When you exercise, many physiological changes take place to make sure your muscles have enough oxygen to do their job. You blood vessels are able to widen and narrow to redirect the flow of oxygenated blood to your exercising muscles. Regular exercise enhances vascular health, but unhealthy vessels can become narrowed or blocked by plaque, impeding blood flow to your heart, and putting you at risk for chest pain or even cardiac arrest.
Muscle and Flow
During exercise, your muscles need oxygen to break down fats and carbohydrates for energy. To make room for fresh oxygen, the muscles release byproducts such as adenosine and carbon dioxide, which prompt the blood vessels in that area to dilate or expand, a process called vasodilation. This vasodilation allows more oxygenated blood to be delivered to the muscles. In a healthy body, vasodilation takes place in the coronary blood vessels that surround your heart, and in your skin and the blood vessels of your muscles.
When you exercise, one way the increased demand for oxygen in your exercising muscles is met is by redirecting blood from the inactive tissues of your body, such as your abdomen and kidneys. Your sympathetic nervous system, part of the brainstem and spinal cord, stimulates the blood vessels in non-active tissue to constrict, or narrow, reducing blood flow to those tissues. The blood flow is then redistributed to your active muscles.
You may wonder how the sympathetic nervous system can only command the blood vessels of nonessential tissues to constrict while leaving your working muscles untouched. The sympathetic response causes a widespread vasoconstriction throughout your whole body. However, the chemical byproducts produced by your working muscles override this response where necessary. A 2004 report published in the "Journal of Physiology" demonstrates that the circulating byproducts play a role in oxygen delivery regulation by inducing vasodilation and blunting the sympathetic vasoconstrictor activity. Regular endurance training enhances your efficiency in regulating blood flow.
In people with conditions such as heart or vascular disease, the blood vessels may not respond appropriately during exercise. For instance, if you have a blockage in one or more of your heart vessels, vasodilation could be impaired, robbing your heart muscle of oxygenated blood and possibly causing symptoms such as chest pain. Similarly, peripheral vascular disease can cause lesions in the blood vessels of your limbs, preventing adequate perfusion, or blood flow. To remedy these conditions, physicians may prescribe medications called vasodilators that will artificially widen your vessels. More invasive surgical procedures also may be an option.
- William D. McArdle: Essentials of Exercise Physiology
- Journal of Clinical Investigation: Endogenous Adenosine Mediates Coronary Vasodilation During Exercise After K(ATP)+ Channel Blockade
- Journal of Applied Physiology: Attenuated Sympathetic Vasoconstriction in Active Skeletal Muscles During Dynamic Exercise
- Journal of Physiology: Circulating ATP-Induced Vasodilatation Overrides Sympathetic Vasoconstrictor Activity in Human Skeletal Muscle