What does the Respiratory Exchange Ratio (RER) assess?

The Respiratory Exchange Ratio (RER) specifically assesses the ratio of carbon dioxide expelled from the body to the oxygen consumed during metabolism. This ratio provides critical insight into the predominant energy substrates being utilized by the body—carbohydrates or fats—during different types of physical activity. An RER value closer to 1.0 indicates a higher proportion of carbohydrates being metabolized, while a value closer to 0.7 suggests a predominance of fat metabolism.

Understanding RER is essential for personal trainers and fitness professionals as it helps them tailor training programs based on the energy systems being used during exercise. For example, knowing whether a client is primarily burning fat or carbohydrates can influence the approach to conditioning and nutrition strategies for optimal performance and weight management.