Increased numbers of circulating stem cells and physical activity are both associated with improved health in older persons. This pilot study is the initial step in developing a collaborative, translational research project investigating whether physical activity may in part exert a positive influence on aging via the mobilization of stem cells. The specific aim of this pilot project is to collect preliminary data to explore the relationship between physical activity and stem cell populations found in the blood and to determine the variance in the number of circulating stem cells. We hypothesize that stem cell decrease with age, but that persons who are more physically active will have a higher number of stem cells in the blood. A maximum of 40 persons will be recruited to participate. Persons are eligible to participate if they are age 60 or older, haven't been hospitalized recently, do not have an immunologic or blood disease, do not have an infection, and are not undergoing chemotherapy. Subjects will have 2 visits to the UNMC Clinical Research Center (CRC). The first assessment will include an evaluation of health, physical activity and lifestyle via questionnaires. Height, weight and abdominal girth will be measured, and blood will be drawn for immune and stem cell assessment. Subjects will be given a pedometer and accelerometer to wear daily for 7 days. Subjects will return to the CRC for a second visit at which the pedometer and accelerometer will be returned and blood will be drawn. Stem cell and immune assays will be repeated to evaluate the variability of these measures over time. The correlation between stem cell numbers and physical activity will be analyzed. The data will be used to perform sample size calculations for the development of future studies.