Fatigue Manipulation The user has complete control over the fatigue, a subjective feeling of tiredness, of oneself and others, whether physical or mental. Physical fatigue is the transient inability of a muscle to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. User can increase, decrease/remove, cause or prevent fatigue, or even make it chronic.