The Coupling of Internal and External Gas Exchange During Exercise

Abstract Muscular exercise imposes a stress to bodily homeostasis that demands an integrated multiorgan response. Intramuscular bioenergetics are supported by a cascade of physiological and biochemical events to supply oxygen, reducing equivalents and phosphates to the muscle mitochondrion, and clear the products of coupled excitation and contraction. The ability to meet in a steady state the intracellular bioenergetic demands (internal respiration) through coupling to pulmonary gas exchange (external respiration) largely determines the parameters of exercise tolerance. This chapter focuses on the control, limitation, and coupling of intramuscular biogenetics to pulmonary gas exchange. It describes: integrative exercise testing protocols; how and when pulmonary gas exchange can be used to provide a noninvasive window on muscular energetics during exercise; mechanisms controlling intramuscular metabolism including phosphate feedback and parallel activation of adenosine triphosphate supply and demand; and how gas exchange is impacted by aging or chronic heart, lung, or muscle disease.