Candidate - The candidate, Christopher Bell, Ph.D., is a physiologist currently supported by an individual postdoctoral fellowship from the American Heart Association. Dr. Bell's past and current research focus has been on the effect of physiological aging on resting and exercise energy expenditure. His immediate goal is to acquire new research and professional skills to help him achieve his long-term goal of developing a successful independent extramurally-funded research program in aging. The proposed K01 development plan should provide Dr. Bell with the necessary training to achieve his goal. Career Development Plan - Dr. Bell's proposed research career development activities consist of: 1) acquiring new research skills associated with and complementary to the proposed research plan; and 2) structured activities including formal course work; attendance and presentation at journal clubs, seminar series, and scientific meetings; and regular interactions with his mentoring team. The overall plan is based on a """"""""translational research"""""""" training model. Environment - The environment for Dr. Bell's research training should be outstanding. The sponsor, Dr. Douglas Seals, is a well-established extramurally-funded scientist with a strong record of successful mentoring in biomedical aging research. He is complemented by several consulting mentors who will provide guidance in specific areas of the training plan. Other faculty in aging research enhances the local training environment. Research - The general aim of this research is to increase our understanding of the mechanisms responsible for changes in beta-adrenergic receptor sympathetic nervous system (beta-AR SNS) modulation of resting metabolic rate (RMR) and thermogenesis with aging in adult humans. I will determine the influence of energy flux (the level of dietary intake and energy expenditure while in energy balance), increased beta-AR responsiveness, and beta2-AR gene variants on beta-AR SNS support of RMR and thermogenesis in middle-aged and older adult humans.