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Performance Testing, Part 3: VLa max

Updated: Nov 28, 2022

Just as VO2 max (aerobic capacity) gives us insight into the maximal energy production of the aerobic system, VLa max, or maximal rate of lactate production, gives us insight into the maximal energy production of the anaerobic system (anaerobic capacity). There are multiple pathways of anaerobic energy production. The fastest of the these pathways is the alactic anaerobic system. This system is of little importance to endurance athletes due to it’s limited total energy supply and lack of trainability. The second pathway is the lactic anaerobic system, otherwise known as glycolysis. As endurance athletes, this is the anaerobic pathway of interest and the one we will focus on here..

As the name implies, glycolysis is the breakdown of glucose, or carbohydrate, for energy. This energy system provides a relatively fast supply of energy, 2-3 times that of the aerobic system. However, there is a twofold cost to this fast energy supply. First, using the glycolytic system at a high rate quickly drains our limited carbohydrate stores (glycogen) because glucose is the sole fuel for glycolysis. Second, when glucose is broken down by glycolysis, pyruvate is formed (which will be discussed further). Pyruvate is then transformed to lactate, which is accompanied by an acidic hydrogen ion. An accumulation of acidity can quickly inhibit glycolytic enzymes, down regulating glycolytic activity (and the speed of the athlete). VLa max tells us how strongly this system functions. Now that we have an understanding of what the VLa max is, let’s understand why it is useful to the athlete/coach.

As we just learned, glycolysis produces pyruvate, which quickly turns to lactate. The fate of lactate and the speed of the athlete depend on the strength of the aerobic system. Why? As we know, the aerobic system mainly oxidizes (burns) fat and carbohydrate. The aerobic system can be “fed” by fat stored in the body, of which we all have plenty. It can also be fed by the anaerobic system, as pyruvate is the carbohydrate of choice for the aerobic system. So, we have two possible fuels for our aerobic system, fat and carbohydrate (in our case, pyruvate), the later being produced by the anaerobic system. Seeing as the speed of the athlete is proportional to the total energy supplied by the two energy systems, we can see that the more energy made available, the better. We also know that the aerobic system can not provide the maximum amount of energy possible without the production of lactate by the anaerobic system. Finally, we know that the anaerobic system, if too strong, can actually decrease the total energy supply by shutting itself down with acidity. So, how does the athlete maximize the amount of energy they can make available to their muscles over the race distance? By ensuring that their anaerobic system is proportionally matched to their aerobic system. The Vla must be properly balanced, or fine tuned, according to the VO2 max. Let’s look at a diagram to better understand the relationship of anaerobic and aerobic systems, and why this relationship requires the anaerobic system to be optimally developed.

In this diagram by Dr. Howard Luks, we can see that pyruvate has two possible fates. When the anaerobic system produces pyruvate by breaking down glucose, the pyruvate can be taken back up by the mitochondria and oxidized. This is what we want. However, if the mitochondria (aerobic system) are already “saturated” with fuel (pyruvate) from glycolytic activity, they can not take up more pyruvate to burn. This leads to the extra pyruvate “flooding” the muscle and moving to the bloodstream as lactate. In this situation, there is too much pyruvate being produced for the aerobic system to handle. The engine is flooded. This relationship of “feeder and eater” between the anaerobic system and aerobic system is what gives VLa max its importance for endurance athletes. Too little anaerobic contribution doesn’t feed the aerobic engine with enough fuel. Too much anaerobic contribution floods the aerobic engine with fuel. Let’s look further at the practical implication of VLa max on performance and training.

First, we need to state a given. Endurance performance is dictated by the maximal lactate steady state (MLSS, critical power, LT2, FTP, etc). The athlete with the highest/fastest MLSS will likely win a time trial type race. For the endurance athlete, the goal of training is to have the highest MLSS possible. How do you increase MLSS? The first way too increase MLSS is to increase VO2 max. Using a car analogy, the bigger the engine gets, the more fuel it can burn and the faster the car can go. As covered in part one of the VO2 max blog, bigger is better. The second way to increase MLSS is to balance VLa max to the optimal level. With too high a VLa max, you easily flood the engine with fuel. Therefore, lowering a high VLa max will reduce pyruvate flooding. With too low a VLa max, the fuel is only flowing at a trickle, not feeding the engine fast enough. Therefore, increasing the VLa max allows the engine to receive the amount of fuel it needs to run at full capacity. How can we use this information in practice?

To illustrate the importance of knowing the VLa max, using an example is helpful. In this example, we will use a single athlete and look at his test results over time. In our case, we will look at 3 tests, each separated by 8 weeks of training.

Test 1: The athlete performs a series of cycling tests and finds that his MLSS is 280 watts, VO2 max is 70, and VLa max is .5. The coach believes that the best course of action is to lower the VLa max leading up to a race in 8 weeks because this will increase the athlete’s threshold.

Test 2: 8 weeks pass and the athlete has done a lot of tempo/threshold riding. After a successful race, the athlete tests again to see just exactly why it was that the training worked. His threshold is now 290 watts, VO2 max remained 70, and his VLa max is now .35. What has changed? The VLa max decreased. The coach sees that this style of training (lowering VLa max) increased the athlete’s threshold, so the coach implements another 8 weeks of similar training to increase the threshold even more.

Test 3: The athlete has now done another 8 week block focusing on lowering VLa max. The threshold is now 275, VO2 max is 65, and VLa max is .2. The goal of training was to decrease VLa max, which was accomplished (.5 down to .35 down to .2). Why did the athlete see improved performance at first, then end up with a worse performance overall when he simply did more of the same “good” training? Two possible reasons, one of which is known from testing. First, the VO2 max has been eroded, either from lack of training aimed at increasing VO2 max or from overtraining the mitochondria with a high volume of threshold training. Lowering VO2 max (decreasing the size of the engine) lowers the MLSS. The second reason the MLSS got worse can be implied. The athlete started with a VLa max of .5 and had a MLSS of 270. Lowering the VLa max to .35 increased the MLSS to 290. Then, after lowering the VLa max even further to .2, the MLSS got worse. Now the coach knows that the VLa max should be right around .35 for this athlete to optimally use his VO2 max of 70. This is critical information for the coach and athlete when it comes to ensuring the athlete is racing to their full potential. Too high of a VLa max (.5) and the athlete is producing too much lactate. Too low of a VLa max (.2) and the athlete isn’t producing enough lactate. Just like Goldilocks needs her soup to be just the right, the athlete needs their VLa max to be just right. Just strong enough to fully feed the aerobic system but not so strong that it floods the aerobic system. What else can the VLa max tell us?

Beyond helping the coach ensure a proper “peak” for the athlete on race day, knowing the VLa max is important in workout prescription. Remember, VLa max is a maximum rate just like VO2 max. Knowing at what % of maximum you are working at is required to know how intensely you are impacting a system. That’s why the car speedometer turns red once you start reaching near-max speeds. Because this is hard on the engine! The anaerobic system is no different. When the VLa max is low, it is critical to keep the low capacity in mind. How?

Let’s continue with our example athlete who has a low VLa max. What does this low VLa max mean? The anaerobic capacity is low. Therefore, we can infer that the athlete has effectively started to change his fast twitch fibers to function more like slow twitch oxidative fibers, reducing the quantity of fast-twitch-like fibers. This means lower glycolytic activity and higher aerobic energy production. As a coach, you might want to increase this athlete’s VO2 max so you can increase his threshold even more. What is a way to increase VO2 max? By training at high intensity. Let’s say you want to prescribe the athlete with 5x4 minutes at 90-100% of VO2 max to invoke some adaptions that will lead to increased VO2 max. The athlete has a low Vla max, so working at VO2 max intensity feels fairly hard but not too hard. His “fitness” is good. However, working at VO2 max intensity still requires a relatively large contribution from the anaerobic system, both to produce energy anaerobically and to “feed” lactate to the aerobic system to burn aerobically. By working at VO2 max intensity, a good stimulus for his aerobic system, he is now quite possibly overloading his anaerobic system, which is in a weak state. This overload will not cause major damage on a short term basis. However, if the coach doesn’t understand the impact that this workout has on the athlete’s anaerobic system, the coach can easily drive the athlete into unproductive overtraining.

To conclude, VLa max, just like VO2 max, gives the coach/athlete a critical insight into how the athlete’s fitness is composed. This how is far too often overlooked, yet is necessary to know why an athlete is performing the way they are. In the next post, we will cover the possible protocols for testing VLa max.

For more information on testing, coaching, or consulting, please feel free to email me at or message on Instagram (@robbie_deckard).

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