Twenty-six physical performance variables were assessed on 100 professional fire fighters and correlated against timed measures of five sequentially performed fire fighting tasks and against fractionated heart rates collected during performance of the fire fighting tasks via Holter monitoring of the ECG. Canonical correlation analysis revealed that two factors, physical work capacity and resistance to fatigue, accounted for the fractionated time and heart rate data. The first factor, influenced heavily by the average intra-task heart rate (L = 0.94) and by the approximately equal weights for the five simulated tasks (-0.53 less than L less than -0.36), reflected the fact that relatively high muscular strength and endurance, coupled with a near maximal aerobic capacity effort, were required to complete the simulated tasks. The battery of physical performance variables best predicting the first factor (R2 = 0.63) included maximal heart rate, sit-ups, grip strength, age, and submaximal oxygen pulse. The second factor (R2 = 0.39), most heavily loaded by the simulated rescue (L = 0.70) and chopping tasks (L = 0.42), appeared to represent an ability to complete all tasks quickly by exhibiting a resistance to fatigue brought on by the demands of the earlier tasks. The battery of physical performance variables best predicting the second factor included lean body weight, maximal heart rate, final treadmill grade, age, and percent fat. This study demonstrated that physiological factors related to the performance of occupational tasks can be identified and measured.