Functional Threshold Power in Cyclists: Validity of the Concept and Physiological Responses

Functional threshold power is defined as the highest power output a cyclist can maintain in a quasi-steady state for approximately 60-min (FTP60). In order to improve practicality for regular evaluations, FTP60 could theoretically be determined as 95% of the mean power output in a 20-min time-trial (FTP20). This study tested this assumption and the validity of FTP20 and FTP60 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 FTP20. Power output, heart rate and oxygen uptake representing FTP20, FTP60 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 FTP20, FTP60 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 FTP20 was 50.9 ± 15.7 min. In conclusion, FTP20 and FTP60 should not be used interchangeably on an individual basis and their validity against IAT should be interpreted with caution.