Using RER to estimate RQ is only accurate during rest and mild to moderate aerobic exercise without the accumulation of lactate. The loss of accuracy during more intense anaerobic exercise is among others due to factors including the bicarbonate buffer system. The body tries to compensate for the accumulation of lactate and minimize the acidification of the blood by expelling more CO2 through the respiratory system.
RER estimation of RQ is reliable only during rest and light-to-moderate aerobic exercise without lactate presence. During intense anaerobic activities, the reliability decreases due to mechanisms like the bicarbonate buffer system. The body adjusts to mitigate lactate effects and blood acidity by increasing CO2 exhalation.