Objective: Body substrate utilizations were examined comparatively in various constant load exercise tests to find optimal fat burning zone.

Material and Methods: Seven sedantery male subjects participated to the study after giving signed written informed consents which were approved by the local ethical committee. They initially performed an incremental exercise test (15 W/min) for estimation of anaerobic threshold (AT) and maximal exercise capacity (Wmax) using cycle ergometer. Then, each subject performed 3 different constant load exercise tests (30 min): work load corresponded to 25% below AT, at the AT, and at the 25% above AT. Ventilatory and pulmonary gas exchange parameters were evaluated breath-by-breath. Metabolic changes were determined using respiratory quotient (RQ). AT was estimated using V-slope and other conventional methods. A paired t- test was used to evaluate values.

Results: Fat oxidation ratio was found to be 0.950±0.02 in AT and 0.952±0.01 in 25% below AT. RQ systematically increased work load at the 25% above AT (1.046±0.03).

Conclusion: Increasing exercise intensity (from 25% below AT to AT) caused increases in fat oxidation ratio. However, the work load intensity 25% above AT results in an increase of carbohydrate oxidation rate due to the anaerobic glycolysis. Increases in fat oxidation at the work load by corresponded AT could be an important training protocol for clinical medicine.