Spc. Michael Gavin, a resident of Fleetwood, Pa., and a combat medic with the 7221st Medical Support Unit, Newark, Del., runs on a treadmill while breathing through a mask connected to a monitor that tracks how well he processes oxygen, Feb. 9, 2014, so clinicians at the Army Wellness Center, Aberdeen Proving Ground, Md., can determine his metabolism. Once the metabolism is determined, using measurements from the soldier at rest and exerting, clinicians can tell him how many calories are needed for him to lose, gain or sustain weight. (U.S. Army photo by Staff Sgt. Neil W. McCabe/Released)