The purpose of the study was to identify and compare validity parameters of different absolute intensity thresholds in METs, using relative intensity classification as criterion measure. Convenience sampling was used to recruit total of 112 adults. The participants carried out an incremental maximal cycle ergometer test and asked to perform nine free-living activities. The oxygen uptake was measured by a VO2000® gas analyser throughout the tests. The intensity thresholds were identified using Receiver Operator Characteristic (ROC) curve analysis, having relative intensity categories as criterion measure. A total of 103 participants attended the two visits. Among 54 men and 49 women, the mean (± SD) ages were 36.1 (± 11.1) and 33.9 (± 10.6) years, respectively. The intensity thresholds identified were 4.9 METs for moderate and 6.8 METs for vigorous physical activity. In conclusion, the physical activity thresholds, generated according to the entire sample, were higher and presented improved specificity when compared to thresholds currently recommended. Moreover, these parameters presented relatively high accuracy, even when applied to specific groups such as sex, age, nutritional status and physical fitness.