People with obesity have varying degrees of cardiovascular, pulmonary, and musculoskeletal dysfunction that affect aerobic exercise testing variables. Short time after bariatric surgery, these dysfunctions could affect both peak oxygen consumption ([Formula: see text] O2 peak), the gold standard for assessing cardiorespiratory fitness (CRF) and aerobic capacity evaluated with ventilatory threshold (VT1). The purpose of this study was to evaluate the short-term effect of bariatric surgery, i.e. before the resumption of physical activity, on submaximal, at VT1 and maximal cardiorespiratory responses in middle-aged women with severe obesity. Thirteen middle-aged women with severe obesity (age: 36.7 ± 2.3years; weight: 110.5 ± 3.6kg, BMI: 41.8 ± 1.1kg/m2) awaiting bariatric surgery participated in the study. Four weeks before and 6 to 8weeks after surgery, body composition was determined by bioelectrical impedance. The participants performed an incremental cycling test to [Formula: see text] O2 peak. After bariatric surgery, all body composition parameters were reduced, absolute [Formula: see text] O2 peak and peak workload decline with a lower VT1. Relative [Formula: see text] O2 at peak and at VT1 (ml/min/kg or ml/min/kg of FFM) remained unchanged. Ventilation was lower after bariatric surgery during exercise with no change in cardiac response. Our results showed that weight loss alone at short-term after bariatric surgery decreased CRF as seen by a decrease in absolute [Formula: see text] O2 peak, and peak workload with lower VT1, whereas relative [Formula: see text] O2 (ml/min/kg or ml/min/kg of FFM) during exercise remained unchanged in women with obesity. Rapid FFM loss affects cardiorespiratory responses at submaximal and maximal.