REF-875 · Valenzuela et al., 2018 · International Journal of Sports Physiology and Performance, Vol. · Paper · PubMed
Is the Functional Threshold Power a Valid Surrogate of the Lactate Threshold?
Twenty male cyclists did an incremental test to determine the lactate threshold (LT) and, at least 48 h later, a 20-min time trial; FTP was 95% of the 20-min mean power. Across the group FTP and LT were not significantly different and were strongly correlated.
Split by fitness, FTP matched LT in trained cyclists but was significantly lower than LT in recreational cyclists, and the size of the bias was related to relative peak power output. The authors conclude that FTP is a valid field marker of endurance fitness but should not be used interchangeably with LT without caution, because in recreational cyclists it may underestimate LT.
Participants
n=20 male cyclists (abstract: "A total of 20 male cyclists"):
Recreational: peak power output < 4.5 W·kg-1, n = 11
Trained: peak power output > 4.5 W·kg-1, n = 9
Protocol
Incremental test to determine LT (the LT method is not named in the abstract).
At least 48 h later: 20-min time trial; FTP = 95% of the mean power output.
Agreement assessed by effect size, limits of agreement and correlation.
Key Results
| Group | FTP vs LT | Effect size | Limits of agreement |
|---|---|---|---|
| All (n = 20) | 240 [35] W vs 246 [24] W, not significantly different; r = .95 (P < .0001) | 0.20 | -2.4% [11.5%] |
| Trained | no significant difference | 0.22 | 2.1% [7.8%] |
| Recreational | FTP significantly lower than LT (P = .0004) | 0.81 | -6.5% [8.3%] |
Relative peak power output was significantly related to the FTP-LT bias (r = .77; P < .0001).
Practical Application
In 20 male cyclists, FTP (95% of a 20-min test) matched the lactate threshold on average (240 vs 246 W, r = .95) and in trained riders, but in recreational riders (peak power < 4.5 W/kg) it came out significantly lower than their lactate threshold (limits of agreement -6.5% [8.3%]). To "is my FTP the same as my lactate threshold?": if you are a trained cyclist, roughly yes; if you are a recreational rider, your 20-min FTP probably sits below your lactate threshold, so zones built on it may be set a little low.
The fitter the rider (higher peak power per kg), the smaller the gap between FTP and LT (r = .77).
Even where the group means agree, the limits of agreement show that single riders can differ from their LT by several percent; say which test a threshold came from.
Limitations
n=20 men; subgroups of 11 and 9.
One FTP protocol (95% of a 20-min time trial) and one LT determination, whose method is not named in the abstract.
Agreement with LT is not agreement with MLSS or critical power.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level
test validation study, n=20