Running is a cardiovascular activity which helps to reduce your body fat percentage. Also ,it helps to strengthen your thigh muscles and improve your endurance. Its a controversy whether running helps in loosing tummy as running will help to reduce body fat percentage and not from specific part except if we contract our abbs and run. So if you want to run and want to reduce your abbs too then you can run, tucking your abbs in but it wont be as much effective as abbs resistance exercises for 20 min.