The Lactate Threshold

In “The energy systems” the different energy systems of the human body were explained. In that article the phosphagen, aerobic and anaerobic systems were covered and briefly explained. Everybody knows that acidification and lactate production due to the anaerobic system are not desirable during your exercise workout. So it won’t be a surprise that the Lactate Threshold (LT) is such an important parameter in your training plan! 

As discussed previously (The energy systems), the anaerobic contribution to energy production isn’t necessarily problematic. The body is capable of dealing with some of the waste products, as long as it’s produced at a certain rate.  The waste-product production will be more problematic when the production rate surpasses the processing rate of the waste products.

At first there are some buffer mechanisms that may prevent acidification. However, at a certain point, these breakdown and buffering mechanisms won’t suffice anymore. 

At this point, lactate and hydrogen ions will build-up in the blood and within the muscles, resulting in the rise of blood-concentrations, a restricted muscle contraction and deteriorating performance. This tipping point is called a Lactate Threshold. When the contribution of the anaerobic system increases during more intense exercises or bursts, this point will be reached quickly.


A (?) Lactate Threshold

However, as you probably noticed, I called it “a” Lactate Threshold instead of ‘the’ Lactate Threshold. A lot of controversy exists about the exact point  that is called the Lactate Threshold. Probably you can’t even call it one point at all.

Lactate Threshold is a threshold that goes by a lot of terms and definitions. In addition, there are some other terms that may be related to the LT but are defined slightly different. What’s the difference between them?

First of all, there seems to be a difference between two different points:

  • The point that blood lactate starts to rise. 
  • The point that blood lactate starts to rise exponentially and acidification occurs. 



Earlier we used the second definition to describe the Lactate Threshold. Nontheless, some may use the first definition as the Lactate Threshold. This of course will lead to some confusion. For simplicity, as of now, we will use Lactate Threshold 1 (LT1) for the first definition and Lactate Threshold 2 (LT2) for the second definition. 

However, the confusion doesn’t stop here. There are a lot of other variables that are related to the Lactate Threshold(s). No matter what others might say: officially, the Lactate Threshold(s) can only be determined by measuring lactate levels. Yet, there are some other measurements that try to estimate the lactate threshold(s):

  • The (Ventilatory) Anaerobic Threshold (VAT) is the Anaerobic Threshold determined with gas-exchange analysis. By measuring the oxygen uptake and carbon dioxide release during an exercise test, one is able to determine the “First Lactate Threshold (LT1)” pretty accurately. When the Lactate Threshold is determined this way, it’s called the Ventilatory Anaerobic Threshold, or VAT.
    The “second Lactate Threshold (LT2)” may be seen in, and determined with the results of such measurements as well. This is called the Respiratory Compensation Point (RCP).  
    These terms may result in some confusion as some people refer to the VAT (Ventilatory ANaerobic Threshold) as the ‘aerobic threshold‘ and the RCP as the ‘anaerobic threshold‘. Other terms that are often used are the first and second ventilatory thresholds (VT1 & VT2). For simplicity, we use VAT and RCP.

  • The Functional Threshold Power is “the highest power output one can maintain in a quasi-steady state without fatiguing” and is determined as the power output a fit athlete can sustain over approximately one hour. This point coincidences with (but isn’t necessarily exactly the same as) the LT2 or Respiratory Compensation Point. Therefore, the FTP is very practical to determine your training zones. In addition, the same thing can be done when using heart rate, instead of power, as a zone-limiter (FTHR).

  • OBLA (Onset of Blood Lactate Accumulation) is often defined as a blood lactate level of 4 mmol/L. From this point on, it is hard to exercise without reducing the intensity. For a clear and extending description, I would like to refer you to https://www.trackcyclingacademy.com/blog/understanding-lactate-for-track-cyclists. OBLA is near LT2 and RCP (but not necessarily exactly the same), and also, can only be measured directly using lactate measurements!



What does it say about your fitness?

Whereas the cardiovascular fitness sets the upper limit for the aerobic system (reflected by VO2max), it’s the metabolic fitness (reflected by the lactate threshold(s)) that determines the fraction or percentage of VO2max that can be utilized for a certain amount of time without lactate build-up and/or acidification. A higher LT (as percentage of VO2max) has two advantages:

  • An athlete is able to sustain an effort at a certain intensity for a prolonged period.
  • An athlete is able to sustain an effort for a certain duration at a higher intensity.

The faster your body can process waste products, the higher your (second) Lactate Threshold and the faster you will recover from hard efforts. This makes the LT2 the “single most important physiological determinant of performance in events ranging from as short as a 3km pursuit to as long as a 3-week stage race”, according to Dr. Coggan PhD, a well-respected exercise physiologist. LT2 is an important predictor of the endurance performance ability of a cyclist, or for any endurance athlete whatsoever, and therefore provides a strong physiological basis for your training program.


Next: VO2max


Want to know your own VO2max or Lactate Threshold? Or do you need help with your training? Let us know via cycling@science2move.nl or have a look at https://de-vitaliteitspraktijk.nl/inspanningstesten/conditietest/.


References:

  • Friel J. The Cyclist’s Training Bible. 5 ed: VeloPress; 2018.
  • Allen H, Coggan A, McGRagor S. Training + Racing With a Power Meter. 3 ed. Boulder, Colorado: VeloPress; 2019.