Objective: Maximal lactate steady-state (MLSS) is a valid and reliable method for determining the lower limit of the severe exercise domain. Meanwhile, a recently introduced technique, called as the highest intensity (I HIGH), has become popular for detecting the upper boundary of severe exercise domain. However, no study has been conducted to question MLSS based on the theoretical basis of this new technique. The aim of this study was to investigate at what level the exercise intensity obtained as a result of applying this method (i.e., IHIGH) to the lower boundary corresponds to the MLSS. Material and Methods: This study was conducted with well-trained 10 cyclists. Fol- lowing exhaustive incremental exercises, participants were subjected to a series of constant work-rate exhaustive exercises to determine their individual work-rates corresponding to the I HIGH. Their individual IHIGH levels were considered as the highest exercise intensity which is still giving peak oxygen consumption ⩒O2peak). The MLSS was deter- mined as considering the highest exercise intensity at which the 30 th and 10th minute blood lactate differences, obtained from 30-minute of submaximal exercises performed at different exercise intensities, could be less than 1 mmol·L-1. Differences between variables were evaluated with paired samples t-test. The effect size (ES) was analysed based on Cohen’s d. Results: As expected, mean ⩒O2 difference between MLSS and IHIGH was significantly different (55.2±4.50 vs. 61.2±5.06 mL∙min-1∙kg-1; p=0.000; ES=2.17). However, when the MLSS was exceeded 5%, exercising ⩒O2 response could not elicit the ⩒O2peak obtained by the method used to determine the I HIGH (60.6±5.02 vs. 56.3±3.42 mL min-1kg-1; p=0.002; ES=1.50). Conclusion: According to the findings, it was revealed that the procedure used to determine a IHIGH for the upper bound and predicted ⩒O2peak for the severe ex- ercise domain are not valid when compared to the lower boundary of the same exercise domain (i.e., MLSS).