Summary Venous thromboembolism (VTE) is the third most common cardiovascular disease in the United States. Venous stasis, which can occur during prolonged periods of inactivity, is a known risk factor for VTE; however, the relationship between physical activity and VTE is inconsistent and guidance regarding physical activity after a VTE is lacking. The overarching goal of this proposed “Administrative Supplement for Continuity and Retention of NIH Mentored Career Development (K) Award Recipients and Scholars” is to provide supplemental support of the scientific and training aims of the NHLBI-funded K01, “Physical Activity, Sedentary Behavior, and Venous Thromboembolism Risk”, following a life event. Dr. Laura B. Harrington's ongoing parent K01 award aims to further our understanding of physical activity and sedentary behavior in relation to: (1) incident VTE risk, (2) short-term VTE risk following physical activity, (3) long-term prognosis following an incident VTE, and (4) hemostatic factor levels, which are associated with thrombotic event risk. This study leverages existing data from the Women's Health Initiative and the Nurses' Health Studies I and II cohorts in addition to newly collecting data in the setting of a case-crossover study. Innovative aspects of the proposed work include the evaluation of accelerometer-measured physical activity and sedentary behavior in relation to VTE risk, the evaluation of VTE risk following physical activity using case-crossover methodology, the evaluation of physical activity and sedentary behavior with long-term prognosis among VTE survivors, and the evaluation of usual physical activity in relation to hemostatic parameter measures. Not only are the proposed scientific aims of