Inclusion Criteria:  65 years old or older. Body Mass Index of 35 or less. Muscle activities will be recorded for distinct muscles in the legs and fatty tissue could interfere with these measurements. Able to walk without a hand held device Able to walk for 5 minutes at their self-paced speed  Exclusion Criteria:  Any past or present history of neurological disorders, heart or respiratory disease, brain injury, seizures, spinal cord surgery, or strokes. Pregnancy. Unable to follow two part commands; Uncorrected vision or severe visual impairment with visual acuity < 20/70 with best correction; Cognitive impairments defined as modified mini-mental score <84; orthopedic or pain conditions (lower extremity pain, back pain, calf pain); refuse to walk on a treadmill; hospitalized 6 months prior to the study for acute illness or surgery, other than minor surgical procedures; lower extremity orthopedic surgery within 1 year; uncontrolled hypertension (> 190/110 mmHg); diagnosed dementia; dyspnea at rest or during daily leaving activities; use supplemental oxygen, resting heart rate> 100 or <40 beats per minute; fixed or fused hip, knee, or ankle joints; progressive movement disorder such as Multiple Sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS), or Parkinson's disease