In review of the literature, a variety of terms are used to describe various types and causes of brain injury. These include head injury, traumatic brain injury, closed or open head injury, concussion, mild brain injury, and specific brain-based conditions such as brain damage due to lack of oxygen to the brain; stroke; brain infections; and exposure to toxic substances. Since the focus of this paper is on the functional impact of brain injury and assisting the individual with a brain injury to achieve improved health and fitness, the cause or type of injury is of less significance. Acquired brain injury, an inclusive term that will be used for this discussion, can be defined as follows:

Acquired brain injury is a non-degenerative injury to the brain that has occurred since birth. It can be caused by an external physical force or by metabolic derangement. The term 'acquired brain injury' includes traumatic brain injuries-such as open or closed head injuries, or non-traumatic brain injuries such as those caused by strokes and other vascular incidents, tumors, infectious diseases, hypoxia, metabolic disorders (e.g., liver and kidney diseases or diabetic coma), and toxic products taken into the body through inhalation or ingestion.