We aimed to examine the interchangeability of techniques used to assess maximal oxygen consumption ((V) over dotO(2max)) and maximal aerobic power (MAP) employed to express the maximal fat oxidation point in obese children and adolescents. Rate of fat oxidation were measured in 24 obese subjects (13.0 +/- 2.4 years; Body Mass Index 30.2 +/- 6.3 kg m(-2)) who performed a five 4-min stages submaximal incremental cycling exercise. A second cycling exercise was performed to measure (V) over dotO(2max). Results are those of the 20 children who achieved the criterion of RER (>1.02) to assess the attainment of (V) over dotO(2max). Although correlations between results obtained by different methods were strong, Bland-Altman plots showed little agreement between the maximal fat oxidation point expressed as a percentage of measured (V) over dotO(2max) and as % (V) over dotO(2max) estimated according to ACSM guidelines (underestimation : -5.9%) or using the predictive equations of Wasserman (-13.9%). Despite a mean underestimation of 1.4% several values were out of the limits of agreement when comparing measured MAP and Theoretical MAP. Estimations of (V) over dotO(2max) lead to underestimations of the maximal fat oxidation point.