Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of pancreatic β cells and culminating with absolute insulin deficiency. Intensive insulin therapy is the standard of care for individuals with T1D, but attaining optimal glycemic control is extremely onerous and requires multiple daily insulin injections or continuous subcutaneous insulin infusion by an insulin pump, complemented by frequent monitoring of blood glucose (BG). Besides the usual barriers (i.e. lack of time/space, low energy, work etc.) individuals with T1D list fear of hypoglycemia as an important barrier to engage in PA. During PA there is an increased risk of hypoglycemia and pronounced glycemic imbalance. Moreover, exercise me- diated hypoglycemic risk is amplified not only during the bout of exercise but also for many hours after. The objective of this dissertation is to both understand the glycemic challenges associated with physical activity and develop model-based decision support systems to assist these individuals during and after PA.