Firefighting tasks may require near maximal levels of cardiorespiratory fitness. Previous research has indicated that body fat percentage (BF%) and aerobic capacity (VO2peak) are related to the performance of firefighting tasks. Since a standard submaximal treadmill test for firefighters is terminated at 85% of maximal heart rate (MHR), key performance information relating to maximal cardiorespiratory effort may not be measured in a submaximal test. The purpose of this study was to examine the relationships between body composition and time spent running at intensities greater that 85% MHR. Height, weight, body mass index (BMI; kg/m2), BF%, MHR (bpm), VO2peak(mL/kg/min), predicted VO2peak(P-VO2peak; mL/kg/min), submaximal treadmill test time (WFIsubTest Time; min), and maximal treadmill test time (WFImaxTest Time; min) were collected in fifteen active-duty firefighters. The results indicated that significant relationships (p< 0.05) existed between BF% and VO2peak, BF% and WFImaxTest Time, BF% and Tdiff, and VO2peakand WFImaxTest Time. P-VO2peakwas not significantly different than VO2peak, and the WFImaxTest Time was significantly longer than the WFIsubTest Time. These results indicate that a submaximal treadmill test may reasonably predict VO2peak, but key information about physiological work at intensities greater than 85% MHR may be missed when using submaximal effort tests.