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Lab Test: Is the Functional Threshold Power (FTP) a Valid Surrogate of the Lactate Threshold?

Updated: Jan 7, 2020

Purpose: This study aimed to analyze the relationship between the Functional Threshold Power (FTP) and the Lactate Threshold (LT).

Methods: 20 male cyclists performed an incremental test in which the LT was determined. At least 48 h later, they performed a 20-minute time trial and 95% of the mean power output (P20) was defined as FTP. Participants were divided into recreational (Peak Power Output [PPO] < 4.5 W∙kg-1, n=11) or trained cyclists (PPO > 4.5 W∙kg-1, n=9) according to their fitness status.

Results: The FTP (240 ± 35 W) was overall not significantly different (effect size[ES]=0.20, limits of agreement [LoA]=-2.4 ± 11.5%) from the LT (246 ± 24 W), and both markers were strongly correlated (r=0.95, p<0.0001). Accounting for the participants’ fitness status, no significant differences were found between FTP and LT ([ES]=0.22; LoA=2.1 ± 7.8%) in trainer cyclists, but FTP was significantly lower than the LT (p=0.0004, ES=0.81; LoA=-6.5 ± 8.3%) in recreational cyclists. A significant relationship was found between relative PPO and the bias between FTP and the LT markers (r=0.77, p<0.0001).

Conclusions: The FTP is a valid field test-based marker for the assessment of endurance fitness. However, caution should be taken when using the FTP interchangeably with the LT as the bias between markers seems to depend on the athletes’ fitness status. Whereas the FTP provides a good estimate of the LT in trained cyclists, in recreational cyclists FTP may underestimate LT.

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