Functional threshold power is defined as the highest power output a cyclist can maintain in a quasi-steady state for approximately 60 min (FTP ). In order to improve practicality for regular evaluations, FTP could theoretically be determined as 95% of the mean power output in a 20-min time trial (FTP ). This study tested this assumption and the validity of FTP and FTP against the individual anaerobic threshold (IAT). Twenty-three trained male cyclists performed an incremental test to exhaustion, 20- and 60-min time trials, and a time to exhaustion at FTP . Power output, heart rate and oxygen uptake representing FTP , FTP and IAT were not different (p>0.05), and large to very large correlations were found (r=0.61 to 0.88). Bland-Altman plots between FTP , FTP and IAT showed small bias (-1 to -5 W), but large limits of agreement (-40 to 32 W to -62 to 60 W). Time to exhaustion at FTP was 50.9±15.7 min. In conclusion, FTP and FTP should not be used interchangeably on an individual basis and their validity against IAT should be interpreted with caution.