The heart pumps oxygen-rich blood throughout the body. Because a limited volume of blood circulates, the body must decide how to distribute the available blood. Research indicates that during intense exercise, the respiratory muscles begin to demand a greater proportion of the total blood flow thus limiting the blood available to the other exercising musces of the body. In healthy people, strenuous exercise fatigues the diaphragm, the primary muscle that controls breathing. Jonathan Witt is studying whether daily training sessions to strengthen breathing capacity will improve the diaphragm’s efficiency, reduce the amount of blood required when breathing harder, and improve blood flow to the legs. The findings could help patients with chronic obstructive pulmonary disorder (COPD) and cystic fibrosis, whose breathing muscles are overworked, and those with chronic heart failure, who pump even less blood from the heart. The research could lead to new therapies to improve strength and functional capacity in these patients.