Predictors of Adherence in a Randomized Controlled Trial of Exercise in Prostate Cancer Survivors

Abstract

1580 We conducted a randomized controlled trial designed to determine the effects of a 12 wk supervised resistance exercise training (RET) program on muscular strength, fatigue, and quality of life (QOL) in prostate cancer survivors receiving androgen deprivation therapy. We previously reported statistically significant and clinically meaningful changes in trial end points in favor of the exercise group. We also reported a 78.3% adherence rate to the intervention. PURPOSE: To examine predictors of exercise adherence in the trial. METHODS: Prostate cancer survivors (N = 155) completed measures of demographic, social cognitive, QOL, behavioral, and fitness variables before being randomized to either an exercise (n = 82) or control (n = 73) group. The exercise group was asked to perform supervised RET 3/wk for 12 wks. The control group was asked not to initiate RET. RESULTS: The exercise group attended 28.2 (78.3%) of the 36 sessions. Univariate analyses revealed eight statistically significant (ps <.05) predictors of exercise adherence during the trial including exercise stage of change, intention, age, QOL, fatigue, subjective norm, leg press test, and perceived behavioral control. A multivariate analysis indicated that there were three independent predictors of trial adherence that explained 20.4% of the variance: exercise stage of change (β = .26; p = .013), age (β = −.22; p = .037), and intention (β = .19; p = .073). Ancillary analyses indicated that the control group performed significantly more aerobic exercise outside of the trial than the exercise group (p = .020). This difference resulted from a significant decline in nonprogram-related aerobic exercise in the exercise group (p = .001) rather than an increase in the control group (p = .945). CONCLUSION: Exercise adherence in the trial was very good but not optimal. Moreover, the exercise group partly compensated for their RET program by reducing their nonprogram-related aerobic exercise. Adherence was predicted by variables from many different categories including social cognitive, QOL, behavioral, fitness, and demographic. These findings may have important implications for maximizing adherence during clinical trials of exercise in prostate cancer survivors. Supported by the National Cancer Institute of Canada