Is FTP A Valid Metric to Set Training Zones? Examining the Validity of Functional Threshold Power as an Endurance Performance Marker of MLSS

STUDY SUMMARY

Functional threshold power tests can provide a valid estimate of MLSS in endurance athletes, especially well-trained cyclists.

This study examined whether an athlete’s functional threshold power (FTP), determined by a 20-minute time trial, can accurately predict their maximal lactate steady state (MLSS). MLSS is the highest exercise intensity at which lactate levels in the blood remain stable. Finding MLSS requires multiple invasive blood lactate tests, so FTP could provide a simpler method.

The study tested 15 cyclists, 7 classified as trained and 8 as well-trained, based on a maximal oxygen uptake test. The cyclists did an incremental cycling test to exhaustion, a 20-minute FTP test, and multiple cycling tests at different intensities to determine MLSS. The researchers compared the power outputs and heart rates from the FTP and MLSS tests to assess how well FTP predicted MLSS.

For power output, FTP showed a small average difference of 1.4% from MLSS, with a moderate range of uncertainty of 9.2% in all cyclists. The trained cyclists showed a larger average difference and range of uncertainty than the well-trained cyclists. For heart rate, FTP showed a small average difference of 1.4% from MLSS, with a range of uncertainty of 8.2% and a high correlation in all cyclists.

In conclusion, FTP provided a valid prediction of MLSS in both trained and well-trained cyclists for power output and heart rate. Endurance athletes can use FTP tests as a simple alternative to multiple MLSS tests to guide training intensities. The level of accuracy depends on an athlete’s training status, with well-trained athletes likely achieving closer predictions. While promising, more research is needed to confirm these findings before FTP can definitively replace MLSS testing.

Practical Implications

Here are some key training implications from this study for cyclists:

1. FTP tests can be used to estimate MLSS and guide training intensities. Since MLSS is an important threshold for endurance training, FTP provides a simpler alternative to determine appropriate training zones. Cyclists can use their FTP value to set training zones, e.g. Zone 2 below FTP, Zone 3 between FTP and threshold, etc.
2. FTP may be a more accurate estimate of MLSS for well-trained cyclists. The study found a smaller margin of error and range of uncertainty for the well-trained cyclists. So for highly trained cyclists, FTP could be used with more confidence to target MLSS. For less-trained cyclists, some verification with lactate testing may still be useful.
3. Power output from an FTP test can be used, but heart rate response may provide additional guidance. The study found FTP power output and heart rate both provided a valid estimate of MLSS, with a similar small margin of error. Monitoring heart rate during FTP tests and training can help ensure the appropriate intensity is achieved.
4. FTP tests provide a simpler alternative, but lactate testing still has value. While promising, FTP does not definitively replace MLSS testing. Lactate testing can still provide an exact measurement of this important threshold and account for variability. Periodic lactate testing, even if less frequently, may be useful for some cyclists

Follow The FTP/CP Series

This is part of a series of studies we are presenting on FTP, CP, Dmax and their relationship to MLSS and LT2 (or the anaerobic threshold). LT 2 would also serve as a typical dividing line between hard and severe in some session categories, or the break between Zone 2 and 3 in a three-zone system (our preferred system) and between Zone 4-5 in a 5-zone system. Some of these studies' findings correlate, and some diverge. Follow the entire series to see the varying results.
 

ABSTRACT

Is the Functional Threshold Power Interchangeable With the Maximal Lactate Steady State in Trained Cyclists?

Functional threshold power (FTP), determined as 95% of the average power during a 20-min time trial, is suggested as a practical test for the determination of the maximal lactate steady state (MLSS) in cycling. Therefore, the objective of the present study was to determine the validity of FTP in predicting MLSS. Methods: A total of 15 cyclists, 7 classified as trained and 8 as well trained (mean [SD] maximal oxygen uptake 62.3 [6.4] mL·kg⁻¹·min⁻¹, maximal aerobic power 329 [30] W), performed an incremental test to exhaustion, an FTP test, and several constant-load tests to determine the MLSS. The bias ± 95% limits of agreement (LoA), typical error of the estimate (TEE), and Pearson coefficient of correlation (r) were calculated to assess validity. Results: For the power-output measures, FTP presented a bias ± 95% LoA of 1.4% ± 9.2%, a moderate TEE (4.7%), and nearly perfect correlation (r = .91) with MLSS in all cyclists together. When divided by training level, the bias ± 95% LoA and TEE were higher in the trained group (1.4% ± 11.8% and 6.4%, respectively) than in the well-trained group (1.3% ± 7.4% and 3.0%, respectively). For the heart-rate measurement, FTP presented a bias ± 95% LoA of −1.4% ± 8.2%, TEE of 4.0%, and very large correlation (r = .80) with MLSS. Conclusion: Therefore, trained and well-trained cyclists can use FTP as a noninvasive and practical alternative to estimate MLSS.

International Journal of Sports Physiology and Performance

https://doi.org/10.1123/ijspp.2018-0572

Authors: Fernando Klitzke Barszcz, Artur Ferreira Tramontin, Vitor Pereira Costa

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