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Exercise and Fitness

Exercise and Carbon Dioxide

01/28/2001

Question:

Do different exercises affect the amount of carbon dioxide produced?

Answer:

The chemical composition of carbohydrates, fats, and proteins dictates that different amounts of oxygen are required for their oxidation. A useful calculation in determining the nutrient being utilized and its caloric equivalent is the respiratory quotient (RQ), which is defined as the ratio of carbon dioxide produced to oxygen consumed during the same period of time. The same measurement made at the lung level is referred to as the respiratory exchange ratio (R). This calculation is useful during exercise as an indicator of the relative utilization of the various nutrients for energy.

At rest, carbohydrates, fats, and protein contribute to energy needs. During light exercise protein`s contribution to energy expenditure is reduced, and carbohydrate and fat contribute equally to energy expenditure. Thereafter, R clearly increases as the intensity of exercise increases, indicating a predominant shift to carbohydrate metabolism. During moderate-intensity exercise, however, R progressively decreases with increasing duration as fat becomes the fuel of choice.

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Response by:

Carolyn   Nickol, RD, MEd Carolyn Nickol, RD, MEd
Director
Fitness Center at CARE\Crawley
University of Cincinnati