Although soldiers must be ready to respond to occupational and war theatre demands at a moment's notice, there is an epidemic of overweight and obesity and a need for improved fitness and health in the military. Using a cluster randomized clinical trial we propose to test the effectiveness of a High-Intensity Functional Training (HIFT) exercise intervention to improve the body composition and fitness of active duty military personnel. The effectiveness of the HIFT intervention will be compared to usual Army Physical Readiness Training. Main outcomes will include changes in body composition and traditional fitness measures, a test of combat-preparation, and measures of cardiovascular health risk for both groups.