Doctors and scientists have recently started to uncover what happens when a person sustains a concussion.

According to Dr. William Heinz, a specialist at Orthopedic Associates of Portland, when a person is hit hard enough to cause the brain to bounce off the skull, the result can be an “energy mismatch in the brain.”

“When you have a concussion there is a problem in the glucose transport system,” said Heinz, noting that glucose is the only fuel that the brain uses. “So you’ve got this area of the brain that has been damaged and is calling for more energy to repair itself and the transport system that is supposed to deliver the glucose shuts down.”

Any kind of activity that makes the brain work harder, therefore, heightens the problem. When a person who has a concussion “tries to do things, like read a book or study or concentrate or even go out and try to run, the mismatch gets worse and makes the symptoms worse.”