Evaluating tests of physical function as surrogate markers of cardiorespiratory fitness in early-stage breast cancer survivors

Background: Breast cancer is the most prevalent type of cancer in women. Currently there are more than 4 million women in the U.S. living with breast cancer and beyond (i.e., breast cancer survivors). Breast cancer survivors are at risk for developing cardiovascular disease. Cardiorespiratory fitness, assessed by the gold standard method of peak oxygen consumption (VO 2 peak) during a maximal exercise test, is an independent predictor of cardiovascular disease mortality. However, assessing VO2peak is often limited in breast cancer survivors due to cancer- and cancer-treatment related challenges (e.g., fatigue, muscle weakness, and other physical and psychological barriers) as well as practical and technical limitations (e.g., cost of VO2peak assessment, expensive equipment, and skilled personnel). Therefore, the purpose of this study was to investigate whether relatively simple tests of physical function may serve as surrogate markers of cardiorespiratory fitness in women with early-stage breast cancer. Methods: Thirty-two women with breast cancer stage I to III (age: 60 ± 11 years; body mass index (BMI): 27 ± 6 kg/m 2 ; mean ± SD) who had completed primary cancer treatment participated in this study. VO2peak was assessed using open circuit spirometry during a customized modified Balke treadmill test. Physical function was assessed using the 6-minute walk test (6MWT), timed up-and-go (TUG), and the 30-second chair stand test (30CST). Fatigue was self-reported using the Functional Assessment of Chronic Illness Therapy–Fatigue questionnaire. Pearson correlations were used to examine the relationship of VO 2 peak with functional assessments and fatigue. Additionally, functional assessments, fatigue, age, and BMI were evaluated as predictors of VO2peak using backward stepwise linear regression. Results: Higher VO 2 peak was associated with longer 6MWT distance (r=0.62, P< 0.001) and shorter TUG time (r=-0.45, P=0.01). However, the correlations between VO 2 peak and the 30CST performance or fatigue did not reach statistical significance (r=0.30 and r=-0.28, P=0.1). Based on backward stepwise regression analysis, 6MWT distance, age, and BMI were independent predictors of VO2peak while fatigue and performance on 30CST and TUG time were not retained in the model. Conclusions: Among breast cancer survivors, better physical function was associated with higher cardiorespiratory fitness. Larger studies are needed to establish the utility of performance on physical function tests as surrogate markers of cardiorespiratory fitness. Additionally, exercise interventions should investigate whether improvements in physical function are predictive of improvements in cardiorespiratory fitness. Support was provided by the University of Florida Health Cancer Center Pilot Grant # CA-FY22-05. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.