Grey Zone: A Gap between Heavy and Severe Exercise Domain

The aim of this study was to determine a critical threshold (CT) interpreted as “the highest exercise intensity where V̇O2 can be stabilized before reaching 95% of V̇O2max (V̇O2peak)” and compare it with commonly used anaerobic threshold indices. Ten well-trained male cyclists volunteered for this study. Ventilatory threshold (VT) was determined from incremental tests. Multisession constant-load trials were performed to reveal V̇O2max. Mathematically modeled critical power (CP) was estimated through the best individual fit parameter method. Maximal lactate steady state (MLSS) was detected by 30-minute constant-load exercises. The individual CT load of each cyclist was tested by constant-load exercises to exhaustion with +15 W intervals until minimal power output to elicit V̇O2peak. The results showed that work rate corresponding to CT (329.5 6 41.5 W) was significantly greater than that of the MLSS (269.5 ± 38.5 W; p = 0.000), VT (279.6 ± 33 W; p = 0.000), and CP (306.3 ± 39.4 W; p = 0.000), and CP overestimated both VT and MLSS (p = 0.000). There was no significant V̇O2 difference between the 10th and 30th minute of MLSS and MLSS + 15 W exercise (0.36–0.13 ml·min-1·kg-1; p = 0.621). Exercising V̇O2 response of MLSS + 15 W could not exceed the level of 95% V̇O2max (57.02 ± 3.87 ml·min-1·kg-1 and 87.2 ± 3.1% of V̇O2max; p = 0.000), whereas V̇O2 responses greater than 95% of V̇O2max were always attained during exercises performed at CT + 15 W (64.52 ± 4.37 ml·min-1·kg-1 and 98.6 6 1% of V̇O2max; p > 0.05). In conclusion, this study indicates that there is a “grey zone” between heavy and severe exercise domain. This information may play a key role in enhancing athletic performance by improving the quality of training programs.