Few studies have examined the predictors of adherence separately for supervised and unsupervised exercise or in postmenopausal women over an extended time period. Here, we report the predictors of exercise adherence in the Alberta Physical Activity and Breast Cancer Prevention (ALPHA) Trial.
The ALPHA trial randomized 160 postmenopausal women in Calgary and Edmonton, Canada to an exercise intervention that consisted of an average of 200 min/wk of supervised (123 minutes) and unsupervised (77 minutes) exercise over a 1-year period. Baseline data were collected on demographic, health-related fitness, quality of life, and motivational variables from the theory of planned behavior.
Participants completed an average of 95% of their supervised exercise and 79% of their unsupervised exercise. In multivariate analyses, 8.1% (P = .001) of the variance was explained for supervised exercise by being from Edmonton (β = 0.22; P = .004) and older (β = 0.15; P = .050). For unsupervised exercise, 21.1% (P < .001) of the variance was explained by being from Calgary (β = –0.39; P < .001), having a family history of breast cancer (β = 0.21; P = .003), and having higher vitality (β = 0.19; P = .011).
Predictors of adherence may differ for supervised and unsupervised exercise, moreover, predicting adherence to supervised exercise may be particularly difficult in well-controlled efficacy trials.
Courneya is with the Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada. Karvinen is with the Dept of Exercise Science, East Carolina University, Durham, NC. McNeely is with the Dept of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada. Campbell is with the Dept of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada. Brar and Friedenreich are with the Dept of Population Health, Alberta Health Services, Calgary, Alberta, Canada. Woolcott is with the Dept of Epidemiology, Dalhousie University, Halifax, Nova Scotia, Canada. McTiernan is with the Prevention Center, Fred Hutchinson Cancer Research Center, Seattle, WA. Ballard-Barbash is with the Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MA.