Physical Activity in Transition-Age Youth on the Autism Spectrum - PROJECT SUMMARY/ ABSTRACT The long-term goal of this K23 Career Development Award is to prepare the PI (Yu-Lun Chen, PhD) for an independent research career that aims to promote physical activity (PA) and health in people on the autism spectrum, with a focus on transition-age youth on the spectrum (TAYS). PA, defined as any bodily movement increasing energy expenditure above a basal level, is critical in promoting physical and mental health and preventing adverse health conditions. However, TAYS are four times less likely to achieve the recommended PA levels than typically developing peers. This is a significant health concern for TAYS that not only diminishes their quality of life but also correlates with a nearly doubled risk of obesity compared to the general population. Inactive lifestyles in TAYS likely persist into later adulthood and may increase risks for chronic diseases in later adulthood. For instance, adults on the spectrum face more than doubled risks of type 2 diabetes and cardiovascular diseases compared to the general population, suggesting an urgent need to promote PA in TAYS and avert negative health outcomes. However, high-quality PA interventions for TAYS are scarce due to key knowledge gaps including a lack of validated, objective outcome measures of PA behaviors in TAYS, as well as limited scientific knowledge on the modifiable factors unique to TAYS that are associated with PA and can serve as potential intervention targets. The K23 research will address these through the following aims: 1) to calibrate and validate wrist accelerometer output of PA measures to account for repetitive hand movements in TAYS; 2) quantify patterns of PA behaviors in TAYS in everyday life; and 3) identify modifiable intervention targets for PA by systematically assessing predictors of daily PA behaviors including functional impairment, contextual barriers, and motivation. The proposed K23 research project will generate novel data on PA outcome measures, patterns of PA behaviors, and modifiable targets for intervention for TAYS, enabling the development and evaluation of a high-quality PA intervention in subsequent R21 and R01 proposals. The proposal expands the PI’s prior training in health outcomes research with TAYS to develop an innovative research program in PA promotion, a critical yet understudied topic. The K23 training plan involves PA measurement validation, accelerometry data analysis, and community-engaged PA intervention development. The K23 mentoring team has extensive mentoring experience, multidisciplinary expertise directly relevant to the proposal, and a history of productive collaboration with the PI. By the end of the training, the PI will be able to incorporate wearable accelerometer measures in mobile-health PA research and develop an independent research program on health promotion in TAYS, ultimately improving well-being and preventing chronic health conditions in these vulnerable populations.