What is Lactate Threshold?
“Lactate threshold”, also known as maximal lactate steady state (MLSS) or lactate turn point 2 (LT2) is one of the most common terms thrown around in the world of endurance sports - and rightfully so. The power/pace at which lactate production and combustion are at equilibrium correlates very strongly with endurance performance. More simply, the faster an athlete’s threshold pace, the more likely they are to perform well. This point is demonstrated in Endurance Performance: The Basics.
What Determines LT2?
Although it is often thought that training at or around LT2 is the most potent stimulus to increase the pace/power at LT2, this is not necessarily the case. This simple thinking ignores the mechanisms which actually determine LT2, which are the VO2 max and VLa max.
As discussed here, the VO2 max represents the maximum aerobic power of an athlete. A stronger aerobic system allows the athlete to oxidize more fat as well as carbohydrate (and lactate) aerobically. The more lactate an athlete can oxidize (use as fuel), the more lactate the athlete can produce and utilize without experiencing acidosis (and slowing down). A high fat and lactate oxidation rate results in a high pace/power at LT2, assuming the lactate production rate (VLa max) is not too high. This leads to the second mechanism that determines pace/power at LT2.
The VLa max, as discussed here, represents the maximum glycolytic power of an athlete. The higher the VLa max, the more lactate is produced per minute. Knowing that lactate is an important fuel for the aerobic system, it makes sense that the glycolytic system needs to be strong enough to supply the aerobic system with enough fuel to meet the energy demand of exercise. However, we also know that too much glycolytic activity relative the strength of the aerobic system causes acidosis in the muscle. Therefore, when aiming to increase power/pace at LT2, it is necessary to balance the VLa to match the VO2. Too high a VLa max and the athlete’s aerobic system is overloaded with lactate. Too low a VLa max and the athlete’s aerobic system can not function to it’s maximum rate. The interplay between VO2 max and VLa max is what determines the pace/power at LT2. LT2 is a result of the body’s primary energy systems, not a system of its own that can be trained.
How to Test LT2
There are many ways to measure or estimate pace/power at LT2. Here are three easy, reliable methods which I have personally used.
1-Lactate Step Test
As the name implies, a lactate step test involves gradually increasing steps of intensity with lactate measurements taken after each step. Once the athlete has created a lactate curve with two clear inflection points, the test can end and LT2 can be determined.
With the right equipment, knowledge and experience, performing a lactate step test is simple and reliable. However, if you don’t have fairly extensive knowledge about lactate dynamics and experience taking lactate samples, this is best left to an expert.
2- 20’ Test
A more simple way to estimate your power at LT2 is with a 20’ all out time trial. After a thorough warm up, ride all-out for 20 minutes with the goal of having the highest average power possible. Taking 90% of this power is a safe way to estimate power at LT2. The downside of this method is that it gives no information besides your 20’ power and a rough estimate for LT2. To increase the usefulness of the 20’ time trial, it is best to also perform time trials of various lengths to build a power duration curve (which will be covered in a future article here). A complete power duration curve gives clear insights into both the LT2 as well as the metabolic strengths and weaknesses of the athlete.
3-RPE
The simplest way to estimate power/pace at LT2 is with RPE (rating of perceived exertion). An RPE of 7 to 8 typically correlates closely with LT2 and can be used in all scenarios of exercise, with or without technology. It is important to judge your effort within the context of the workout, knowing that power/pace with an RPE of 8 at the beginning of a workout will be different than at the end of a workout. Aim to finish the workout at a 7-8 so you don’t over pace the beginning of the workout. Using more technology early on will help to “calibrate” your RPE to match reality.
How to Increase your LT2
Now that the mechanisms behind LT2 are known, it should be clear as to how you can increase your power/pace at LT2.
First, increasing the VO2max is a priority. Long, easy training under the first lactate turn point (LT1) is the primary way to increase VO2max. The goal should be to achieve consistent volume over time, which requires managing your energy well. This can be done by focusing on burning a high amount of fat and limiting the rate of carbohydrate usage. A second way to increase VO2 max is with high intensity training, which is covered here.
Second, to maximize power/pace at LT2, you must balance your VLa max to “match” your VO2 max. On a high level, increasing VLa max can be done with short, fully recovered and maximal effort sprints. Lowering the VLa max can be done with threshold training or dietary manipulations. Specific methods to increase or decrease your VLa max can be found here.
Summary
To summarize, LT2 occurs when the production and oxidation rates of lactate are equal. These rates are determined by the VO2max and VLa max. Testing the LT2 is simple and can be done either with blood lactate measurements or with field time trials. To increase power/pace at LT2, it is necessary to either increase your VO2max or balance your VLa max.
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