Cardiopulmonary exercise test (CPET)
The CPET was performed using the Vyntus CPX (Carefusion, Germany) linked to a gas analysis system (CardiO2 System; Medical Graphics Corporation, MN, USA). The adolescents performed a ramp-symptom-limited CPET consisting of 2 minutes (min) of rest, 3 min of warm-up (unloaded pedaling), and an incremental work period (15 W/min for height < 150 cm and 20 W/min for height ≥ 150 cm) (7). During the test, the adolescents were instructed to continue pedaling at 60 rpm. The test was set to last from 8 to 12 minutes until 90% of the maximal heart rate (HR) predicted was reached, and 1.10 of the respiratory exchange rate (RER) was considered available (7). Oxygen saturation (SpO2) was measured via pulse oximetry (Onyx, model 9500; Nonin, Plymouth, MN), and the electrocardiography signals (Welch Allyn CardioPerfect, Inc., NY) were monitored continuously during the tests. The following variables were recorded: power, peak oxygen uptake (VO2peak), minute ventilation (VE), carbon dioxide production (VCO2), RER, and HR. Additionally, blood pressure, the Borg score for leg discomfort, and severity of dyspnea were measured at rest and every 2 min during the test until the end of the test (19). Males and females were considered to have aerobic fitness when they reached VO2peak ≥ 43.4 and ≥ 35.6 ml/kg/min, respectively. If these thresholds were not met, they were considered to have low aerobic fitness (20). The tests were performed in accordance with the American Thoracic Society recommendations. The predicted CPET values were calculated for a Brazilian population (21).