A total of 4545 telephone screens were conducted and 4081 potential participants were ineligible based on inclusion and exclusion criteria (). After giving informed consent, 464 were randomized, of which 432 had complete QOL data at baseline and 398 of these participants completed the study with 356 usable follow-up QOL surveys. Baseline values were carried forward for missing data/drop-outs, resulting in 430 participants’ data included in the primary analyses. Two participants’ data in the 4 KKW group were eliminated due to being outliers.
CONSORT diagram describing recruitment and retention of participants. *Baseline values were carried forward if follow-up QOL scores were missing.
As summarized in , the study population had a mean (SD) age of 57.4 (6.5), a mean BMI of 31.8 (3.8) kg/m2, and 34.9% were non-Caucasian. Almost 30% of the study population reported a history of depression with 18.2% taking anti-depressant medication at baseline. Only 4.4% of the participants were current smokers and 76.5% were employed. Almost half of the participants were using hormone therapy and 15.2% were taking thyroid medication. With the exception of blood pressure, as a group the cardiovascular risk factors were in normal ranges. The mean baseline peak VO2 was very low at 15.4 (2.9) ml/kg/min (see ). Adherence to exercise was 95.4%, 88.1%, and 93.7% across the 4, 8 and 12 KKW groups and each group spent 73.9, 138.3, and 183.6 minutes per week exercising, respectively ().
Baseline characteristics of the study sample.
Mean (SD) exercise-related variables at baseline and change in exercise-related variables after exercise training.
The mean baseline scores for QOL scales for the total population and by group are presented in . As illustrated in , the DREW sample at baseline had scores similar to the general United States (U.S.) population20
. The mean QOL scores for the DREW sample differed from the national mean by only 0.02 to 0.22 standard deviation units, which are considered differences of small magnitude 21
. The mean baseline scores for QOL scales across specific subgroups are presented in , and, although some comparisons had small sample size, these data demonstrate that we observed many of the expected QOL differences among groups. For example, QOL at baseline was lower on all scales among participants taking antidepressant medication compared to participants not taking such medication. Additionally, employed participants reported better QOL on the PF, RP, and BP scales.
Figure 2 Mean (± SD) baseline SF-36 scores for the DREW sample and the national mean for the United States. The mean QOL scores for the DREW sample differed from the national mean by only 0.02 to 0.22 standard deviation units, which are considered differences (more ...)
Unadjusted fitted mean (SD) baseline quality of life (SF-36) scores by subgroups.
summarizes the mean change in SF-36 measures across the control and exercise groups. The positive linear trend across groups was statistically significant for all physical and mental QOL scales (all p-values < 0.0001), with exercise dose being a significant independent predictor of change in all QOL scales (p-values ranged from < 0.0001 to 0.04), except bodily pain (p=0.19). Thus, a dose-response effect of exercise on QOL was noted for all aspects of QOL except bodily pain. The ANCOVAs indicated that for all physical and mental QOL scales, except BP (p=0.32), the 12 KKW group significantly improved QOL compared to the control (p-values ranged from <0.001 to 0.04). Additionally, the 4 KKW group significantly improved GH, VT, and MH compared to control (p-values 0.01 to 0.04). All three exercise groups significantly improved SF compared to control (p-values < 0.0001 to 0.03). The analyses were conducted without the aforementioned covariates and the results were virtually identical.
Figure 3 Mean change (Least-squares means ± 95% confidence interval) on SF-36 measures across the control and exercise groups. The dose-response relations between exercise dose and change in QOL were evaluated with regression analysis to test for trends (more ...)
The mean change in weight across the control, 4 KKW, 8 KKW and 12 KKW groups was -0.94 (4.0), -1.34 (3.5), -1.86 (3.4), and -1.34 (2.9) kg, respectively, with no between group differences. To examine the effect of weight loss on improvement in SF-36 measures, all analyses were repeated with additional adjustment for change in body weight. Weight change was a significant covariate in only two of the eight comparisons and inclusion of this covariate did not have a meaningful effect on any of the mean values, significance, nor trends across exercise groups. To further assure that weight loss was not responsible for the observed results, change in SF-36 scores across the exercise groups was examined with participants sub-grouped into those who lost weight and those who maintained or gained weight. summarizes the change in SF-36 scores across exercise groups for these subgroups. The p-values for the treatment-by-subgroup interactions for the SF-36 scales ranged from 0.07 to 0.95. These non-significant interactions indicate that the pattern of change in each of the SF-36 measures across the exercise groups was similar for those who did and did not lose weight.
Figure 4 Change in SF-36 scores across the exercise groups was examined for two subgroups of participants: 1) those who lost weight vs. 2) those who maintained or gained weight, using analysis of covariance (ANCOVA) with baseline age, antidepressant use, employment (more ...)
All analyses were repeated with change in fitness as a covariate, and the conclusions from these analyses were not meaningfully affected. Change in fitness was also correlated with change in QOL and only two of the eight correlation coefficients differed significantly from zero and the size of the coefficients was small (Physical Functioning, r=.11, p=.02; Role Physical, r=.12, p=.02). These findings suggest that changes in fitness are not necessary to improve QOL when individuals increase physical activity.
To explore the effect of antidepressant use on the results, participants were sub-grouped by antidepressant use (yes/no), and change in QOL among exercise groups was tested with an exercise group by sub-group interaction. The interaction term was not significant for all four physical measures of QOL (p-values > .11), but it was significant for the Role Emotional, Social Functioning, and Vitality scales (the p-value for the Mental Health scale approached significance; p=.06). These findings and examination of group means indicated that participants in the non-exercise control condition who took antidepressant medication experienced no increase in QOL during the trial, and for some mental QOL measures they experienced decreased QOL. Conversely, control participants who were not taking antidepressant medication experienced small increases in QOL during the trial.