Construct Validity of the Steep Ramp Test for Assessing Cardiorespiratory Fitness in Patients With Breast Cancer and the Effect of Chemotherapy-Related Symptom Burden

Objective: To investigate the construct validity of the Steep Ramp Test (SRT) by longitudinally comparing the correlation between maximum short exercise capacity of the SRT and direct measurements of peak oxygen consumption (VO₂peak) during or shortly after treatment in patients with breast cancer and the potential effect of chemotherapy-induced symptom burden. Design: Cross-sectional. Setting: Multicenter. Participants: We used data from 2 studies that included women with breast cancer treated with chemotherapy, resulting in 274 observations. A total of 161 patients (N=161) performed the cardiopulmonary exercise test and the SRT in 2 test sessions on different time points around chemotherapy treatment. Interventions: Not applicable. Main Outcome Measures: Fatigue was assessed with the Multidimensional Fatigue Inventory, and nausea and vomiting and pain by the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30. The longitudinal correlation between the maximum short exercise capacity and VO₂peak was investigated using a linear mixed model. Interaction terms were added to the model to investigate whether the correlation varied by symptom burden. Results: We found a statistically significant moderate correlation between VO₂peak and maximum short exercise capacity (0.61; 95% confidence interval, 0.51-0.70; P<.01) over time. This correlation was slightly attenuated (−0.07; 95% confidence interval, −0.13 to 0.00; P=.04) in patients with chemotherapy-related nausea and vomiting, indicating smaller correlations of VO₂peak with the maximum short exercise capacity with increasing symptom burden. Pain and fatigue did not significantly modify the correlation. Conclusions: The SRT can only be used as a proxy for changes in aerobic capacity with great caution and with attention for the level of nausea and vomiting.