The validity of predicting peak oxygen uptake ([Formula: see text]) in sedentary participants from a perceptually regulated exercise test (PRET) is limited to two cycle ergometry studies. We assessed the validity of a treadmill-based PRET. Active (n = 49; 40.7 ± 13.8 years) and sedentary (n = 26; 33.4 ± 13.2 y) participants completed two PRETS (PRET 1 and PRET2), requiring a change in speed or incline corresponding to ratings of perceived exertion (RPE) 9, 11, 13 and 15. Extrapolation of RPE: [Formula: see text] data to RPE 19 and 20 from the RPE 9-13 and 9-15 ranges were used to estimate [Formula: see text], and compared to [Formula: see text] from a graded exercise test (GXT). The [Formula: see text] :heart rate (HR) data (≥RPE 15) from the GXT were also extrapolated to age-predicted maximal HR (HRmax(pred)) to provide further estimation of [Formula: see text]. ANOVA revealed no significant differences between [Formula: see text] predictions from the RPE 9-15 range for PRET 1 and PRET 2 when extrapolated to RPE 19 in both active (54.3 ± 7.4; 52.9 ± 8.1 ml kg(-1) min(-1)) and sedentary participants (34.1 ± 10.2; 34.2 ± 9.6 ml kg(-1) min(-1)) and no difference between the HRmax(pred) method and measured [Formula: see text] from the GXT for active (53.3 ± 10.0; 53.9 ± 7.5 ml kg(-1) min(-1), respectively) and sedentary participants (33.6 ± 8.4, 34.4 ± 7.0 ml kg(-1) min(-1), respectively). A single treadmill-based PRET using RPE 9-15 range extrapolated to RPE 19 is a valid means of predicting [Formula: see text] in young and middle to older-aged individuals of varying activity and fitness levels.