Cadence and Intensity Across the Adult Lifespan

Eligibility Details: Inclusion Criteria: - Adults between ages 21-85 years, able to ambulate on a treadmill (self-report) Exclusion Criteria: - BMI less than 18.5 or more than 40kg/m^2 - Having smoked tobacco within the past 6 months - wheelchair bound, or conditions that prevent normal ambulation - Resting systolic blood pressure > 159 mm HG, or diastolic blood pressure > 99 mm HG - Hospitalization for mental illness within the past 5 years (for the 41-60 and 61-85 year old cohorts this was change to "within the past 1 year"). - Any condition/medication that may affect heart rate response to exercise testing. - Previous history of, or clinical symptoms or signs of, cardiovascular disease, stroke or transient ischemic attacks, chest pain, unusual dyspnea during physical activity/exercise, severe ankle swelling, or leg pain while walking. - Any significant medical condition that may interfere with the study. - Previous history of musculoskeletal injuries or problems causing severe pain during physical activity or exercise which interferes with daily activities. - Participant has a pacemaker or other implanted medical device (including metal joint replacements). - Participant is pregnant. - Participant is unable to complete all testing (1 or two sessions, based on risk factors) within a maximal two week period. - Individuals wearing a full beard may need to be excluded from the study, as large amounts of facial hair around the mouth and nose interfere with the seal of the device that measures the air you breath. Because of this we are seeking participants that are clean-shaven or with a beard where areas around the nose and mouth are clean-shaven (e.g. goatee).