Lactate has long been used by exercise physiologists and sports coaches during indoor and outdoor exercise testing to define the so-called ‘lactate thresholds’. Due to the use of different terms and methods for determining these thresholds, there is a lot of confusion and misinterpretation. Typical terms are the aerobic threshold, the anaerobic threshold, lactate threshold 1 (LT1), lactate threshold 2 (LT2), maximal lactate steady state (MLSS),… Here we will try to clarify the lactate thresholds and how to determine them.
Figure from Faude, O., Kindermann, W. & Meyer, T. Lactate Threshold Concepts. Sports Med39, 469–490 (2009). https://doi.org/10.2165/00007256-200939060-00003
Lactate was long believed to be something bad that accumulates in the body when increasing the exercise intensity and causes sore muscles. Now we know that lactate isn’t a waste product but is an essential metabolite that the body can use as fuel during exercise. At low intensities, the lactate produced in the muscles can be used as a fuel in other muscles. Above a certain threshold, the lactate production will be higher than the elimination and starts increasing exponentially. This point is mainly called the lactate threshold or maximal lactate steady state.
Defining the lactate thresholds
The best way to define the lactate thresholds is by an incremental exercise test in a sports science lab. This incremental test will be done on a bicycle ergometer (with your own bike if you are a trained athlete) or running a treadmill and start at a low intensity. This intensity will be increased stepwise until exhaustion. The most common are step lengths of 3 to 5 minutes and increase with 30-50 Watt for cycling or 1-2 km/h for running. To get a stable lactate value during the steps, longer step lengths are better. During this exercise test the heart rate is measured continuously, and the blood lactate values are measured at the end of every step with a small drop of blood. With the IDRO sweat lactate sensor, these measurements can now be done non-invasive and continuously.
At the end of the test, the lactate profile of the athlete can be defined. This profile can be used to evaluate the strengths and weaknesses of an athlete and to define the lactate thresholds. The first lactate threshold is mainly defined as the first rise in the lactate curve. The second lactate threshold is where the exponential increase in lactate starts. The later (with higher power outputs) these thresholds occur, the better trained the athlete is.