An individual’s ability to metabolize fat has significant ramifications for maximal exercise performance. There is a relationship between exercise intensity, fat oxidation, and carbohydrate oxidation. For example, as exercise intensity increases, fat oxidation decreases while carbohydrate oxidation increases. This can be understood through metabolic gas analysis, where VO2 and VCO2 are measured. By measuring the ratio between the volume of carbon dioxide produced to the volume of oxygen consumed per unit of time, you can calculate a respiratory exchange ratio (RER), which allows you to estimate the type of fuel used for oxidation.
Since both fats and carbohydrates differ in the amount of oxygen used and carbon dioxide produced during oxidative phosphorylation, you can divide VCO2 by VO2 to calculate RER. Typically, RER values will fall between 0.7 and 1.0, with values closer to 0.7 indicating that more fat is oxidized and values closer to 1.0, indicating that more carbohydrate is oxid…
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