Design: Healthy controls with have a single assessment that includes motor, neuropsychological and brain imaging tests. Participants with TBI will have 3 visits with the same motor, neuropsychological and brain imaging tests as the healthy controls. They will perform 2 months of fast elliptical training. . Assessments will occur at 0, 2, and 4 months. The exercise device will be an elliptical trainer that exercises the legs and arms with the emphasis on maintaining a fast speed. Mild resistance will be provided initially and progressively increased once speed is optimized. . The training will be performed in the home 5 days per week for 30 minutes.