Determination of the effects of different constant load exercise tests on body metabolism and substrate utilisation

Body substrate utilization was examined comparatively in 5 different constant load exercise tests to find optimal fat burning zone. Seven sedentary male subjects participated in the study after giving signed written informed contents, which were approved by the local ethical committee. They initially performed an incremental exercise test (15 W/min) for estimation of anaerobic threshold (AT), respiratory compensation point (RCP) and maximal exercise capacity (Wmax) using cycle ergometer. Then, each subject performed 5 different constant load exercise tests (30 min): work load corresponded to 25% below AT, at the AT, at the RCP, at the 25% above AT and at 100% above AT. Ventilatory and pulmonary gas exchange parameters were evaluated breath-by-breath. Metabolic changes were determined using respiratory quotient (RQ). AT and RCP were estimated using V-Slope method and other conventional methods. A paired t- test was used to evaluate values. Fat oxidation ratio was found to be higher in RCP (0.917±0.04) than AT (0.950±0.02) and 25% below AT (0.952±0.01) (p<0.05). RQ was systematically increased workload at the 25% above AT (1.046±0.03) and at 100% above AT (1.530±0.09). Increasing exercise intensity (from 25% below to AT to RCP) caused increases in fat oxidation ratio. However, workload intensity above the RCP results in increases carbohydrate oxidation rate due to the anaerobic glycolysis. Increases in fat oxidation at the workload at corresponded to RCP could be an important training protocol for clinical medicine.Key Words: Exercise Test, Metabolism, Anaerobic Threshold, Respiratory Quotient.