Lactate Testing in Cycling: 3 Critical Insights Most Coaches and Labs Are Still Missing

You know the protocol by heart. The cyclist clips in, settles in position and starts pedaling through an incremental test. You draw blood at each stage, track lactate levels, and chart the curve. Soon enough, you’ve got the classic profile: power vs. lactate concentration. From there, you estimate thresholds, prescribe training zones, and maybe even compare it to a previous test to gauge progress. Routine. Familiar. Trusted.

But here’s the thing—just because it’s familiar doesn’t mean it’s flawless.

This method has been around for over 50 years. And while it’s helped shape training plans for decades, it’s worth asking:

“in an era of advanced sports science, skyrocketing knowledge in biomedical sciences and advanced computing power—should we really still rely on a static lactate concentration curve to make critical decisions about performance and progress?”

In this article, we’ll explore three key limitations of conventional lactate testing in road cycling—and how modern science can turn those blind spots into breakthrough insights.

But before we dive in, watch the video to uncover what’s really missing from the lactate profile you’ve been using for years.

In this short video, Sebastian Weber walks you through the three most overlooked limitations of traditional lactate testing in cycling. You’ll discover why the same test result can mean entirely different things—and how relying on curve shifts alone can lead to misleading conclusions for both coaches and athletes.

Now, let’s dive deeper into each of these blind spots—and explore how modern science can transform how you test, train, and track performance.

What Athletes Are Looking For?

Let’s remind ourselves what cyclists are really looking for when they spend their scarce time and significant money on a lactate test.

First and foremost: clarity and confidence. They want to leave knowing exactly how to train—and feel reassured that every hour spent on the bike is pushing them closer to race-day form. Whether it’s prepping for a time trial, criterium, or Gran Fondo, the goal is always the same: make the training count.

Second: relevant benchmarks. Cyclists want to know where they stand—right now. What is their power at race pace? What’s their power at threshold? Are they sparing precious carbohydrates and using fat as fuel? How long can they exercise above threshold? And maybe even more important: how quickly can they recover during a race and at what workload? Are they reaching the intensities that matter for their discipline—whether it’s sustained tempo, repeatability in breakaways, or anaerobic punch for the final sprint?

They need a physiological snapshot that reflects real-world demands on the road.

And third: clear signs of progress. Has the training since the last test delivered the adaptations they were aiming for? Are they moving closer to their goals, or spinning their wheels?

Without that feedback loop, even the most detailed training plan is just a shot in the dark.

You’re looking for several answers—but the lactate curve gives you just one

Let’s take a step back and ask: what are the benchmarks that truly matter in road cycling? For most athletes and coaches, the list is pretty clear:

Threshold power—the cornerstone of pacing and endurance. Especially interesting in races like time trials.
Fuel utilization—how much fat vs. carbohydrate the rider burns, especially crucial in long events like Gran Fondos.
Ability to ride above threshold—how long can a rider sustain power in the red zone, whether in breakaways or bridging efforts?
Recovery during the race—how quickly can they drop their lactate and regain control while still pedaling hard?
Anaerobic and sprint power—those final 15 seconds that decide bunch sprints and attacks.

Now compare that to what a conventional lactate curve actually provides: a visual of lactate concentration plotted against power output. From that, we get an estimate of the threshold. And… that’s it.

No data on fat or carbohydrate combustion. No insight into what happens above threshold. No indication of recovery dynamics. No view into sprint or anaerobic capacity. (Fair enough: if you spent more than 20k on a metabolic cart you will also get one more data point: fat and carbohydrate utilization…still missing out to create the full picture of physiological performance in cycling).

So while the test may look thorough, it’s answering just one of the five key questions that matter to a road cyclist. The rest? You’re left guessing—or assuming that one data point somehow reflects them all.

Tracking progress by the means of a shifted lactate profile curve - what does science tell us?

One of the main reasons cyclists get tested is to track progress. And the go-to method for interpreting change? Look at whether the lactate curve has shifted to the right.

But here’s where things get tricky: a shift in lactate curve tells you nothing about why it shifted.

Let’s unpack this.

Lactate concentration at any given intensity is the result of two competing processes:

Production, which happens in glycolysis—where glucose and glycogen are broken down to form lactate. (1)
Oxidation, which occurs in the aerobic metabolism—where lactate is cleared and burned using oxygen. (2)

Fig. 1: 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.

If production goes up (say, through anaerobic or sprint training), the curve shifts left. If oxidation improves (say, through endurance or VO2max improvements), the curve shifts right. Simple enough.

But here’s the catch: both types of adaptations are common—and even desirable—in road cycling and can happen parallel. More lactate production will mean higher anaerobic power, better sprint capacity, and more punch when attacking or bridging. More oxidation capacity means better endurance, increased fat burning, and improved threshold values.

So what does it actually mean when the curve shifts right? It could be a sign of improved aerobic power… or a loss of sprint capacity and anaerobic punch.

And what about a left shift? It could reflect a powerful, race-winning increase in anaerobic performance… or a drop in aerobic fitness and VO2max.

In both cases, you’re left guessing.

And because most practitioners only look at the shape of the curve—without understanding the changes in lactate production and combustion underneath—it’s dangerously easy to misread the test. A good phase of training can look like failure. A bad one can masquerade as success.

The truth? The direction of the shift tells you nothing—unless you know why the curve moved.

What about the reassurance athletes came for?

Let’s not forget what’s really at stake. Athletes come into the lab not just for numbers—they come for confidence. They want to know their training is working. They want to feel secure that they’re on the right track. They want the satisfaction of seeing progress, or the clarity to make changes if they’re off course.

But after everything we’ve unpacked, we have to ask:

How certain can they be—based on a lactate profile test alone—that they’re actually measuring what matters most? Can they say with confidence how their fat and carbohydrate metabolism is evolving? Do they know if their sprint power and anaerobic capacity are rising or falling? Can they tell if their ability to recover during hard races is improving? Can they track real changes in aerobic capacity?

And when the curve shifts—left, right, or not at all—how sure can anyone be what caused that shift? Was it improved endurance? Lost punch? A balance of both?

The hard truth is this: a performance test that was meant to bring clarity can often leave the athlete with false reassurance—or worse, mislead them entirely. You think the plan is working, so you double down. Or you think it failed, and throw out something that was actually working. Either way, you’re flying blind. And that’s not good enough—not for athletes who are pouring themselves into their training.

Now ask yourself—can you still look them in the eye?

Everything you’ve read so far—about lactate production and combustion, false signals from curve shifts—you can’t unlearn it. You can’t unsee it. The next time you overlay two lactate curves, those doubts will be there. The question will linger: what really changed?

So now, put yourself in the room.

Your athlete just finished a test. The curve shifted to the right. They turn to you, eyes full of hope, trust, maybe even pride. They want you to tell them they’re on track. That the long rides, the intervals, the sacrifices—they’re working.

Can you say that with certainty?
Can you tell them why the curve shifted?
Can you explain what actually changed in their physiology?
Will you feel confident delivering that answer, knowing everything you now know?

And what if the curve shifted left? Can you look them in the face and say they’ve gone backwards—if you don’t know whether it’s from a drop in endurance or a gain in sprint power?

If you charge money for testing—how comfortable will you be handing over a performance report that doesn’t answer the questions your client is truly paying you to answer?

Because here’s the truth: your job isn’t just to collect data. It’s to deliver clarity. To give your athletes a sense of direction, certainty, and confidence. And if the test you’re using can’t do that, then maybe it’s time for a new kind of test.

This is exactly how Sebastian Weber, the founder of INSCYD, felt.

In the early 2000s, Sebastian was working in a human performance lab at a university, testing a mix of amateur cyclists and some of the world’s best pros. He was running textbook lactate tests, plotting curves, calculating thresholds and training zones—doing what everyone else did.

But something didn’t sit right.

Time and again, professional cyclists would complain, post a “great” test result—a classic right-shifted curve—and then go on to have a terrible race. Some even questioned the test altogether: “Why is my performance worse when the test says I’m better?”

And Sebastian didn’t have an answer. Not one he could stand behind with confidence. And he indeed stopped doing lactate profile tests altogether because he wasn’t comfortable administering a test which created such ambiguous results.

Fast forward a decade. After coaching and testing regularly some of the most successful cyclists of the modern era—Tony Martin, Peter Sagan, André Greipel—Sebastian built what he wished he had back then: a tool that could reveal what’s really going on inside the athlete.

That tool is INSCYD.

By combining peer-reviewed science with cutting-edge computational models, INSCYD takes a conventional lactate test and turns it into a complete metabolic assessment.

Using just a few data points—like those collected in the tests you’re already doing—it deciphers the lactate concentration into its two physiological sources:

Lactate production, linked to glycolytic (anaerobic) activity
Lactate combustion, tied to aerobic metabolism

And from there, everything opens up.

You get precise fat and carbohydrate combustion rates across intensities – because lactate production is proportional to glucose utilization and it is involved in the regulation of fat combustion (3). Therefore you can fuel training and racing with surgical precision.

You get actual VO2max values—validated by independent peer reviewed science to be as accurate as those from a lab-grade metabolic cart.

And beyond that, you unlock performance markers that standard testing can’t even touch:

VLamax: the glycolytic counterpart to VO₂max, a key predictor of sprint performance, anaerobic punch, and how an athlete will respond to threshold training.
Lactate accumulation rate: a measure of how quickly an athlete builds lactate above threshold—a powerful indicator of how long they can sustain efforts in the red zone.
Lactate clearance rate (as a function of workload): finally, you can pinpoint how well—and at what intensity—an athlete recovers after attacks, climbs, or surges in the peloton.

Fig 3: Analysis of the ability of an athlete to recover after high intense efforts and the ability to sustain an effort above threshold. Grey line: lactate clearance rate in mmol/l/min. As lactate clearance is proportional to removal of hydrogen ions which cause acidosis and ultimately hamper performance (4,5), the clearance rate of lactate is an accessible and valid marker for recovery. Pink line: rate lactate accumulation above threshold (MLSS) in mmol/l/min. Because in an individual athlete the achieving the individual maximum lactate concentration is valid indicator of exhaustion, the steeper the curve, the quicker athlete will reach fatigue. Hence the pink curve provides a physiology based method to indicate time to exhaustion as function of power output.

In short: you go from guessing why the curve shifted… to knowing exactly what changed. And you go from a single threshold value to all the physiological benchmarks which are relevant to cycling performance as a whole.

You stop interpreting numbers in isolation… and start seeing the whole athlete in a holistic way.

And perhaps most importantly: You can look your athlete in the eye—with confidence—and tell them not just what to do, but why it will work.

Ready to begin? If you’re not yet using INSCYD, book a free demo to take the first step toward integrating physiology-based training into your performance testing and coaching.

And if you’re an athlete, find an INSCYD-certified coach or lab.

Get 360° View of Human Performance with Detailed Metabolic Profile at Your Fingertips

Stop guessing. Start using real physiological data to individualize your clients training and drive consistent progress.

Get everything in one test — revealing the full physiological breakdown that truly drives endurance success.
Use the same protocols, same equipment, same process—just get 10× more insights without disrupting how you work.
Built on deterministic models and validated through peer-reviewed literature, our approach ensures the highest accuracy and reliability.

References

Brooks, G. A. “Lactate: glycolytic end product and oxidative substrate during sustained exercise in mammals—the “lactate shuttle”.” Circulation, respiration, and metabolism: current comparative approaches. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. 208-218.
Rogatzki, M. J., Ferguson, B. S., Goodwin, M. L., & Gladden, L. B. (2015). Lactate is always the end product of glycolysis. Frontiers in neuroscience, 9, 22.
Brooks, George A. “Lactate as a fulcrum of metabolism.” Redox biology 35 (2020): 101454.
Juel, Carsten. “Lactate-proton cotransport in skeletal muscle.” Physiological reviews 77.2 (1997): 321-358.
Juel, C. “Lactate/proton co‐transport in skeletal muscle: regulation and importance for pH homeostasis.” Acta Physiologica Scandinavica 156.3 (1996): 369-374.

Explore Other Blog Posts

Article

Infographic - INSCYD help professional athletes and Time-Crunched amateur athletes

How Time-Crunched Amateur Athletes Benefit from INSCYD

User Stories

In collaboration with renowned coach Frank Pike, we share why and how recreational athletes and age groupers benefit from using INSCYD. Spread the knowledge! Share this article with your fellow coaches and athletes. Click the share buttons below and inspire others on their journey to athletic excellence. Facebook Twitter LinkedIn Reddit Email The challenge of…

Wout van Aert reveals his secret: how to switch from cyclocross to road cycling

Article, User Stories

Cyclocross heroes seem to dominate in road cycling. How do cyclists like Thomas Pidcock, Wout van Aert and Mathieu van der Poel make the switch from a 60-minute cyclocross race to a 6-hour road race? In this blog, Wout van Aert – coached using INSCYD since 2017 – reveals his secret! In cyclocross, it is…

Does the anaerobic threshold really occur at 4 mmol/l blood lactate?

Article

Many performance labs and coaches determine the anaerobic threshold based on a lactate concentration of 4 mmol/l during an incremental test. This article answers whether that is a valid method of assessing the anaerobic- or lactate threshold. Share this insightful article with athletes, coaches, and sports enthusiasts who can benefit from a deeper understanding of lactate…

TrainingPeaks vs INSCYD

Article

This article talks about the differences between a training platform like TrainingPeaks and INSCYD performance software. We also show how teams like Alpecin-Deceuninck combine both tools to prepare their pro athletes for key races. *Although we compare INSCYD with TrainingPeaks, the same is true for other training platforms like Today’s Plan, AZUM, etc. Prefer watching…

Infographic - Peak and Fade (Pre Loaded) Intervals

How Peak and Fade (Pre Loaded) Intervals Can Boost Athletic Performance

Article

Peak and fade intervals are a key component in the training regimens of elite athletes. These Peak and Fade Intervals start at a very high intensity and gradually decrease, offering a unique approach to training. This article not only delves into the science behind Peak and Fade Intervals but also covers pre-loaded intervals, another effective…

INSCYD integrates Heart Rate in Training Zones

Article

We are happy to announce that from now on, heart rate is integrated into our training zones. That means you can now describe a FatMax training zone – or any other training zone – based on heart rate. Image: INSCYD partner Triathlon Training Academy In the past, INSCYD training zones were described based on speed…