A RER value closer to 1 indicates which energy source is primarily being used?

A respiratory exchange ratio (RER) value that approaches 1 indicates that carbohydrates are primarily being utilized as the energy source. The RER is calculated by measuring the ratio of carbon dioxide produced to oxygen consumed during metabolism. An RER value of 0.7 typically signifies that fat is the predominant fuel source, while a value closer to 1.0 suggests that carbohydrates are providing the majority of the energy. This is because the complete oxidation of carbohydrates produces a greater amount of carbon dioxide relative to the oxygen consumed compared to fats.

In high-intensity exercise, where energy demands are elevated, the body tends to rely more on carbohydrates for quick energy, resulting in RER values approaching 1. This is especially relevant in activities that require fast bursts of energy, as carbohydrates can be metabolized more rapidly than fats. Thus, an RER value close to 1 is indicative of a predominance of carbohydrate metabolism.