Predictors of adherence to supervised and unsupervised exercise in the Alberta Physical Activity and Breast Cancer Prevention Trial.

BACKGROUND 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. METHODS 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. RESULTS 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). CONCLUSIONS 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.