Inclusion/exclusion criteria for TBI:  Inclusion Criteria:  Participants must:  Be TBI survivors > 6 months post TBI Be able to tolerate upright standing for up to 30 minutes. Have joint range of motion within normal functional limits for walking as determined by study staff. Be between 13-35 years of age. Be able to follow directions and commands. Be able to communicate in English. Have stable blood pressure. Not been diagnosed with any cognitive (thinking) deficits.  Exclusion Criteria:  Weight above 300lbs. Joint contracture or spasticity of any limb that limits normal range of motion during ambulation with assistive devices. Have any medical issue that prevents from supporting his/her weight (e.g. orthopedic injuries, pain, or severe spasticity). Have pre-existing condition that causes exercise intolerance (e.g. documented uncontrolled hypertension, coronary artery disease, irregular heart rate or rhythm, or congestive heart failure). Skin issues that would prevent from wearing a harness. Have been hospitalized for heart attack, heart surgery or acute heart failure within 3 months of enrollment in study. Have uncontrolled seizure disorder. Have uncontrolled spasticity that would interfere with walking. Diagnosed with cognitive (thinking) problems prior to TBI. Have neuromuscular or neurological issues (e.g. spinal cord injury, multiple sclerosis, or Parkinson's disease)  Inclusion/exclusion criteria for Healthy controls:  Inclusion Criteria:  Participants must:  Be able to tolerate upright standing for up to 30 minutes. Have joint range of motion within normal functional limits for ambulation. No history of orthopedic, neuromuscular, cognitive or neurological disorders. Be between 13-35 years of age. Have stable blood pressure; no diagnosis of persistent orthostatic hypotension (blood pressure drop of more than 30 millimeters of Mercury in body weight support system). No diagnosed cognitive deficits.  Exclusion Criteria:  Weight above 300lbs Joint contracture or spasticity of any limb that limits normal range of motion during ambulation with assistive devices. Any medical issue that precludes full weight bearing and ambulation (e.g. orthopedic injuries, pain, severe spasticity). Pressure sore that would negatively affect weight bearing, or harness fit. Pre-existing condition that causes exercise intolerance.(Documented uncontrolled hypertension, coronary artery disease, cardiac arrhythmia, or congestive heart failure) Hospitalization for heart attack, heart surgery or acute heart failure within 3 months of enrollment in study. Uncontrolled seizure disorder. Uncontrolled spasticity that would interfere with walking due to neuromuscular or neurological pathologies (e.g., Parkinson's disease, spinal cord injury, or multiple sclerosis) that will interfere with ambulation, or limit the range of motion of the lower limbs Diagnosed with cognitive deficits.