We will: 1) compare performance of healthy volunteers and ambulatory adults with traumatic brain injury (TBI) on a range of motor, neurobehavioral and brain imaging outcomes; and 2) evaluate effects of rapid, reciprocal arm and leg exercise with an elliptical trainer on high-level motor coordination and balance, and neurobehavioral and cognitive functioning in persons with TBI. Brain connectivity and changes in connectivity in response to intervention will be quantified. We hypothesize even highly functional adults with TBI will have poorer scores on all measures than controls; exercise will lead to significant improvements in motor performance and balance,and neurobehavioral and cognitive functioncompared to an equivalent length of time during which they were not participating in training . We further hypothesize that improvements in cortical connectivity and representation will relate directly to functional ones.