Fig 2. Kinetics and parameters from PXT_m, GXT_m, and GXT_h using single test analysis.

The same single mouse and man tests were randomly selected from WT males (n = 7) and healthy men (n = 6) and used for derivation of all parameters. (A) RER (VCO₂/ VO₂) represents fuel substrate utilization during PXT_m, GXT_m, and GXT_h. An RER of .85 (solid horizontal arrow) indicates 50% carbohydrate and 50% fat oxidation. In a single test, the point in which there is an abrupt increase in RER is known as anaerobic threshold (AT, dashed arrow). (B) Carbohydrate (dashed line) and fat (solid line) oxidation was determined from RER values (S6 Table) in the PXT_m, GXT_m, and GXT_h. Dotted vertical arrow indicates the crossover time point in the test where there is a shift from predominant lipid oxidation to predominate carbohydrate oxidation.