Purpose: Exercise adherence is difficult during cancer treatments, but few studies have examined the predictors of such exercise. Here, we report the predictors of adherence to supervised exercise training during breast cancer chemotherapy.
Methods: Breast cancer patients (N = 242) initiating adjuvant chemotherapy in Edmonton, Ottawa, and Vancouver were randomly assigned to usual care (n = 82), supervised resistance exercise (n = 82), or supervised aerobic exercise (n = 78) for the duration of their chemotherapy. Baseline data on standard demographic, medical, behavioral, fitness, and psychosocial variables as well as motivational variables from the Theory of Planned Behavior were collected. Adherence was assessed by objective attendance records.
Results: Adherence to supervised exercise was 70.2%. Univariate analyses indicated significant or borderline significant associations between exercise adherence and location/center (r = 0.30; P < 0.001), V˙O2peak (r = 0.21; P = 0.008), muscular strength (r = 0.21; P = 0.008), percent body fat (r = −0.21; P = 0.012), disease stage (r = 0.17; P = 0.031), education (r = 0.15; P = 0.053), depression (r = −0.14; P = 0.073), and smoking (r = −0.14; P = 0.081). In multivariate analysis, location/center (β = 0.28; P = 0.001), V˙O2peak (β = 0.19; P = 0.016), disease stage (β = 0.18; P = 0.015), and depression (β = −0.16; P = 0.033) remained significant and explained 21% of the variance in exercise adherence. Participants in Vancouver, with higher aerobic fitness, more advanced disease stage, and lower depression, achieved better adherence.
Conclusion: Adherence to supervised exercise training was predicted by unique aspects of the location/center, disease stage, aerobic fitness, and depression but not motivational variables. Location/center in our trial may have been a proxy for the amount of one-on-one attention received during supervised exercise. These findings may have implications for improving adherence during breast cancer chemotherapy.