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

Abstract

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.