Through the past few centuries, the study of muscular exercise has provided us with many facts of how the prospect of exercise can initiate the process of the body to mobilize mechanisms to meet using respiratory and circulatory demands. Exercise not only involves the muscles but also other tissues that it depends, on an extraordinary coordination of the nervous, circulatory, and respiratory systems. In order to ensure a proper supply of oxygen for the working muscle during exercise, the body must coordinate with the interaction of the lungs, the blood, the heart, the circulatory, and the muscle cell itself.
Oxygen enters the bloodstream and carbon dioxide leaves it by way of the alveoli, which are the tiny sacs that form the structure of the lung. The maximal oxygen intake however on a normal person does not have so much to do with the capacity of the lungs for ventilation or diffusion, but with the maximal pumping capacity of the heart.
After ventilation of the lungs, the next adaptation to exercise is hemoglobin. Hemoglobin transports and delivers oxygen in the body. The biological properties of hemoglobin play a very important role in the enabling the body to adapt to exercise. Hemoglobin enables our bodies to allow a flow of only about five liters of blood per minute supplying us with the correct amount of the bodies needed oxygen at rest. Without hemoglobin we would have to depend on dissolving oxygen in a carrier fluid like blood plasma which would require humans to circulate 300 pounds of fluid at rest per minute.
The pumping and circulation of the blood is the next link to adjustment of exercise. At peak demand for oxygen, the heart increases its output by speeding up its rate of beating and by increasing the volume of blood pumped at each stroke. Based on available evidence, it is noted that under moderate stress the heart may increase either it's pulse rate or stroke volume, depending on the persons physical training and exercise history.