0843 Ratings of perceived exertion (RPE) are commonly used to assess exercise intensity during aerobic activity. PURPOSE: To identify the relationships between RPE and several physiological measures (PM). METHODS: Results were examined on data collected from 12 male participants (age = 24 ± 2 years; ht = 181 ± 2 cm; wt = 79.9 ± 3.0 kg; VO2peak = 40.4 ± 2.2 ml.kg−1.min−1). Each individual completed a maximal graded exercise test to volitional exhaustion on a recumbent cycle ergometer (workload increased 50 W every 2 min). The subjects' expired air was collected and analyzed by a Physiodyne Max-1 metabolic cart. Each subject was asked to assess their RPE every 2 min. Upon completion of the exercise test, ventilatory threshold (VT) was identified and used as a stratification variable. Relationships between RPE and heart rate (HR), ventilation (VE), ventilation rate (VR), oxygen consumption (VO), relative oxygen consumption (RVO), and RER were assessed during the warm-up (S1), the stage immediately preceding VT (S2), the stage in which VT was met (S3), and the final stage of exercise (S4). RESULTS: No relationships were seen between RPE and any PM during S1. Significant relationships were seen for HR (S2: r = 0.75, p = 0.003; S3: r = 0.77, p = 0.002), VR (S2: r = 0.53, p = 0.03; S3: r = 0.63, p = 0.01), VE (S2: r = 0.67, p = 0.009; S3: r = 0.71, p = 0.005), VO (S2: r = 0.59, p = 0.023; S3: r = 0.54, p = 0.03), RVO (S2: r = 0.58, p = 0.02; S3: r = 0.65, p = 0.01), and RER (S2: r = 0.72, p = 0.004; r = 0.77, p = 0.002). During S4, a significant correlation was only seen for VR (r = 0.72, p = 0.004). Trends were seen for HR (r = 0.30, p = 0.18) and RVO (r = 0.41, p = 0.09). CONCLUSIONS: The results of this investigation indicate that during a graded exercise test, the various physiological responses related to RPE are more numerous during moderate exercise intensities than at either extremely low or extremely high intensities.