Lactate Threshold: Definition, Role and Measurement in Athletes

Endruance athlete running on trail
Lactate threshold is a key component in determining endurance performance.

It’s a common misconception that lactate threshold is the point where blood lactate begins to rise above resting levels. That’s too broad a statement.

So, what is it exactly? While the definition will vary between textbooks and who you ask, the following general explanation is commonly accepted.

What’s Lactate Threshold?

Lactate threshold (LT) is a common term used to describe the point of a spiked increase in blood lactate during incremental exercise. Another term that is often used is the ‘onset of blood lactate accumulation’ (OBLA).

Unless we measure lactate directly in the muscle, determining lactate threshold is somewhat confined to the finger stick method using a portable blood lactate analyzer.

Getting a sample of blood and measuring the lactate that’s in it is relatively easy. But, how can blood lactate tell us about what is happening in the muscle?

Blood lactate does not change significantly from rest to moderate intensity, but just like ventilat1on, there’s an exercise intensity at which it begins to increase exponentially; that’s LT.

Why the sudden increase?

First of all, you must understand that during exercise, lactate is produced (for the most part) in working muscle and when a high enough intensity is reached, the rate of lactate production starts to spike (it increases enough that it must spill out of the muscle into the blood).

Some explanations for the rise in blood lactate are the following:

  1. Increased rate of glycolysis and production of NADH and pyruvate.
  2. Increased use of Type II fibers.
  3. Decreased rate of lactate removal from the blood.

Regarding #3, the simple equation below explains how an increase in blood lactate is not just the result of how it’s produced:

Blood lactate = lactate entry into the blood – lactate removal from the blood

Role of LT in Determining Endurance Performance

Simply analyzing blood lactate tells us very little about what is happening in the muscle, however, is still a very meaningful and useful measurement in athletes because it’s relevant to endurance performance. Outside of medical testing for diagnosing tissue damage and certain diseases, it has no real meaning for the person who is not an endurance athlete.

Lactate threshold is highly correlated with endurance performance: the higher the LT relative to VO2, the better the endurance performance.

For instance, LT at 85% of VO2max provides an athlete a greater performance advantage than LT at 70% of VO2max. Take a look at the table below and consider each of the four runners.

 
Runner A
Runner B
Runner C
Runner D
Running pace (mph)
8
10
10.5
11
VO2 (ml/kg/min) at this pace
47
59
62
62
VO2max
67
73
73
73
%VO2max at LT
75
80
85
85

Most of you realize the importance of a high VO2 max with respect to endurance performance. But how exactly does LT affect performance? Greatly, as you can see.

Consider that you have measured VO2max and LT for each of these runners. Now they are racing in a marathon. Who is the fastest runner? Hopefully you said Runner D; after all, her running pace is the greatest and, no matter how you look at it, the fastest runner always wins – period. In contrast, it is obvious that Runner A is not a contender. So, what makes these runners different from one another.

It’s obviously not VO2 max. While VO2 max is critical to endurance athletes, when you compare the bunch of them to each other, there isn’t much difference in VO2max values; rather, other factors will determine performance. And one of the most significant factors is LT as you can see from this example. The later that lactate threshold occurs, the better the performance. An other important factor is running economy or efficiency.

So, if you are trying to train endurance athletes (cyclists, runners, swimmers, etc.), you should make sure to concentrate on strategies for raising LT, such as interval training.

How To Measure Lactate Threshold

What is a typical LT? How do we express it? Would it make sense to you if in the middle of your endurance training session your LT was determined to be 4.5 mmol/L?

Well, if you don’t know how fast you are running when you reach LT, don’t know your heart rate at LT, or know at what percent of your VO2 max it occurs, then it’s basically useless information. The reason being – it’s critical that when LT is determined it is associated with an exercise intensity; quantified by rating of perceived exertion (RPE), heart rate, or as a percentage of VO2 max.

Knowing heart rate at lactate threshold is very useful to an athlete because he or she can easily measure heart rate during a workout or race to know whether they are above or below LT. Typically, the best endurance athletes hit LT above 80% VO2max (some as high as 90%). For comparison, untrained individuals fall within 50 – 60% VO2 max and non-elite athletes fall somewhere between untrained and elite. Lance Armstrong’s LT has been measured at between 90 – 95% of VO2 max on the bike!

Now let’s talk about how to measure it.

To determine LT, a graded exercise test (GXT) is necessary. Typically a test for LT is performed after VO2max has been determined, but you can combine the two and measure lactate during a maximal GXT. Lactate is usually measured in milli-moles per liter of blood or mM/L – it’s basically a way to express the concentration of lactate in your blood.

The following is a quick guide for performing a GXT to determine LT:

  1. The initial intensity should be low, about 40% VO2max.
  2. Incremental increases in load should be small, about 5-8% VO2max or 1 MET. Small increments assure more precise determination of LT.
  3. Length of each stage affects blood lactate levels. Long periods (4-6 min) are used to allow tissue lactate to be well reflected in blood. Shorter periods (continuous increase every 30 seconds) are used to gain sharp changes in lactate and to restrict its removal from blood. A moderate length (1-2 min) is often recommended.
  4. VO2 and heart rate data should be recorded at each stage.
  5. Fingertip blood samples should be taken during the 15-20 second period following each stage. Consistency is key.
  6. If blood is immediately analyzed, LT can be determined before achieving maximal loads. Normally, the test is carried out until voluntary termination.
  7. Peak blood lactate can be determined from maximal loads. Rate of recovery can also be determined by sampling immediately post-exercise and every 2 min for a total of 4 measures.

Once the GXT has been performed and lactate measures have been taken, the lactate response to exercise is graphed. The graph below illustrates one method for determining LT.

Graph plotting blood lactate vs percent VO2max

  1. Measure blood lactate increase between each consecutive data point.
  2. Find where the increase between a set of points is 1mM or greater.
  3. This interval represents lactate threshold and you can determine the heart rate and/or percentage of VO2max it occurs.

Keep in mind that before LT is achieved, lactate values vary little (within 1 mMol/L of each other). But at some point, there is an increase equal to or greater than 1 mM/L and this is the criterion that can be used to establish LT.