assigned to a nonexercise control group (n = 102) or energy-expenditure group of either 4 (n = 155), 8 (n = 104), or 12 (n = 103) kcal/kg/week .Women in the control group maintained their levels of activity and recorded their daily steps throughout the 6-month study period. Exercising women participated in 3 or 4 training sessions each week for 6 months at a heart rate associated with 50% of each woman“s peak VO_2. Weekly, all participants were weighed, and the number of calories expended by each patient was calculated. All exercise sessions were performed under observation and supervision in exercise training laboratories, and during nonsupervised physical activity, all participants wore step counters. Other assessments included height, smoking history, medication usage, diet, and BP. After a 30-minute rest period, BP was measure while participants were in recumbent position, and a minimum of 4 readings were taken 2 minutes apart. The primary study endpoint was aerobic fitness assessed on a cycle ergometer that was quantified as peak absolute oxygen consumption (VO₂abs, L/m). Secondary outcomes included peak relative oxygen consumption (mL/kg/m; VO₂rel) and peak power output quantified in watts (Wpeak).

At baseline, the participants were a very low-fit group, with mean ± SD age of 57.3 ± 6.4 years, BMI = 31.8 ± 3.8, systolic BP = 139.8 ± 12.9, respiratory exchange ratio = 1.13 ± 0.07, very low VO₂abs and VO₂rel 1.30 ± 0.25 L/m and 15.5 ± 2.8 mL/kg/m, respectively. They had fasting glucose levels and lipid profile (including LDL cholesterol, HDL cholesterol, and triglyceride) within acceptable clinical ranges. After 6 months of exercise intervention, the 4-, 8-, and 12-kcal/kg/week group obtained 72.2 ± 12.3, 135.8 ± 19.5, and 191.7 ± 33.7 minutes per week over 2.6 ± 0.3, 2.8 ± 0.4, and 3.1 ± 0.5 sessions. The average maximal metabolic equivalent tasks (METs) during the cycle ergometer training were similar across all groups at 3.8. In comparison, METs during the treadmill training among the 4-kcal/kg/week group were 3.1 ± 0.6, in the 8-kcal/kg/week were 3.3 ± 0.6, and in the12-kcal/kg/week group were 3.5 ± 0.8. Exercise adherence among the randomization groups ranged from a high of 94.6% in the 4-kcal/kg group to a low of 89.0% in the 8-kcal/kg group, whereas the adherence increased to 97% in all groups when only study completers were examined. Only 4 individuals from the 8-kcal/kg/week group dropped out due to injuries, 1 of which was job related, and the other 3 were the results of preexisting conditions.

At baseline all 4 groups averaged 5000 (range 4741-5039) daily steps. After 1 month, the number of daily steps with the 3 exercise groups ranged from 5291 to 5377 compared to 6063 in the control group (P < .05 for each vs baseline). At Month 1 the control group had more steps per day than the 3 exercise groups (P < .05 for each comparison); however, by Months 5 and 6 there were no statistically significant differences between the 4 groups. There were no differences in mean daily steps for Months 1 through 6 among the 3 exercise groups. Among all 3 fitness measures, each exercise dose had significantly higher fitness values than did the control group (P < .001 for each). In addition, the linear trend across the exercise groups was significant (P < .001). There were no differences in weight, body fat percent, or CVD risk factors across the groups; however, there was significant difference in waist circumference between the 3 exercise groups and control (P < .05 for each). The energy intake for the control group was 1970 ± 791, the 4-kcal/kg/week group was 1879 ± 727, the 8-kcal/kg/week group was 2041 ±Â­ 937, and the 12-kcal/kg/week group = 1960 ± 803, and the between-group differences were not significant (P = .56).

The analysis of variance was significant for systolic BP (P = .03), with the only significant between-group difference found when comparing 4- and 12-kcal/kg/week groups (P = .02). Although there were no significant between-group differences in systolic BP ≥ 140 mm Hg at baseline or follow-up between the groups, within the 12-kcal/kg/week (48.5 vs 36.9%, P = .01) and control groups (54.9 vs. 43.1%, P = .05) the prevalence at follow-up was significantly lower than at baseline. Although there were no significant between-group changes in systolic BP, there was a significant change within the 12-kcal/kg/week group (-3.3 mm Hg; P = .003). There were no statistically significant changes in BP medication use among the groups nor between-group differences in diastolic BP.

The mean percent change in fitness data VO₂abs, VO₂rel, and Wpeak were adjusted for age, ethnicity/race, weight, and peak heart rate. Compared with the control group, VO₂abs increased by 4.2%, 6.0%, and 8.2% in the 4-, 8-, and 12-kcal/kg/week groups, respectively. The VO₂rel percent change was similar across the 3 exercise groups, equating to 4.7%, 7.0%, and 8.5%. The Wpeak also increased by 7.6%, 10.7%, and 12.9% in the 4-, 8-, and 12-kcal/kg/week groups, respectively. Each P value for pairwise comparisons of control within each exercise group was significant (P < .001) for every fitness measurement, as were linear trends (P < .001 for all 3 fitness measures. The P values for treatment x subgroup interactions were not significant, suggesting similar changes in fitness across all 3 training groups.

Data obtained form this study demonstrate a strong (P < .001) dose-response relation between the amount of exercise and change in fitness. However, there were no significant changes observed in CVD risk factors that were measured, including weight or body fat percentage, lipid profile, and BP. The exercise group did benefit from a decrease in waist circumference, which is of clinical importance given the association between excess abdominal adiposity and increased risk of insulin resistance, diabetes, metabolic syndrome, and mortality. The trial supports the notion that even moderate-intensity physical activity of 72 minutes per week can significantly improve fitness in previously sedentary postmenopausal women. In addition, similarity in the physical activity-fitness dose-response relation across ethnic/racial groups, age, weight, baseline fitness, and hormone therapy subgroups provides evidence that physical activity has similar benefits for all individuals.