What Happens to the Blood Oxygen Level When a Human Exercises?

Your muscles require up to 100 times the blood flow during exercise than they need at rest, according to Dr. Michael Joyner, one of the principal investigators at Mayo Clinic’s Center for Translation Sciences and Activities. This increased blood flow helps limit the effect exercise has on blood oxygen levels. When your body tissues need more oxygen than they can get, whether during exercise or at rest, you enter a state of hypoxia.

Blood Oxygen Saturation

A device known as a pulse oximeter measures the saturation of oxygen in your blood. The measurement taken using a pulse oximeter shows an estimation of your blood oxygen levels. Normal blood oxygen levels provide pulse oximeter readings between 95 and 100 percent. If your pulse oximeter reading drops below 90 percent, you have low blood oxygen levels known as hypoxemia 1. Hypoxemia eventually causes your tissues to experience an oxygen deficiency, known as hypoxia 1.

Cardiovascular Response to Exercise

Exercise places your body in a state of increased need for oxygen. To meet these needs your cardiovascular system increases its cardiac output by increasing the amount of blood pumped out of the heart with each heartbeat and by increasing the number of times your heart beats each minute. The two mechanisms that allow more blood to flow out of the heart with each heartbeat include dilation of the arterioles within your skeletal muscles and stronger contractions of the ventricles of your heart. As your heart beats faster, blood flows faster through your lungs and the amount of time oxygen has to enter the blood stream decreases, making it harder for your blood to stay oxygenated. While the oxygen level of your blood stays relatively the same sue to this process, your muscles cannot access all of this oxygen and must begin relying on anaerobic processes to continue functioning if exercise continues.

Maintaining Blood Oxygen Levels

Anaerobic processes used within your muscles decreases the pH level of your blood due to the production of lactic acid. The more lactic acid in your blood, the lower the pH. As the pH drops, chemoreceptors responsible for controlling how fast you breathe become stimulated and your respiratory rate increases. This increased respiratory rate helps keep your blood oxygenated to the required levels.


If continue to exercise to the point that increased cardiac output and increased respirations fail to keep your tissues and blood oxygenated, hypoxemia and hypoxia occur and your performance decreases 1. Stop exercising if you experience extreme shortness of breath, lightheadedness, chest pain, decreased coordination or dizziness. These symptoms indicate a problem with your heart or decreased levels of oxygen reaching your brain.