Exercise & Fainting

Resulting from a reduced supply of blood and oxygen to the brain, fainting is a temporary loss of consciousness that generally lasts less than one minute. Fainting can be caused by a wide variety of factors ranging from serious medical issues to dehydration, low blood sugar or high temperatures. Fainting during exercise generally relates to a disruption in blood circulation.


Causes of Fainting

Fainting is caused by a disruption of blood flow to the brain. Since blood is responsible for carrying oxygen, the brain’s oxygen supply also becomes depleted. Typically, this reduced blood flow is caused by a relatively minor disruption in the circulatory system, such as low blood pressure or low blood volume. Certain medications, including diuretics and those for high blood pressure, can lead to low blood pressure. Additionally, moving from a sitting or reclining position to a standing position can cause a sudden drop in blood pressure, resulting in fainting. Low blood volume, on the other hand, is commonly caused by dehydration due to excessive sweating or insufficient intake of fluids during exercise. To avoid dehydration, the American Council on Exercise recommends drinking 7 to 10 oz. of water every 10 to 20 minutes of exercise, along with an additional 8 oz. of fluid immediately after exercising.

Fainting Concerns

The simple act of fainting is generally not dangerous. Since blood flow to the brain is only temporarily reduced, body and brain functions return to normal once blood flow returns. However, fainting causes you to fall, which can be dangerous. Just imagine losing consciousness while running on a treadmill or while lifting 50 pounds above your head. Although fainting is not always easy to prevent, you should always pay attention to the early warning signs to avoid injury.

Early Signs

Fainting can occur with or without warning, making it somewhat difficult to prevent. If you are prone to fainting without early symptoms, be careful about where and how you exercise. Avoid using an exercise machine that requires you to stand high off the ground, and never exercise alone. Early symptoms of an impending episode of unconsciousness might include sudden nausea or rapid heart rate. You might also feel extremely hot, sweaty, lightheaded, dizzy or weak. If you experience any of these symptoms while exercising, stop immediately and lie down for several minutes. Lying down puts your head at the same level as your heart, which helps to restore proper blood flow to the brain.

Things to Consider

To be safe, consult your physician if you faint or experience frequent episodes of lightheadedness during exercise. Although fainting can often be attributed to a minor cause, it could indicate a serious problem with your heart or cardiovascular system. An abnormal heart rhythm or heart valve disorder impairs the heart’s ability to pump blood, which could reduce blood flow to the brain. Blocked or narrowed arteries leading from the heart or to the brain might also result in frequent fainting episodes. A doctor will run a variety of tests to determine the exact cause of your fainting spells.


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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.