fire a physical fitness test consisting of a 3 mi (4.8 km) hike with a 45 lb (20.5 kg) pack over level terrain to measure fitness for prolonged arduous work; a score of 45 minutes on the pack test approximates an aerobic fitness score of 45 (ml of oxygen per kg of body weight per min) —synonym work capacity —see step test, work capacity This definition last updated 07/22/2008