 Participants will then complete a series of walking bouts on a treadmill while their physical activity and oxygen uptake are concurrently assessed. The walking bouts start at 0.5 miles per hour and end at 6 miles per hour 0.5 miles per hour increments. Treadmill testing will be terminated when any of the following criteria are attained: upon any natural tendency to reach out to use the hand rails to steady andor support themselves, following completion of the fist bout when their heart rate attains 75 of age-predicted maximum heart rateindicative of having achieved vigorous intensity, participants identify as having a 1420 or greater level of exertion on a Borg Rate of Perceived Exertion Scale, following completion of first bout when the participant naturally selects to run instead of walk, following completion of a bout at 6.0 mph, or before any of the above criteria, as the participant prefers, reflecting their personal tolerance. 