Μaximal Fat Oxidation During Cycle Ergometer Protocols in Obese Adults: A Scoping Review

Maximal fat oxidation (MFO) rate and the intensity at which it occurs (Fatmax) are key indicators of metabolic flexibility, yet their assessment in obese populations poses methodological challenges. This scoping review synthesizes evidence from 23 studies investigating protocols for determining Fatmax and MFO during cycle ergometry. Across studies, obese and sedentary participants followed testing procedures, typically involving lower initial workloads, smaller workload increments, and longer stage durations than those used for fitter individuals. In obese populations, Fatmax generally occurred at 30-50% of VO₂ peak, compared with values exceeding 60% in trained participants. While the reliability of Fatmax was acceptable, greater variability was observed for MFO rate. Fitness level appeared to exert a stronger influence than adiposity on fat oxidation, with obesity often associated with a left-shifted fat oxidation curve. Additional factors such as gender, developmental stage, insulin resistance, and type 2 diabetes further modulated these responses. Importantly, short-term training interventions, including moderate-intensity exercise, high-intensity interval training, and Fatmax-targeted protocols, consistently enhanced MFO and shifted Fatmax toward higher intensities, with favorable effects on insulin sensitivity and metabolic health. In contrast, nutritional and supplementation studies provided limited evidence of additional benefits. Overall, Fatmax assessment is feasible in obese populations when appropriate methodological adjustments are applied, and exercise interventions can rapidly enhance fat oxidation capacity. Future research should focus on protocol standardization, mechanistic exploration, and long-term interventions to clarify the role of Fatmax in obesity management and its potential clinical applications.