Basics of Metabolism
Metabolism can be defined as the sum total of processes occurring in a living organism. Because heat is produced by those processes, the metabolic rate is indicated by the rate of heat production. All processes of metabolism ultimately depend on biological oxidation, so measuring the rate of O2 consumption yields a good estimate of the rate of heat production, or metabolic rate. The maximum capability of an individual to consume oxygen (V O2 max) is highly related to that individual’s ability to perform hard work over prolonged periods. A high capacity to consume and utilize O2 indicates a high metabolic capacity.
Metabolism can be estimated in two ways: by direct determinations of heat production and by determinations of °2 consumption. Determinations of metabolic rate provide valuable information about the status of an individual. In resting individuals, both methods provide similar results. During exercise, direct calorimetry is not feasible; therefore, indirect calorimetry must be used. However, during hard and prolonged exercise, indirect calorimetry may not provide a precise estimate of metabolic rate. Under these conditions, determinations of O2 consumption still provide important information about the cardioventilatory systems.
