U.S. Air Force Airman 1st Class Jackson Nguyen, 1st Maintenance Squadron low observable aircraft structural maintenance apprentice, performs sled pushes during a physical training session at Langley Air Force Base, Va., Nov. 22, 2011. The 1st MXS PT sessions include test fundamentals and more inventive activities, such as sled pushes and parachute sprints. (U.S. Air Force photo by Airman 1st Class Kayla Newman/Released)