There is a big difference between the exercise to condition muscles and the exercise to maintain an injured brain. Muscle exercise is designed to tear down the tissues so that they rebuild stronger. One does not want to tear down brain tissue as in over-stimulating it.

Mental exercise needs to be stopped before the subject reaches brain fatigue. Slowly, the mental exercise can be increased in duration. If mental fatigue is reached, the person should back off for an extended period.

Rebuilding brain 'endurance' can take a long time. The slow progression of building up the length of time can seem tedious. But, overdoing it can cause a relapse that takes even longer.