RESUMEN
Breast cancer survivors (BCS) have a high prevalence of cardiovascular disease and low cardiorespiratory fitness (CRF). CRF is an important predictor of survival in BCS. However, the physiological factors that contribute to low CRF in BCS have not been completely elucidated. To assess differences in physiological factors (cardiac, pulmonary, muscle function) related to CRF between BCS and controls. Twenty-three BCS and 23 age-body mass index (BMI) matched controls underwent a peak cycling exercise test to determine CRF, with physiological factors measured at resting and at peak exercise. Cardiac hemodynamics (stroke volume [SV], SVindex, heart rate [HR], cardiac output [Formula: see text], and [Formula: see text]index) were evaluated using ultrasonography. Pulmonary function was evaluated using the oxygen uptake efficiency slope (OUES), ventilation to carbon dioxide production slope [Formula: see text] and breathing reserve at peak exercise (BR). Muscle oxygenation variables (oxygenated [HbO2] deoxygenated [HHb] and total hemoglobin [Hb], and tissue oxygenation index [TSI]) were measured with near-infrared spectroscopy (NIRS). Both groups had similar CRF and similarly increased all hemodynamic variables (HR, SV, SVindex, [Formula: see text] and [Formula: see text]index) at peak exercise compared to resting (p < 0.001). BCS had higher overall HR and lower SVindex (group effect, p < 0.05). BCS had similar OUES, [Formula: see text] and BR compared to the controls. Both groups decreased TSI, and increased Hb and HHb similarly at peak exercise compared to resting (p < 0.001). Our data suggest BCS do not exhibit differences in cardiac, pulmonary, or muscle function at peak exercise compared to controls, when both groups have similar CRF and physical activity.