Oxygen transport and utilization: an integration of the muscle systems.

Exercise offers a unique stage from which to study and teach the integration of physiological systems. In this article, the process of matching O(2) transport from air to its ultimate consumption in the contracting cell is utilized to integrate the workings of the cardiac, smooth, and skeletal muscle systems. Specifically, the physiology of exercise and the maximal oxygen consumption (V(.)O(2 max)) achieved through the precise linking of these three muscle systems are utilized to highlight the complexity and importance of this integration. Smooth muscle plays a vital "middleman" role in the distribution of blood-borne O(2) to the appropriate area of demand. Cardiac muscle instigates the convective movement of this O(2), whereas skeletal muscle acts as the recipient and ultimate consumer of O(2) in the synthesis of ATP and performance of work. In combination, these muscle systems facilitate the remarkable 15- to 30-fold increase in metabolic rate from rest to maximal effort in endurance-type exercise.