There is substantial evidence that a large number of individuals who experience TBI will demonstrate life-long deficits in cognitive or social functions. An estimated 80-90,000 Americans with TBI suffer life-long impairment of physical, cognitive, and psychosocial skills to the degree that they are unable to return to school or work. Research on rehabilitation for mTBI has been minimal and typically has focused on speech, pain management, dizziness, fatigue, irritability, and sensory disorders. The results of the few studies that have examined long-term cognitive effects of mTBI have offered conflicting results. The current research will investigate the efficacy of an aerobic exercise intervention among individuals with mild traumatic brain injury (mTBI). This project will examine changes in fractional anisotropy (FA) values and cognitive functioning among individuals diagnosed with mTBI in a monitored aerobic exercise regimen, versus a low impact stretching and toning control group.