Athlete running on a treadmill with a VO₂ analyzer mask in a performance lab to measure oxygen uptake and aerobic capacity during metabolic testing.

You’re already doing great work. By measuring VO2 max, you’re capturing the single most important metric in exercise physiology — the one that defines how much oxygen your client can process and how fit they truly are. That alone already sets your service apart from most gyms, coaches, labs and wellness programs.

But as you know, one powerful metric doesn’t automatically mean a complete physiological picture. To individualize training zones, you need thresholds. To optimize weight loss or metabolic health, you need to understand fat combustion rates. And when testing higher-performance clients, the entire anaerobic system — the other half of metabolism — remains invisible, simply because VO2 analyzers can’t see what happens without oxygen.

If you’ve ever looked at a report of an assessment and had that nagging feeling that something is missing, you’re right — and you’re not alone. Many professionals working with VO2-only analyzers feel that quiet frustration of knowing there’s more under the surface, yet being unable to show it to their clients.

The good news: you can change that easily. 

In this article, you’ll learn how adding just one simple metric — blood lactate — lets you unlock the full metabolic profile of your clients without extending your testing time. In 5min – when you have read this article – you will see how lactate and VO2 data compliments each other and create a synergy that unlocks a whole universe of additional insights. 

You’ll discover not only why and how it works scientifically, but also how it transforms your testing from “informative” to truly comprehensive and confidence-building — for you and for the people you test every day.

And when that happens, you’ll feel the difference immediately. You’ll no longer need to gloss over unanswered questions or fill gaps with assumptions. Instead, you’ll feel in control, credible, and proud of the clarity you can provide. Your consultations will feel deeper, your reports will feel complete — and your daily work will feel once again like what it was meant to be: real applied physiology that changes lives.

Before we dive deeper, here’s a quick explainer video.

In just a few minutes, you’ll see why VO2 alone can miss critical insights like fat oxidation, carbohydrate usage, MLSS, and metabolic efficiency — and how combining VO2 + lactate solves it instantly.

👉 Watch the video below to see why thousands of labs and coaches are upgrading their VO2 testing with one simple step:

Now that you’ve seen how VO2 + lactate transforms your testing capabilities, let’s break down the science and workflow behind it — and how you can implement this without adding time, complexity, or equipment hassle.

Keep reading to learn how it works, why it matters, and how to start using this method to deliver truly complete metabolic assessments.

Where VO2-only testing reaches its limits

Infographic comparing VO₂-only testing with VO₂ plus lactate testing. It shows that VO₂-only reveals aerobic capacity and efficiency, but cannot detect MLSS, RER, or FatMax. Adding lactate enables full metabolic assessment, including MLSS, RER, FatMax, carbohydrate and fat combustion, and complete training zone insights.

Every VO2 analyzer tells you how much oxygen your client can take in and use — that’s the engine size of aerobic metabolism. It reveals cardiovascular efficiency, aerobic power, and overall fitness. Measuring VO2 max means you already capture the single most important metric in exercise physiology.

But two of the most wanted and talked-about markers in endurance and metabolic testing still lie beyond what you deliver with VO2-only analyzers based testing.

The first is the maximal lactate steady state (MLSS) — the single most popular marker in endurance sports. It defines the highest sustainable intensity without the accumulation of lactate (and subsequently acidosis) and it is the foundation for setting training zones and evaluating endurance progress. 

Full metabolic test results displayed as performance dials, including VO₂max, VLamax, FatMax, running economy, carbohydrate and fat combustion, available glycogen, anaerobic threshold (MLSS), and lactate threshold 1 (LT1). Demonstrates metrics unlocked by combining VO₂ testing with lactate analysis.

Yet VO2-only tests can’t detect it, because it depends on two metrics: lactate production and lactate clearance. And whilst the lactate clearance is tightly linked to what you already measure – as we are going to explain in more detail below, the MLSS is a metric that oxygen data alone can’t provide.

The second is the Respiratory Exchange Ratio (RER), which indicates how much energy comes from fat and how much from carbohydrates. RER is essential for determining fat combustion rates and metabolic flexibility, and it forms the basis for the ever-popular FatMax metric — the intensity at which fat burning peaks. 

The second is the Respiratory Exchange Ratio (RER), which indicates how much energy comes from fat and how much from carbohydrates. RER is essential for determining fat combustion rates and metabolic flexibility, and it forms the basis for the ever-popular FatMax metric — the intensity at which fat burning peaks. 

So while your current VO2 test already measures the most fundamental metric in physiology, it still leaves out the two that clients ask for most: MLSS and FatMax. 

By integrating simple lactate measurements, you can unlock both — bridging aerobic and anaerobic systems, connecting oxygen with fuel, and offering a truly complete metabolic profile in the very same test.

Lactate: the fulcrum of muscle energy metabolism

To understand why adding lactate changes everything, it helps to look at what lactate really is — and what it isn’t. For decades, textbooks described lactate as a waste or by-product of high-intensity exercise, something the body produces only when oxygen becomes limited. According to that view, if oxygen supply is sufficient, glycolysis ends with pyruvate, and lactate appears only when the system is “overloaded.”

That understanding is now outdated. Research — including findings published in Frontiers in Neuroscience (Rogatzki et al, 2015) — has shown that lactate is always the end product of glycolysis, not only under oxygen deficiency. 

In fact, lactate is not a “waste product” at all; it’s a key fuel. The lactate formed in glycolysis becomes acetyl-CoA (via pyruvate) – the very molecule that powers aerobic metabolism- and enters the mitochondria and thereby fuels the aerobic metabolism. This is also the one and only way how our bodies burn carbohydrates – the carbohydrates (glucose, glycogen) first are transformed into lactate in the glycolysis and then this becomes the fuel – as explained here – for the aerobic metabolism.

Energy system graphic showing carbohydrates breaking down into glucose, producing lactate, which feeds the aerobic energy system. Demonstrates that lactate is a primary fuel source for aerobic metabolism, alongside fats, reinforcing the biochemical link between glycolysis and aerobic energy production.

In other words, lactate is the bridge between the anaerobic and aerobic systems — the connector that allows energy produced in glycolysis to feed directly into oxidative metabolism. It’s not the sign of a system in trouble; it’s the sign of a system at work.

And this is exactly why combining lactate and VO2 data in the same assessment is so powerful. Each tells you about one side of the energy equation:

  • VO2 shows the utilization for oxygen — a direct and proportional measure of how much aerobic energy the body produces.
  • Lactate shows the utilization of carbohydrates — and lactate production rate is a proportional measure of how much anaerobic energy the body produces.

When you bring them together, the result isn’t just “more data” — it’s an amplifying effect. 

Two separate windows on metabolism merge into a single, dynamic view of how your client’s body actually generates, transfers, and uses energy. That’s what turns a standard VO2 test into a complete metabolic analysis.

How combining VO2 and lactate reveals the full metabolic picture

Let’s look at why combining VO2 and lactate creates so many meaningful insights — not by adding complexity, but by connecting the dots.

When you measure lactate in the blood, that number reflects a concentration — how much lactate is present in a given dilution space (hence depends on the body composition on the given day and subject). This concentration depends on two opposing processes:

  1. Lactate production, and
  2. Lactate clearance.

The following graph illustrates how these two processes interact during a step test. While blood lactate (red) reflects the measured concentration, the underlying production (purple) and clearance through aerobic combustion (blue) determine its rise or stability at each workload.

This graph shows the evaluation of a conventional incremental lactate profile test of an agegroup cyclist. X-axis: elapsed time of the test.
A glimpse into the INSCYD algorithm. This graph shows the evaluation of a conventional incremental lactate profile test of an agegroup cyclist. X-axis: elapsed time of the test. Grey bars: workload: these were 8min steps of 40W each. Red dots: measured lactate concentration. Red line: recalculated lactate concentration by INSCYD. Blue and purple dashed lines: the underlying combustion rate of lactate in the aerobic metabolism (blue) and the actual rate of lactate production in glycolysis (purple) – both in mmol per Liter and per minute.

Production is straightforward — the lactate has to come from somewhere, and that “somewhere” is glycolysis. Clearance, on the other hand, happens through oxidation: using lactate as a fuel within the aerobic metabolism (as explained above).

This relationship between lactate clearance and aerobic activity has been well established for decades — for instance, Donovan & Brooks (1983) showed that lactate oxidation is an almost linear function of VO2.

In simpler terms: the higher your aerobic activity, the faster you burn lactate.

If that sounds abstract, consider a practical example.

After hard intervals, you don’t stand still — you keep moving. You do active recovery because you know your legs recover faster that way. Why? Because keeping your aerobic metabolism active allows you to oxidize the lactate that built up during the effort. That’s lactate clearance in real life.

So, the lactate concentration you measure is the result of two opposing flows: how fast lactate is produced, and how fast it is burned.

Educational graphic explaining that lactate concentration results from two opposing processes: lactate production through glycolysis and lactate combustion linked to oxygen uptake (VO₂). Demonstrates that lactate is continuously produced and burned, and measured levels depend on the balance between production and clearance.

Now here’s the key:

  • You measure lactate concentration directly.
  • You know the combustion rate, because it’s proportional to VO2, which you already measure.

That gives you two of the three terms in the equation — concentration and combustion rate — which means it is now possible to determine the production rate. And once you know that, a cascade of insights becomes possible:

  1. Because lactate is always the end product of glycolysis, its production rate directly represents the rate of glycolytic ATP production, i.e. anaerobic energy turnover.
  2. Because glycolysis only uses glucose and glycogen, and one glucose molecule (C₆) becomes two lactate molecules (C₃), knowing the lactate production rate means knowing the carbohydrate combustion rate.
  3. Combining this with the total energy expenditure (aerobic + anaerobic) allows you to isolate fat combustion rates — revealing the true FatMax and the substrate split across intensities.
  4. And finally, because the maximal lactate steady state (MLSS) is defined as the point where lactate production equals lactate combustion, you can now determine MLSS precisely — not as a statistical guess or fixed concentration, but in its pure physiological definition.

In short: once you combine lactate concentration and VO2, you gain access to every major metabolic insight — glycolytic rate, carbohydrate and fat oxidation, metabolic flexibility, and MLSS — all derived directly from physiological first principles. 

This is why adding one simple lactate measurement to your VO2 test doesn’t just give you more data — it gives you a complete map of energy metabolism.

Bringing it all together

By now, you can see how adding lactate transforms your VO2 testing — technically, scientifically, and professionally. And with INSCYD, this transformation becomes fully accessible.

But the real change goes deeper. 

Once you start delivering full metabolic profiles instead of single numbers, you’ll feel different about your work. You’ll no longer have to explain what you can’t measure. You’ll walk into every client consultation with confidence, clarity, and pride — knowing that your testing reflects the complete physiology you’ve always wanted to show.

And while that scientific depth might sound expensive or complicated, it’s not. 

With INSCYD, there’s no additional time or labor involved. In fact, most professionals who add lactate testing see their return on investment double or even triple — simply because they can charge two to three times more for a comprehensive metabolic assessment than for a single VO₂max test.

Everything else is taken care of:

  • Reporting: Fully automated through INSCYD. Within minutes, you can generate a branded, customized PDF report — complete with all metrics, graphs, and client explanations. No data handling, no spreadsheets, no manual work.
  • Training integration: INSCYD automatically provides individual, physiology-based training zones — VO₂max zone, FatMax, threshold, even the popular Zone 2 — all generated instantly and ready to use.
  • Workflow: Seamless, efficient, and aligned with the professional image you want to project.

And if you’ve never taken a lactate sample before — don’t worry, we’ve got you covered. INSCYD provides a comprehensive e-learning course with videos, tips, and best practices so you can learn at your own pace. You’ll see exactly how to take a clean, painless sample and interpret the data with confidence.

We also partner with the most accurate lactate analyzer manufacturers, so you’ll get discounts on consumables and devices — and in many cases, you can even start with the machine for free.

Finally, our team offers free service and consultancy to help you set up your testing routine, interpret your results, and even optimize your business model around it.

You’ll have all the tools, knowledge, and support to expand your service, increase your revenue, and strengthen your professional credibility — all while doing what you love: using science to help people perform, feel, and live better.

Transform Your Testing Into Premium Performance Diagnostics

Add lactate to your VO₂ protocol and immediately unlock new services, higher revenue, and deeper client results.

  • Get full metabolic profile in one test
  • Use the same protocols, same equipment
  • Built on deterministic models and validated through peer-reviewed literature
  • ROGATZKI, Matthew J., et al. Lactate is always the end product of glycolysis. Frontiers in neuroscience, 2015, 9. Jg., S. 22.
  • BROOKS, George A., et al. Lactate in contemporary biology: a phoenix risen. The Journal of physiology, 2022, 600. Jg., Nr. 5, S. 1229-1251.
  • DONOVAN, CASEY M.; BROOKS, GEORGE A. Endurance training affects lactate clearance, not lactate production. American Journal of Physiology-Endocrinology And Metabolism, 1983, 244. Jg., Nr. 1, S. E83-E92.

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