Evaluation of a graded exercise test to determine peak fat oxidation in individuals with low cardiorespiratory fitness

The aims of this study were to develop a graded exercise protocol employing four-minute stages to observe whether steady-state gaseous exchange was attained within four-minutes and to assess the graded test’s surrogate validity and day-to-day reliability to determine rates of peak fat oxidation during exercise (PFO) in individuals with low cardiorespiratory fitness. This study was a cross-over design where sixteen healthy adults first completed an incremental graded exercise test (GE) followed by three short continuous exercise (SCE) sessions all in an overnight fasted-state (11 ± 1 h). The GE test was completed to determine rate of peak fat oxidation during exercise (PFO) and FATMAX i.e. the exercise intensity PFO occurred at (measured in absolute watts). The three SCE sessions were completed in a randomised order on separate days and involved completion of the graded test to the stage: 1) preceding (SCEpre); 2) equal to (SCEequal); or 3) after (SCEpost), PFO was attained, where participants then continued to cycle for 10-minutes at that respective intensity. Expired gases were sampled at minutes 3-4, 5-6, 7-8 and 9-10 and substrate oxidation rates were assessed via indirect calorimetry.