
If VO2max is the size of your engine, think of VLamax as the turbo boost.
So what is VLamax and how does the INSCYD test determine it?
Once you've found your VLamax how should your training be tailored to increase or reduce this performance metric?
To better understand the concept of VLamax it is worth familiarising yourself to the 3 main energy systems in the human body that can deliver energy to your muscles: The ATP-PCr, glycolytic and aerobic systems. In the chart below the relative contribution from each of these systems is shown. A more detailed overview is available here

From this chart you can conclude that for very short exercise bouts (i.e. very high intensity or power), ATP-PCr is contributing the most energy. After that and until about 1 minute the glycolytic system delivers the majority of the energy. After that the aerobic system takes over.
Note that although after about 1 minute the aerobic system is highest, the glycolytic system is contributing significantly to the total energy supply. Lactate is a by product of an active glycolytic system. At lower intensities lactate is still being produced, however the rate of combustion is greater therefore the is no accumulation. ATP-PCr and the Aerobic system do not produce lactate.

Pyruvic acid (or “pyruvate”) plays a role and is a limiter in both the lactate shuttle (the process that clears lactate from you muscle and transforms it into a substrate that can be used for aerobic energy delivery) and fatty acid oxidation. In other words: you need pyruvate to clear lactate and to burn fat.
Pyruvate availability seems to increase linearly with your VO2 (i.e. at lower intensities it is lower than at higher intensities) and pyruvate demand for the lactate shuttle takes precedence over fatty acid oxidation (i.e. if there is pyruvate demand for the lactate shuttle it will be used for that and not for fatty acid oxidation).

The chart above is 2 different riders lactate curves. The red line is the lactate production from their glycolytic system. The blue line is the lactate combustion capacity as made possible by pyruvate availability. As mentioned before, lactate combustion has a linear relationship with your oxygen consumption (VO2), explaining why it levels off at higher intensities (i.e. your VO2max). The point at which the red and blue lines intersect (the point at which lactate production is equal to the lactate combustion capacity) is your max lactate steady state or anaerobic threshold. Intensities above this threshold will result in a significant increase in blood lactate concentration and eventually exhaustion.
The area between the red and blue lines represents the pyruvate capacity that is available for fatty acid oxidation. In the chart below this pyruvate capacity is plotted, showing a maximum at FatMax.

To summarise: VLamax is the maximum rate of lactate production. A high VLamax indicates will mean that even at lower intensities your lactate production might be relatively high. A low VLamax indicates that your lactate production stays low even at higher intensities. This information is very interesting because it can be used, as you have seen above, to determine e.g. interval intensity and recovery, FatMax and anaerobic threshold.

A high VLamax is not good or bad. It is merely a tool to describe your energy metabolism at different intensities. For a sprinter a high VLamax (anaerobic power) is good, at the cost of a lower anaerobic threshold, for a time trialist a low VLamax might be good, at the cost of a lower maximum anaerobic power. Understanding how to train to increase or decrease VLamax is crucial for every aspect of sport, from sprinting to endurance.
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