U.S. Air Force Staff Sgt. Christopher Dennis, 52nd Maintenance Group maintenance management analysis NCO in charge, performs leg lifts during Turbo-Charged Challenge #3 in the Eifel Powerhaus at Spangdahlem Air Base, Germany, Feb. 10, 2015. The third challenge required participants to perform a variety of calisthenics and aerobic exercises. (U.S. Air Force photo by Airman 1st Class Timothy Kim/Released)