Potential for Cardiovascular Exercise Dosing to Improve Cardiorespiratory Fitness in Breast Cancer Survivors

Abstract

With an increase in early detection and curative treatment for breast cancer, there is a growing number of breast cancer survivors. Cancer survivors are at greater risk than their age matched peers for long-term health sequelae including recurrence of primary tumors and cardiovascular disease (CVD). Besides the direct effects of cancer treatment and a genetic predisposition, lifestyle factors are believed to contribute to these comorbid conditions. Despite knowing the benefits associated with an active lifestyle, breast cancer survivors have reported to decrease their activity level by as much as two hours or more per week, based on their treatment regimen. Guidelines for diet and/or exercise targeting cancer survivors have been proposed, but a paucity of data is available on optimal interventions for improving lifestyle behavior change in this population. This dissertation was undertaken to address important unanswered questions. Specifically, can prescribed home-based exercise dosing be performed in a safe and effective manner during a combined diet and exercise intervention? And, will cardiovascular exercise dosing help improve selected outcomes of interest for breast cancer survivors? Initially, we performed a cross-sectional study to investigate the cardiorespiratory fitness (VO2max) level and body composition (weight, BMI, % body fat) in breast cancer survivors. We reported that breast cancer survivors had a low VO2max compared to normal values in a healthy population. In addition, submaximal VO2 exercise testing on a treadmill and elliptical trainer had a strong correlation to the gold standard test for measuring cardiorespiratory fitness on a treadmill. Next, we undertook study to investigate the feasibility of using cardiovascular exercise dosing during a 17 week combined diet, home-based exercise, and behavior modification intervention. For simplicity, we will refer to this 17 week intervention as the "Energy Balance Program" throughout the remainder of this dissertation. In addition to investigating feasibility, we analyzed the potential for cardiovascular exercise dosing to have different effects on CVD and breast cancer risk factors including low VO2max and weight gain during an Energy Balance Program. Nineteen female breast cancer survivors participated in an Energy Balance Program. One cohort received "usual care" cardiovascular exercise instructions including moderate continuous exercise (MCT) and a second cohort was prescribed cardiovascular exercise dosing in the form of interval training (IT). Both groups reported significant improvements in VO2max and body composition. Additionally, the IT group had a significantly greater improvement in VO2max compared to MCT, without any cardiovascular related adverse events (AE). In conclusion, we were able to demonstrate a high correlation between sub-maximal and maximal exercise testing using both the treadmill and arc trainer in breast cancer survivors at high risk for CVD. In addition, breast cancer survivors in our study had a low VO2max, but were able to successfully participate in a home based exercise and weight loss program, resulting in significant improvements in body composition and VO2max, with significantly greater improvements in the IT versus MCT group for VO2max.