If you have experienced a concussion, you may wonder when it is safest to resume exercising. Concussions, a type of head injury also known as mild traumatic brain injury, affect many people in the United States -- 128 people out of every 100,000 each year, according to the February 2009 "

A brain injury can be devastating, not only with regard to physical disabilities and lack of function, but for memory, speech, cognitive thinking and reasoning processes as well.

Blunt head trauma can happen from a blow to the head, and result in serious damage to the brain. According to the National Institutes of Health, the impact can range from a minor bump to severe brain injury. According to braininjury.

The brain stem, which is located underneath the limbic system, plays a vital role in the basic life functions of breathing, heart rate, and blood pressure. Three sections, the midbrain, the pons and the medulla, comprise the brain stem.