Attrition and adherence of young women to aerobic exercise: lessons from the WISER study

The purpose of this report is to identify factors associated with attrition and adherence of young women to a 16-week randomized aerobic exercise intervention on biomarkers associated with breast cancer risk. The exercise group was prescribed a progressive weight-bearing aerobic exercise program consisting of 30 minute workouts, 5 times/wk for 16 weeks. Adherence was calculated as the average minutes of exercise per week during participation in the study. Of the total of 212 women randomized into the exercise intervention 46 dropped out, of which 82.5% dropped out during the earlier stages of exercise suggesting that reasons for withdrawal may have been related to difficulties with initiating physical activity. Time commitment or lack of time was the primary reason for withdrawal. Drop outs reported lower physical activity at baseline than study completers (p=.0007). Although 78% of the 212 randomized participants completed the exercise intervention, only 4.7% of the participants exercised for at least 150 min/wk during the entire study period. Significant predictors of adherence were self-reported physical activity at baseline and depression scores. We conclude that predictors of adherence to exercise in our population of young women are similar to those reported for older adults. We also found that young women are more likely to exercise at moderate to vigorous intensity for 90 to 120 min rather than 150 min per week, even when participating in a highly structured exercise intervention.