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We examined whether ratings of perceived exertion (RPE) observed during an incremental (response) protocol could be used to produce target blood [HLa] of 2.5 mM and 4.0 mM during a 30-min treadmill run at a constant RPE. RPE (15.3, 17.6, 19.1), oxygen uptake (˙VO2) (3.31, 3.96, 4.00 l·min-1), velocity (V) (198, 218, 223 m·min-1), and heart rate (HR) (179, 185, 190 bpm) at blood [HLa] of 2.5 mM and 4.0 mM, and peak were determined for nine subjects (5 males, 4 females) during incremental exercise. Subjects then completed two 30-min runs at the RPE corresponding to blood [HLa] of 2.5 mM (RPE 2.5 mM) and 4.0 mM (RPE 4.0 mM) measured during the incremental protocol. For both 30-min runs.˙VO2 was not different from ˙VO2 corresponding to either 2.5 or 4.0 mM blood [HLa] during the incremental test. During the 30-min run at RPE 2.5 mM: (a) only during minutes 25-30 was the blood [HLa] significantly different than 2.5 mM (3.2 ± 0.6 mM, P < 0.05), (b) for the first 20 min HR was significantly lower than the HR at 2.5 mM during the incremental protocol, and (c) V did not differ from V at 2.5 mM during the incremental protocol. During the 30-min run at RPE 4.0 mM: (a) blood [HLa] was not significantly different from 4.0 mM, (b) HR at every time point was significantly lower than HR 4.0 mM during the incremental protocol, and (c) V was decreased over time by an average of 24.6 m·min-1(P < 0.05). Because RPE from the response protocol was able to produce a blood [HLa] close to the criterion value during each 30-min run, we conclude that RPE is a valid tool for prescribing exercise intensities corresponding to blood [HLa] of 2.5 mM and 4.0 mM.