The aim of this study was to determine the construct validity of ratings of perceived exertion categories from 1 to 6 on the Borg category-ratio scale (CR-10) for defining the intensity of continuous aerobic endurance training. Eighteen young and healthy individuals (gender: 4 women and 14 men, age: 28.9±18.3 years, height: 178.5±20.1 cm, body weight: 81.6±11.8 kg, % body fat: 14.41±4.51) voluntereed to execute six continuous running training sessions lasting 20 minutes at an intensity defined by one of the subjective rating categories from 1 to 6, as well as one maximal incremental exercise test. A univariate analysis of variance for repeated measures and a post-hoc test were conducted to determine the difference in acute responses within each individual training session and between the subjective rating categories from 1 to 6. The results show that the variables of oxygen uptake, heart rate, velocity, and minute ventilation significantly increase from the training programmed at RPE 1 to the training programmed at RPE 5. Lactate concentration significantly increases from the training programmed at RPE 2 to the training at RPE 5, and velocity significantly increases across all six training sessions. The analyzed values of oxygen uptake, heart rate, velocity, and minute ventilation during training at RPE 1 and 2 are below the aerobic threshold, indicating moderate intensity domain throughout the 20-minute sessions. During training at RPE 3 and 4, these values fall between the aerobic and anaerobic thresholds, indicating heavy intensity domain, while during training at RPE 5 and 6, they are above the anaerobic threshold, indicating severe intensity domain. The Borg category-ratio scale for subjective rating of perceived exertion (CR-10) has characteristics that allow participants to exercise at different intensities within each of the subjective rating categories from 1 to 6. Additionally, it can be used to determine the intensity of continuous aerobic endurance training in accordance with the moderate, heavy and severe intensity domains. Keywords: