How to Fine Tune your VLa max

What is VLa max?

Just as the VO2max gives insight into the maximal rate of aerobic energy production (learn more here), the VLa max gives insight into the maximal rate of energy production by the anaerobic system (glycolytic system). The term “VLa max” stands for maximal rate/acceleration of lactate production. Just as VO2max is given in mL of oxygen consumed per minute per kg, VLa max is expressed as mmol of lactate produced per L per second. This means that a higher VLa max value equals more lactate production per second, meaning faster anaerobic energy production.

What determines VLa max?

Just as VO2max has several determinants, VLa max also has several influencing factors. First, muscle fiber type plays a large role in determining how strong an athlete’s anaerobic system is. The more fast twitch/white fibers* an athlete has, the greater their ability to produce lactate. This is because fast twitch fibers have a higher concentration of glycolytic enzymes that are able to quickly turn glucose into released energy, lactate and hydrogen ions**.

Second, diet can have a large impact on VLa max. Seeing as glucose is the sole fuel for glycolysis, a diet that is chronically high in glucose will prompt the body to rely more heavily on glycolysis to meet energy demand across all intensities. Conversely, a diet low in carbohydrate/glucose will force the body to shift its primary fuel source to what is readily available, mainly fats. Prioritizing different macronutrients (carbs or fat) depending on your current training situation and energy availability is a powerful way to either up-regulate or down-regulate your glycolytic system.

Finally, training strongly affects VLa max. Training that greatly stimulates fast twitch fibers/glycolysis will likely result in an increase in VLa max over time. Conversely, training that activates fast twitch fibers to a moderate level for extensive periods (requiring them to function more like a slow twitch fiber) will down-regulate the glycolytic capacity of those fibers. We’ll cover specific exercises to either increase or decrease VLa max in the upcoming sections.

How to Test VLa max

Unlike VO2max, there is no direct measure of VLa max. This is because it is not possible to measure real-time lactate production inside the muscle fiber while maximally exercising (a muscle biopsy would be required). However, there are several ways to calculate or estimate the strength of your glycolytic system.

The most accurate yet most difficult way to calculate your VLa max is with blood lactate samples. By taking a resting lactate sample, performing an all out sprint, then measuring the max blood lactate achieved, you can calculate the rate of lactate production.

The most common way to estimate VLa max is with software like that provided by Inscyd. These companies have taken hundreds of lab grade VLa max measurements and matched them with power profiles. By performing field power tests and uploading your file to the software, you can have your VLa max estimated very accurately.

Finally, the easiest way to estimate the strength of your glycolytic system is with a simple all out time trial/sprint. This method doesn’t quantify the strength of the anaerobic system like the lactate or inscyd methods. However, you can easily compare your max 20-30” power over time to get a fair assessment of your anaerobic power. However, the anaerobic system is not isolated in this test and therefore the results should be considered within a larger context of a power-duration curve, which will be covered in an upcoming post.

What is an Ideal VLa max?

First, it is important to know the demands of your event and what your current ability is. Identifying your own strengths and - more importantly - weaknesses, is called performing a gap analysis. In regard to VLa max, different events will have different ideal VLa max values.

For long endurance events such as Ironman, marathon or cycling stage racing, a low Vla max is required to maximize performance. Ideally, athletes competing in these events will have a VLa max between .2 to .4 mmol/l/s. On the shorter end of the spectrum (like the 100m in track or swimming), a higher VLa max is required. Values around 1.0 mmol/l/s are ideal. For events around the 3-5 hour mark, a VLa max between .3 and .5 mmol/l/s is ideal.

These values are not arbitrary. Producing lactate at a rate of 1.0 mmol/l/s will drain the energy tank (glycogen) very quickly and will cause far too much acidity in the muscle to function for very long at all. On the flip side, not burning carbs fast enough will leave you feeling flat and slow in shorter events. Balancing your VLa max for your own particular event is what leads to maximal performance.

How to Use VLa max in your Training

Now that you know what VLa max is, what determines it, how to test it, and what an ideal value is, how can you train to optimize your VLa max? Easy!

Training such as weight lifting, explosive movements or sprinting will have an enhancing effect on the VLa max. Why? All of these exercises rely primarily on fast twitch glycolytic fibers. By maximally activating these fibers, you send a signal to the body that it needs more of these fibers to meet the demands of training. Over time, the body will become better at burning carbohydrates quickly.

On the other side, “tempo” or “threshold” intervals are effective at lowering the VLa max. Why? Training at an intensity that activates fast twitch fibers over a long duration forces the fibers to work in a more aerobic, efficient way. Repeating this type of training over time will signal to the body that it needs to become more efficient to meet the demands of training. Increasing the torque applied to the muscle fibers during these efforts places even a larger stress on the fast twitch fibers***.

Finally, bringing your glycogen stores to a low level signals to the body that it needs to become more efficient by burning glycogen at a slower rate, thus better preserving its preferred fuel source.

Summary

To summarize, VLa max stands for the maximal rate of lactate production and is impacted mostly by muscle fiber type. A low VLa max is required for long distance events while a high VLa max is required for short events. Using training and diet to balance the VLa max is critical to maximize performance. Training or diet that increases the percentage of fast twitch fibers will increase VLa max while training or diet that enhances the aerobic qualities of fast twitch fibers will decrease VLa max.

*Fast twitch fibers are often termed “white fibers” because of their physical appearance relative to slow twitch fibers, which are termed “red fibers.” Fast twitch fibers are less red because they contain less myoglobin than slow twitch fibers.

**A common misconception is that lactate, a byproduct of glycolysis, causes fatigue. Actually, lactate is the preferred fuel source of the aerobic metabolism and is not a harmful byproduct. However, the hydrogen ions that accompany lactate are indeed harmful to the muscle cell and cause acidosis if not buffered. The increased acidity in and around the muscle fibers is what causes the classic “burning” feeling when exercise intensity increases.

***The primary determinant of muscle fiber recruitment is torque, not power. If power remains the same, higher torque will recruit more fast twitch fibers while a lower torque will recruit more fast twitch fibers. This is why it’s important to select your cycling cadence based off the goal of the session.