Final answer:
The diffusing capacity can increase during heavy aerobic exercise due to higher oxygen demands of muscles, resulting in increased efficiency of the cardiovascular and muscular systems to deliver and utilize oxygen.
Step-by-step explanation:
The diffusing capacity can increase up to 3x during heavy aerobic exercise because the body needs to meet the higher oxygen demands of the muscles. During intense physical activity, muscles create an oxygen debt, requiring increased oxygen to restore ATP and creatine phosphate levels, convert lactic acid to pyruvic acid, and, in the liver, to convert lactic acid into glucose or glycogen. The oxygen demand triggers the body to increase breathing rate and heart efficiency, thus enhancing the cardiovascular system's ability to supply oxygen to the muscles.
Moreover, exercise-induced physiological changes contribute to this increase in diffusing capacity. An increased heart size and mass result in stronger and more efficient blood pumping, effectively raising stroke volume and cardiac output. Enhanced tissue perfusion allows for improved oxygen delivery, and combined with an increase in the number of circulating erythrocytes, it significantly heightens the body's aerobic capacity.
Aerobic training also elevates the efficiency of the circulatory system, supports the storage of excess oxygen in myoglobin within the muscles, and benefits from the improved uptake of oxygen by hemoglobin due to the Haldane effect. These adaptations collectively explain the increase in diffusing capacity during heavy aerobic exercise.