My research seeks to understand the interplay among stress, aging, and exercise. It is unquestionable that habitual physical activity promotes health. My recent randomized controlled trial is the first to demonstrate that 6 months of exercise can reverse cellular aging of the immune system in previously inactive, highly stressed adults. These results invite a compelling question: does exercise benefit the immune system simply by bolstering basic cell mechanisms associated with aging or additionally by bolstering adaptive psychological and biological stress processes that can directly improve immune function? I am currently developing new intervention trials and laboratory based studies to disentangle the extent to which both acute and long-term exercise can strengthen both psychological and biological stress responses and immune function in children and adults alike.