The Maximum Symptom-Limited Cardiopulmonary Exercise Test (CPET), the gold standard method for assessing cardiorespiratory fitness, will be performed on a bicycle ergometer (Corival CPET, Lode, Groningen, Netherlands). During the test, the bicycle ergometer ramp test protocol will be applied (starting workload = 20 W / 20W increase every three minutes / maintaining a rotation speed of 60-70 rpm) (2). During the CPET, heart rate (HR) and heart rhythm will be continuously monitored with a 12-channel ECG test system (Custo Cardio 200 BT system, CustoMed GmbH, Ottoburn, Germany).