This study assessed the relationship between rating of perceived exertion (RPE) and time to exhaustion during arm cranking exercise while exercising at two different constant-load exercise intensities in able-bodied and paraplegic individuals. The second aim of this study was to assess the rate of change in the RPE between the two different constant-load exercise intensities in absolute and relative terms. Ten able-bodied men and ten paraplegic men performed four exercise tests: (1) a ramp exercise test (started at 0 W and increased by 15 W min(-1)), (2) a graded exercise test (GXT) (started at 30 W and increased by 15 W every 2 min); these tests were performed in counterbalanced order, (3) a constant-load exercise test equal to 50% delta [i.e., the difference between the gas exchange threshold and peak power output (Δ)], (4) a constant-load exercise test equal to 70% Δ; these tests were also performed in counterbalanced order. There was a strong linear relationship between the RPE and time to exhaustion (R (2) ≥ 0.88) irrespective of exercise intensity and participants' group. As expected, the rate of change in the RPE was significantly greater during 70% Δ compared to 50% Δ when the RPE was regressed against absolute time regardless of group. However, differences in the rate of change in the RPE were removed when the RPE was regressed against proportion of time, irrespective of group. These findings have important implications for predicting time to exhaustion while exercising at constant-load exercise intensity during arm cranking in able-bodied and paraplegic individuals.