This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Physical activity assessment tools have become increasingly more important in research. Currently, the most common method for assessing physical activity, especially in large populations, is via questionnaire. Although reasonably well validated, this method is less than ideal as it relies on subject recall and also cannot provide accurate information with regard to the intensity of physical activity. An alternative to physical activity recall as assessed via questionnaire is the use of step counters and accelerometers (i.e., motion sensors) although currently available products have serious shortcomings. For example, step counters count steps during walking or running, but they are not useful for estimating other kinds of activities, for providing temporal information about activity patterns, or for estimating activity energy expenditure. Most of the currently available accelerometers also have one or more limitations. Therefore further research and development is needed to make available an accurate, unobtrusive, and inconspicuous activity monitor that can be used for quantifying physical activity in children and adults. Barron Associates, Inc., in Charlottesville, VA, has developed such a physical activity monitor (PAM). The purpose of the present study is to compare energy expenditure estimates from this PAM with actual energy expenditure and heart rate measured via oxygen consumption with a lightweight, portable metabolic measurement system. This research effort is responsive to an NIH program announcement (PAR-03-009; Improving Diet and Physical Activity Assessment) designed to "support research to improve physical activity measurement through improved instruments, technologies, or statistical/analytic techniques," for use in "general and diverse populations."