My work uses epidemiological, clinical, and laboratory approaches to evaluate and describe physical performance, fitness, and physiologic reserve. This work has also helped me determine risk factors for and identify potential biological mechanisms responsible for the impairments that result in, functional loss. Data from epidemiologic and clinical investigations have allowed me to understand the specific physical limitations and fitness deficits experienced by children during cancer therapy and by childhood cancer survivors, to identify those most at risk for developing limitations, and to develop interventions designed to prevent physical disability or restore physical health. My more recent work with computational biology and laboratory investigators has allowed me to begin to document the biological processes potentially responsible for the loss of physiologic reserve (frailty) in childhood cancer survivors.