Functional threshold power is not a valid marker of the maximal metabolic steady state.

Functional Threshold Power (FTP) has been considered a valid alternative to other performance markers that represent the upper boundary of the heavy intensity domain. However, such a claim has not been empirically examined from a physiological perspective.This study examined the blood lactate and VO response when exercising at and 15 W above the FTP (FTP). Thirteen cyclists participated in the study. The VO was recorded continuously throughout FTP and FTP, with blood lactate measured before the test, every 10 minutes and at task failure. Data were subsequently analysed using two-way ANOVA. The time to task failure at FTP and FTP were 33.7 ± 7.6 and 22.0 ± 5.7 minutes (p < 0.001), respectively. The VO was not attained when exercising at FTP (VO: 3.61 ± 0.81 vs FTP 3.33 ± 0.68 L·min, p < 0.001). The VO stabilised during both intensities. However, the end test blood lactate corresponding to FTP and FTP was significantly different (6.7 ± 2.1 mM vs 9.2 ± 2.9 mM; p < 0.05). The VO response corresponding to FTP and FTP suggests that FTP should not be considered a threshold marker between heavy and severe intensity.