Senior Airman Karissa Lee, 911th Security Forces Squadron personnel specialist, leads the pack of 911th Airlift Wing Airmen on a ruck march at the Pittsburgh International Airport Air Reserve Station, Pennsylvania, May 5, 2019. A ruck march is when Airmen carry a backpack full of weights and walk at a vigorous pace over a predetermined course to build up their physical and mental endurance. (U.S. Air Force photo by Senior Airman Grace Thomson)