Can continuous lactate measurement during training improve your performance? With every training session, you disrupt the balance in your body, which results in a response—a phenomenon known as the training effect. The more effectively you train, the more you improve. This is the essence of targeted training.

In this blog, I’ll discuss how continuous lactate measurement can help you train even more effectively. And yes, here’s the disclaimer right off the bat: I fully recognize that training doesn’t always need to be goal-oriented. Enjoyment, ‘playing outside,’ and simply loving the sport are foundational. After all, sports are the most important non-essential part of life. However, the focus of this blog is on training to improve. Even if you head out without a specific goal in mind, each training session will have its effect. The clearer your goal for a session, the better you can execute and later evaluate it. By the end of this blog, you’ll know whether and how continuous lactate monitoring during training can help you in this process.

Lactate measurement during training is becoming increasingly popular. Inspired by the Norwegian model, more and more endurance athletes are tracking their lactate levels during workouts. The Norwegian model simply means monitoring the intensity of your training by regularly measuring lactate and adjusting your workout accordingly. To measure lactate, however, you need equipment. You also have to stop, prick a drop of blood, have it absorbed by a lactate test strip, and wait for your lactate level to be displayed. It’s quite a cumbersome process.

The latest developments now allow for real-time lactate level measurement during training sessions. Interpreting lactate data requires knowledge and experience. To make sense of the data, you need to understand what you’re doing. That’s why I start this blog with an explanation of what lactate is and what you can do with it.

Whether continuous lactate measurement during training is a game-changer for endurance athletes, such as runners and cyclists looking to optimize their performance, is something I’ll leave for the conclusion.

1 Lactate and energy

Just like a car needs to generate energy to drive, an athlete going for a cycling or running workout needs to generate energy as well. A traditional car does this by burning gasoline or diesel in the engine, which then provides the energy that drives the wheels.

The human body has three systems available for generating energy. The first system is anaerobic alactic, which means without oxygen and without lactate production. This system provides energy quickly by converting creatine phosphate, stored in the muscles, into ATP (adenosine triphosphate). You can think of ATP as a rechargeable battery that your cells use to generate muscle contractions and transmit nerve impulses. This system is depleted after 10 to 20 seconds. Great for a sprint, but insufficient for longer efforts.

Your anaerobic lactic energy system is the second way your body produces ATP. Here, ATP is generated without using oxygen. This system is dominant during intense, short-duration efforts of a few minutes where the body needs energy quickly. Think of the 800 or 1500 meters in track and field. The dominant process for energy production in this system is anaerobic glycolysis, where glucose is converted into energy. Let’s take a look at how this works and what role lactate plays in the process.

1a. Anaerobic glycolysis and ATP production

In the anaerobic lactic system, glucose (which is in your blood, or from glycogen stores in your muscles) is broken down through a process called glycolysis. Glycolysis is a series of chemical reactions that split glucose into smaller molecules, releasing ATP in the process. During this process, glucose is converted into a molecule called pyruvate. Each glucose molecule yields two ATP molecules through glycolysis, which is relatively small compared to the amount of ATP generated by aerobic systems. The reactions of glycolysis occur quickly, meaning the body gets energy rapidly. However, this energy production is limited in duration because byproducts are formed that reduce the efficiency of the process.

1b. The role of lactate

In situations where the body has little or no oxygen available (such as during intense, short-duration efforts), the pyruvate formed cannot be passed on to the Krebs cycle (the aerobic system) for further processing. Instead, the pyruvate is converted into lactate. Lactate plays a crucial role here because it allows glycolysis to continue.

1c. Lactate and acidosis

Lactate plays an essential role in the anaerobic lactic system. When you demand a lot of energy for an extended period, lactate can accumulate in the muscles and bloodstream. A common misconception is that lactate itself causes muscle acidosis. However, it is not lactate that causes this, but the buildup of hydrogen ions (H++) released during ATP breakdown in the muscle cell. These hydrogen ions lower the pH of the muscle cell, making the environment more acidic and leading to the “burning” sensation in the muscles. Lactate acts as a buffer that can partially neutralize these hydrogen ions, helping to slow down the acidosis process. There you go—another myth busted.

1d. Aerobic energy production

The Krebs cycle is a crucial step in aerobic energy production within the body’s cells. This cycle takes place in the mitochondria, the ‘energy production factories’ of the cell, and plays a central role in the production of ATP. The Krebs cycle is especially active when sufficient oxygen is available, such as during moderate to low-intensity exercise. However, even during short, maximal efforts like the 800m and 1500m events in track and field, your aerobic energy system is very important. It acts as a buffer to process lactate. Simply put, your anaerobic lactic system is your lactate faucet, while the aerobic energy system serves as the drain for lactate. The better your aerobic system, the better it can process lactate. I’ll explain this in more detail below.

1e. The role of lactate in the Krebs-cycle and the Cori-cycle

We now understand that lactate is produced at high intensity efforts when the body primarily relies on the anaerobic system. During lower intensities and recovery, lactate can be converted back into pyruvate. This happens under the influence of oxygen and in cells that are capable of efficient aerobic combustion. Lactate is then transported through the bloodstream and exchanged via intracellular exchange between fast and slow muscle fibers to the mitochondria, the energy factories mostly found in your heart and in type I muscle fibers. There, lactate is converted back into pyruvate, in a process called the lactate shuttle.

In addition to glucose, fat can also be used as fuel in the Krebs cycle, especially during longer, moderate-intensity efforts when oxygen is sufficiently available. Fat oxidation is a very efficient way to generate energy and produces a large amount of ATP. However, this process is slower than glucose combustion, meaning fat is primarily used during lower intensities or longer efforts.

Lactate can also be transported via the bloodstream to the liver, where it is converted into glucose in the Cori cycle. This process is known as gluconeogenesis. This glucose can then be used again as an energy source for the muscles. It is converted back into ATP and lactate in your anaerobic energy system—beginning a new cycle. Through these mechanisms, lactate can contribute both directly and indirectly to energy production, depending on the intensity of the effort and the availability of oxygen.

It is important to understand that your body always uses a combination of energy systems. A common misconception is that your body only uses fats at low intensity. You can think of the energy production process as a sliding scale, with ‘dominant aerobic energy production’ at one end and ‘dominant anaerobic energy production’ at the other.

Now that we know how the body produces energy and the role of lactate plays, we will explore how continuous lactate monitoring during training can be used to improve the quality of your sessions.

2. Continuous lactate measurement during training: state of affairs

The lactate values you measure in your blood are the net result of lactate production (in your anaerobic system) and lactate consumption (in your aerobic system). That is the lesson from the previous paragraph. Until very recently, the only way to measure lactate was by pricking a drop of blood from the ear or finger.

For this, I use the Lactate Plus. Most importantly during exercise tests, where I determine lactate values after each step. Based on lactate values, heart rate data, speed, and power, one can determine individual training zones and give advice on how to structure your training toward your main goal.

This is primarily a laboratory application. With those reference values, you can then monitor your intensity during training by taking lactate measurements – like in the Norwegian model we discussed earlier. Still, these lactate measurements are always snapshots. Ideally, you’d want to see your lactate levels continuously so you can adjust mid-training.

OnaSports is—at least to my knowledge—the first company to introduce a commercially available continuous lactate monitor to the market. You wear the OnaSports heart rate strap, into which you insert a biosensor. The sensor sticks to your skin and measures your lactate levels via your sweat. Additionally, the biosensor also measures your sodium and fluid loss, giving you insight into your hydration and salt loss. With the 2024 Ironman World Championship in Kona just behind us, this is no luxury.

In addition to OnaSports, K*Watch is also in an advanced stage of launching their continuous lactate monitor. K*Watch uses a biosensor that makes contact with your skin to measure lactate. Their “SkinTaste technology” sensor measures lactate in the interstitial fluid between blood vessels and cells. The Belgian company Idro has also developed a working version of their continuous lactate meter, which, like OnaSports, is based on sweat analysis.

Now, I hear you thinking: Does measuring lactate through sweat give the same values as measuring it in the blood? At this moment, sweat measurements provide different values than blood measurements. This 2021 study is critical of ‘sweat measurement.’ The measurement can be influenced by how much you sweat, your hydration level, and where the sensor is placed. By the way, similar caveats can also be applied to blood lactate measurements.

In this context, it’s important to understand the difference between validity and reliability. Validity means that you are measuring what you intend to measure. Your measurement hits the target. Reliability means that different measurements are close to the same point. If continuous lactate measurement is reliable but not valid, you can still work with it. You’ll just need to use different reference values for sweat lactate compared to blood lactate values. My expectation is that over time—partly due to AI—the measurement methods will become more reliable, and hopefully more valid. But this is not a deal-breaker. What matters is that you get lactate values that you can work with to make your training more precise.

3. Principles for applying continuous lactate measurement during training

How can you use continuous lactate monitoring to improve your cycling and running workouts? Let’s first discuss five principles for using lactate values during training.

1. Reference Values. By regularly measuring lactate during training, you build up reference values. This gives you more context to interpret your training and adjust it accordingly.

2. Optimizing the Training Stimulus. The clearer your goal for a specific session and the better you understand which lactate values correspond to it, the better you can adjust your training based on lactate measurements.

3. Estimating Carbohydrate and Fat Usage During Training and Competition. We earlier learnt that lactate is the end product of carbohydrate combustion. By knowing your lactate values during exertion—and ideally linking them to lactate values measured during a gas exchange analysis—you gain more insight into which mix of carbohydrates and fats you are using during your training. This allows you to adjust your nutrition during training to ensure you have enough energy to complete your workout. (In parentheses: OnaSports is working on adding continuous blood glucose monitoring to the data display.)

4. Dosing Your Race Effort. Continuous lactate monitoring can help you pace your race optimally. The UCI finds it so effective that they have banned the use of continuous lactate monitors during races. However, continuous lactate meters are still permitted during running events and triathlons.

5. Evaluating Training and Competition. By comparing key workouts, you can examine which combinations of intensity, interval length, number of repetitions, and rest lead to the best adaptations. The same principle can be applied to analyse races and optimize your strategy for the next event.

4. Continuous lactate measurement during training: examples

The practical applications of continuous lactate monitoring are numerous. Here are four, each with an example.

1. DIY Exercise Test. By periodically performing a standard test protocol, you can do a DIY effort test at home or on your training location. I already do this with athletes who live abroad and cannot come to Utrecht for an exercise test. Currently, I have them perform a test with a Lactate Plus, and they send me the data for interpretation. With a continuous lactate monitor, this process is simplified, and you can collect significantly more data points.

2. Optimizing Your Zone 2 Training. Optimizing your aerobic system is the foundation for any endurance athlete. The stronger your aerobic engine, the longer you can sustain effort, the better you can process lactate produced by your anaerobic system, and the faster you recover. “Zone 2 training,” a term I adopted from Iñigo San Millán, is the key method for this. In this blog, you’ll read about how Zone 2 training works and how to execute it best. With a continuous lactate monitor, you can stay within the lactate range for this zone and track of you become more efficient over time.

3. Optimizing Your Interval Workouts. Knowing the lactate values associated with different types of intervals allows you to structure your training accordingly. You can also gauge whether you are sufficiently recovered for the next interval. Lactate data also help you to determine when you’ve completed enough repetitions by tracking parameters that make the training most effective.

4. Increasing or Decreasing Your VLaMax. VLaMax refers to your maximum lactate production rate, indicating how quickly your muscles can produce lactate. A high VLaMax is beneficial for short, explosive races, such as sprints and middle-distance events (like the 800m and 1500m in athletics). A lower VLaMax helps improve aerobic capacity and benefits endurance athletes. Depending on the type of your target event, you may want to “tune” your VLaMax during training to the level that is optimal for your goal. With continuous lactate monitoring during training, you can measure your VLaMax values. Then, you can dose the workouts to train your VLaMax to the desired level.

5. The future of continuous lactate measurement

The technology for continuous lactate measurement during training is developing rapidly, and the potential is enormous. I expect that in the near future, more continuous lactate monitors will enter the market. Among them, one or more will likely emerge as dominant players. In addition to reliable values, the key to this will be an app that is adaptive and provides real-time, actionable insights for the user. This app should offer deeper insights into performance progress, integrate seamlessly with other data (heart rate, power, speed, muscle oxygen data), and be intuitive to use.

Interested in buying the OnaSports continuous lactate monitor?

On behalf of Tri-Excellence, I can offer a discount code for the OnaSports CLM —the first and so far only continuous lactate monitor on the market. I’m sharing this without any commercial interest—I paid for my OnaSports myself. The code is: 3in1Sports-15%

This code is valid until November 24, 2024, and applies to both base stations and cartridges.