Comparison of two exercise testing protocols to assess maximal fat oxidation in obese subjects

Purpose: For their relevance in the physical activity (PA), numerous studies investigated different approaches to evaluate maximal fat oxidation (MFO) during exercise and the exercise intensity inducing MFO. The aim of this study was to investigate the use of a short exercise protocol compared to a larger state-to-stage increments protocol on treadmill in obese subjects. Methods: Thirty-six obese adult subjects were involved in this study. Sixteen male (age= 51.5 ± 10.5 yrs, BMI= 36.7 ± 4.8 kg/m 2 ) and twenty female subjects (age= 42.4 ± 12.4 yrs, BMI= 36.5 ± 4.7 kg/m 2 ) performed two exercise testing protocols. In two separate testing sessions, after the body composition assessment, subjects performed a sub-maximal incremental graded test on treadmill. Depending on testing sessions, the workload was increased every 2- or 3-min, evaluating maximal fat oxidation (MFO) and Fat max zone variables. Results: No significant differences were found in heart rate (HR), VO 2 (oxygen uptake ml/kg) and rate of perceived exertion (RPE) at MFO in the 2-min protocol compared with 3-min protocol (105.9±22.3 vs 105.8±14.4; 14.5±2.4 vs 13.7±3.2; 3.0±1.4 vs 3.0±2.0). Significant differences were found in MFO in the 2-min protocol compared to 3-min protocol (576.3±162.9 vs 506.0±148.1). From the analysis of the Fat max zone, no significant differences were found in the VO 2 and HR in high and low borders. Moreover, a statistically significant difference was found in the fat oxidation in low and high borders. Conclusions: Even if the amount of fat oxidation is stage-time dependent, the exercise intensity at which the MFO and the Fat max zone occur is not influenced by the stage-time of the test protocol. Thus, the two-exercise testing protocols could be considered interchangeable to assess the HR and RPE at MFO and at Fat max zone, as variables commonly used to prescribe PA.