Lactate threshold concepts in endurance sports: FTP, MLSS, LT, CP, W' explained

Christian Dörr’s doctoral dissertation on the topic “Investigation of the Validity of Various Lactate Threshold Concepts in Endurance Athletes” from the Justus Liebig University in Gießen provides an excellent summary of the subject. Figure 1 gives a great overview of the different lactate-based threshold concepts and the respective definitions of the lactate threshold.

Figure 1: General overview of lactate-based threshold concepts and their respective definitions of the lactate threshold.

As you can see, there are numerous different threshold concepts. The key takeaway is that there is not just one single threshold — rather, it always depends on the specific definition being used in a given study.

For you, it is essential that whenever you undergo a performance test, you always use the same threshold concept. Only then will you obtain values that are comparable over time.

What is FTP?

Functional Threshold Power (FTP) refers to the maximum power output that a cyclist or runner can sustain for approximately one hour. It is considered the gold standard for training control and analysis. FTP gained popularity through watt-based training, which was significantly influenced by the book Training and Racing with a Power Meter by Allen and Coggan.

To determine FTP, athletes often perform a 20-minute power test, where the average power is multiplied by 0.95. This method provides a practical alternative to extensive laboratory tests, allowing athletes to determine their individual performance threshold simply and efficiently.

To learn how performance thresholds can also be measured through heart rate and running pace, check out the blog post “Performance Tests and Performance Data.”

Why is FTP so Important?

FTP serves not only as a benchmark for personal performance but also as the foundation for defining training zones. These zones help athletes structure their training sessions effectively, whether the goal is to improve aerobic endurance or maximize peak performance.

Scientific studies show that FTP strongly correlates with other threshold concepts, such as Critical Power (CP) or Maximal Lactate Steady-State (MLSS). This makes FTP a reliable reference value, useful for both beginners and experienced athletes alike.

Fig. 1: Correlation between CP and FTP (Karsten et al., 2020)

Fig. 2: Correlation between MLSS and FTP (Borszcz et al., 2019)

What Does Science Say About FTP?

Extensive research has examined the validity of FTP. Studies indicate that it generally falls slightly below Critical Power and that both measures often overestimate MLSS. Nevertheless, FTP remains a valuable tool — especially for ambitious amateur athletes — because it is easy to conduct and provides consistent results.

Interestingly, the agreement between FTP and MLSS is particularly high in well-trained athletes. This means that in many cases, FTP provides a valid estimate of an athlete’s actual sustainable power output. However, individual differences — such as fitness level and physiological composition—must always be taken into account.

Limitations of FTP

Despite its advantages, FTP has its limitations. It does not provide detailed insights into the physiological mechanisms behind performance, such as oxygen uptake (VO2max) or lactate metabolism. Additionally, for untrained athletes or those with significantly different physical conditions, FTP may be less precise.

In elite sports, FTP alone is often insufficient for designing complex training plans. Additional diagnostics, such as spirometry or lactate measurements, are necessary to gain a more comprehensive understanding of an athlete’s performance capabilities.

Conclusion: A Versatile Tool with Potential

FTP is an effective, practical tool that allows athletes to base their training plans on solid data. It strikes a good balance between simplicity and accuracy, making it an indispensable tool, particularly for ambitious amateur athletes.

For more precise results and a deeper analysis of individual performance, FTP can be supplemented with additional tests. However, one thing is certain: when used correctly, FTP can be a key to improved training and enhanced performance — an essential companion for anyone striving to reach their full potential.