Group- and individual-level coincidence of the ‘Fatmax’ and lactate accumulation in adolescents

Fatmax and lactate increase above baseline (LIAB) were measured in 11 adolescent girls and 8 adolescent boys during incremental cycling. Fatmax was the exercise intensity at the point of maximal fat oxidation rate (MFO). The LIAB was the exercise intensity coincident with a sustained increase in blood (lactate) above an initial baseline. We defined the minimum important difference (MID) between the exercise intensity at Fatmax and LIAB as ±8% of both peak \( {\dot{V}}{\text{O}}_{2} \) and peak heart rate (HR). Systematic bias was examined via the mean difference between parameters and its uncertainty, with inference based on the disposition of the confidence interval to the MID. Individual-level agreement was the proportion of differences between Fatmax and LIAB falling within the MID. MFO was at 35 (6)% peak \( {\dot{V}}{\text{O}}_{2} \) with LIAB at 39 (7)% peak \( {\dot{V}}{\text{O}}_{2}. \) Systematic bias was −3.8% of peak \( {\dot{V}}{\text{O}}_{2} \) and −4.4% of peak HR. The estimated population proportion with between-variable agreement within ±8% was 0.76 for both % peak \( {\dot{V}}{\text{O}}_{2} \) and % peak HR. Within the tolerance limits of the MID, the mean bias is ‘almost certainly not’ important; similarly, there is good agreement between the two parameters at the individual level. We conclude that Fatmax and lactate increase above baseline coincide in adolescents.