Lactate Testing For Cyclists Explained
Using lactate as a performance measure offers a number of benefits over just power and heart rate data alone (e.g. FTP testing or power profiling).
In this post, we will explain the key insights that lactate testing can provide, and how this can be used to guide your training, including some case studies demonstrating use of lactate data in practice.
Whilst blood lactate testing has typically been associated with a costly and time-consuming visit to a sports laboratory, we will also explain how it is now possible to conduct repeatable, convenient and cost-effective lactate testing at home. If you’re looking for step-by-step guidance on how to perform lactate testing, check out our protocol guide here.
Let’s start by making sure we understand exactly what lactate is and then dive right into the benefits that testing can provide...
What is lactate?
Lactate is produced when carbohydrates (in the form of glycogen or glucose) are broken down anaerobically (without oxygen) to produce energy, in a process called ‘glycolysis’. The end-product of this reaction is a substance called ‘pyruvate’. Some of this pyruvate is then transported into the mitochondria of the cell, and processed by the aerobic energy system to produce more energy, plus some innocuous water and carbon dioxide.
The remainder of the pyruvate is instead converted into a substance called lactate and some other metabolites. Lactate then typically enters the blood stream, where it’s transported to other cells in the body and oxidised to produce energy.
Lactate often gets a bad rap, as many people think it’s the substance that causes fatigue in high-intensity exercise. However, while the mechanisms contributing to fatigue in exercise are still unclear, it’s now thought that it’s the metabolites that are produced alongside lactate that contribute to fatigue, rather than the lactate itself. It’s thought that these metabolites signal to the central nervous system that a metabolic steady state has been exceeded, and that exercise intensity needs to be reduced.
In contrast to previous thinking, it’s now accepted that lactate itself is a positive product of glycolysis. Not only does it act as a signal to trigger helpful physiological responses (such as increased heart rate), but it is also an important source of fuel that can be directly oxidised in mitochondria to produce energy, or can be converted back to glucose or glycogen for later use.
Lactate can be easily measured in the blood, using a small finger-tip sample of blood, and can tell us a lot of information about the metabolic processes that are going on in the body.
Lactate And Training Intensity
The amount of lactate in the blood is dependent on how much lactate is produced, and how quickly it’s cleared. Both of these factors are influenced by exercise intensity.
First of all, you may know that energy is almost entirely derived from either fats or carbohydrates during exercise (there are some minor exceptions, but they aren’t relevant here). Generating energy from fats is slower than from carbohydrates. So as exercise intensity increases, a greater proportion of energy is generated from carbohydrates, via glycolysis, leading to a higher lactate production rate.
In other words, as exercise intensity increases, the rate of lactate production also increases due to increased glycolysis.
Secondly, lactate production and clearance also depends upon the availability of oxygen relative to demand, which is itself dependent on exercise intensity. When exercising at really high intensities, oxygen supply cannot meet demand, and a greater proportion of the pyruvate must be converted into lactate rather than being oxidised directly. Furthermore, due to the limited oxygen availability, the accumulating lactate cannot be oxidised, and therefore cannot be cleared from the blood and muscles unless exercise intensity is reduced.
In other words, at higher exercise intensities supply of oxygen to the working muscles cannot meet demand, and rates of lactate production begin to exceed the rate at which they can be cleared, leading to an exponential increase in the rates of lactate production.
These two factors give rise to a fairly distinctive relationship between lactate and intensity, which can be divided into several zones as shown:
In Zone 1, energy production is largely met by fat oxidation, and the contribution from glycolysis is negligible. Lactate levels are therefore approximately constant and do not increase with exercise intensity (this is a slight simplification, but the details are beyond the scope of this article). Zone 1 is the intensity range in which you’d usually do a long endurance ride.
In Zone 2, glycolysis starts to make a larger contribution to energy production, because fat alone cannot produce energy fast enough. In this zone, lactate levels rise linearly with exercise intensity. However, oxygen supply is still sufficient to clear lactate at the same rate at which it is produced. Therefore, at any given exercise intensity, lactate levels will stay constant.
This means intensities within Zone 2 can be sustained for a long time, but might be a little more uncomfortable than they would be in Zone 1, due to the elevated lactate levels (or more particularly the associated fatiguing metabolites). The higher exercise intensity will also contribute more overall stress and damage, which is why you’d typically look to moderate the amount of training you do in Zone 2, which is often referred to as the ‘Tempo’ or ‘Sweetspot’ zone.
In Zone 3, lactate levels begin to rise exponentially. At this point, oxygen supply cannot meet demand, and lactate production begins to exceed clearance. At any given Zone 3 intensity, lactate levels will rise despite power being held constant, and thus intensities in this zone can only be sustained for a relatively short time. These are the intensities that you’d typically train at during an interval session.
Measuring lactate can therefore be a useful method for defining training zones. These zones are tied to actual metabolic conditions within the body, and thus can have better physiological validity than zones based on FTP or heart rate anchor points (e.g. max heart rate).
The cut-points between these zones have various names, with the lower cut point often referred to as the aerobic threshold or LT1, and the upper cut-point being referred to as the anaerobic threshold, the lactate threshold, the maximal lactate steady state (MLSS), onset of blood lactate accumulation (OBLA) or LT2 (some of these terms have subtly different definitions, but for the purposes of this article, we will treat them as meaning the same thing). FTP is a field-based estimate of LT2, which does not involve lactate testing, and typically tends to over-estimate LT2.
Lactate And Fitness Profile
Not only do lactate concentrations depend upon exercise intensity, they also depend upon an athlete’s unique physiology and fitness level.
Two key variables dictate how lactate levels vary within a given individual. These are:
VO2max (also known as aerobic capacity)
This dictates the maximal rate at which oxygen can be supplied to the working muscles, and thus the point at which lactate production exceeds the body’s capacity to clear lactate (i.e. LT2).
The maximal glycolytic rate (also known as lactic power or glycolytic power)
This is the maximal rate at which energy can be produced though glycolysis. It’s thought that a higher maximal glycolytic rate often correlates with a greater the tendency to produce energy via glycolysis across the spectrum of intensities (although this isn’t always true at an individual level). Thus, for two individuals with the same VO2max, lactate production rates will typically be higher in the individual with the higher maximal glycolytic rate, typically (but not always) leading to a lower LT1 and LT2 power in this individual.
Given that lactate is a product of glycolysis, the maximal glycolytic rate can be approximated by measuring the rate at which lactate is produced during a short, maximal effort (10-30S). This is referred to as VLaMax (the maximal lactate production rate). It’s measured as the rate at which lactate concentration increases in the blood per second (mmol/L/sec).
Bringing these two factors together, we can say that LT2 is a balance between VO2max and VLaMax, as illustrated in the figure below. If VO2max increases relative to VLaMax, LT2 generally increases. If VO2max decreases relative to VLaMax, LT2 generally decreases.
VLaMax values typically range from 0.2mmol/L/sec to 1.0mmol/L/sec. For most endurance sports, it’s been suggested that you’d want this to ideally sit somewhere between 0.3mmol/L/sec and 0.5mmol/L/sec (the lower end for more steady-state disciplines, and the higher end for more punchy disciplines).
However, VLaMax can be hard to measure with precision and reliability because it requires the athlete to produce a maximal sprint, depends upon discrete measures of blood lactate concentrations (meaning the true maximum lactate level can be missed) and is very sensitive to factors such as nutrition and fatigue.
As the lactate sample is also taken usually at the finger or earlobe, which is relatively distant from the site of production (i.e. leg muscles), any resulting measures will also be influenced by factors such as lactate transport/shuttling ability, and total blood volume.
Thus, any measure of VLamax will only ever be approximate. Additionally, the ‘optimum’ VLaMax will depend on the athlete’s aerobic capacity, with a high VO2max allowing a higher VLaMax to be tolerated while still maintaining a good endurance and threshold power. Thus in practice, we don’t think these precise VLaMax targets are overly useful. We prefer to test VLaMax just to get a broad picture of whether this appears to be generally high, medium or low.
Other Factors
There are also some other factors that can impact lactate levels, including the ability to use fats to produce energy, which is dependent on things like mitochondrial density, and oxidative enzyme activity.
Lactate transport (i.e. the ability to move lactate out of the working muscle fibres to other parts of the body) also impacts the lactate-power relationship. A highly active muscle fibre (e.g. in the leg) might already be working at an intensity where oxygen supply cannot meet demand. If lactate could not be transported out of the cell, it would quickly accumulate. However, by improving the ability to transport lactate away from the working muscles to other parts of the body, where oxygen is more plentiful, this allows more lactate to be oxidised. Thus, an improved lactate shuttling can lead to lower lactate levels at a given exercise intensity.
Let’s take a look at some lactate profiles for people with differing fitness parameters:
Example 1
This first example shows two athletes with very similar maximal glycolytic rates and propensities to use fats for fuel. This is indicated by their similar VLaMax values and lactate concentrations at low intensities (similar LT1 powers). The big difference between these two athletes is their aerobic capacity. Athlete 1 (orange) has a lower aerobic capacity, meaning the point at which lactate production exceeds lactate clearance (LT2) is at a lower intensity.
Example 2
In this example, both athletes have a similar aerobic capacity, but athlete 1 (orange) has a higher VLaMax, which results in higher lactate values across the spectrum of intensities, and lower LT1 and LT2 powers.
As can be seen from the above, lactate testing can be used to help understand an athlete’s unique physiological parameters – in particular their aerobic and anaerobic capacities.
Let’s now take a look at some examples of how lactate testing can be used in practice.
Case Study: Assessing Change Over Time
One key benefit of lactate testing is the ability to assess and unpick physiological changes within an athlete over time. We can see this in the example below.
Example 1
In this example, an athlete was tested on two occasions (first = orange, second = blue). On both occasions, the athlete had a very similar VLaMax, indicating that there was probably no significant change in the athlete’s maximal glycolytic rate.
However, the athlete’s LT1, and particularly LT2 powers appear to have increased, with his lactate curve broadly shifting to the right. This might be explained by an improved aerobic capacity resulting in a reduction in lactate production and an increased capacity to clear lactate. We can therefore conclude that the athlete’s recent training has probably been effective at improving aerobic capacity.
Let’s look at a second example:
Example 2
Similarly to the first example, in this second example, LT2 has again improved.
However, in this example, VLaMax has decreased by a notable amount. Assuming there are no obvious confounding variables (e.g. the athlete was notably fatigued or under-fuelled on the second test day, and was similarly hydrated) it appears likely that the vast majority of the improvement in the athlete’s LT2 power is due to a decreased rate of glycolysis. There may have been a change in the athlete’s aerobic capacity, fat oxidation or lactate shuttling ability, but this was probably small, given the large apparent change in VLaMax.
If we were to conduct an FTP test with the athletes in examples 1 and 2, we’d have seen an improved FTP, but we’d have had no idea what physiological changes have caused this, and thus how the athlete has responded to the training. This clearly illustrates a key benefit of lactate testing in allowing us to better unpick the physiological adaptations occurring ‘under the hood’. The testing is not perfect by any means, but it provides some additional information beyond power testing alone.
Case Study 3: Assessing Clearance Rates
So far, we have focussed on the lactate curve and VLaMax. One further piece of information we can look at, however, is the lactate clearance rate. This can give us additional information about improvements in VO2max and/or lactate shuttling ability.
After a hard effort that produces a high level of lactate, we can measure lactate concentrations over time, producing a graph like this:
The faster the lactate clears, the better the lactate clearance abilities. In the graph above, the orange line represents better lactate clearance, and might suggest an improved VO2max or ability to shuttle lactate (we can infer where this change might have come from by looking at the type of training the athlete has been doing and any evidence for changes in VO2max from the other lactate tests discussed above).
Lactate Testing vs Power-Based Testing (e.g. FTP)
At this stage, you may be wondering whether lactate testing is necessary, or whether similar physiological inferences could be made from power-based testing. Power-based testing is common in cycling, whether this is testing FTP via a time-trial or ramp test, or testing power over a range of durations (typically around 5 seconds, and 1, 5 and 20 minutes).
While useful, these power-based tests have some key limitations when compared with lactate testing:
1. Power is always generated by a combination of energy systems.
This means that, if increases or decreases in power are seen, it’s not possible to tell which energy system is responsible, and thus what physiological changes have occurred.
For example, while the 1-minute test is often interpreted as representing anaerobic power, there is still a considerable contribution from the aerobic energy system. Thus, an improvement in 1-minute power could be due to an improvement in either the anaerobic or aerobic energy systems.
Likewise, the 20-min test is typically used to estimate FTP and/or infer changes in LT2. However, an improved 20-min power could actually be due to an increased anaerobic power, which would usually act to reduce LT2! In other words, the results of the 20-min test could lead us to believe the opposite of what’s actually occurred.
In contrast, lactate testing can give us a better understanding of what processes are going on in the body at different intensities, and what changes are occurring over time, because lactate levels are more closely linked to metabolic processes within the body.
2. Zones based on power testing are typically generalised
Most people will set their training zones and interval intensities based on fixed percentages of FTP. For example, using the classic Coggan zones, VO2max intensity would be defined as 106-120% FTP. However, these training zones do not hold true for all athletes.
Using lactate testing can allow for training zones to be individualised based on the actual metabolic processes going on in the body. Some additional testing would be needed to determine some more detailed training zones above the lactate threshold (we’d usually use a combination of perceived exertion, examining heart rate data and using self-paced testing to do that – see here). However, lactate testing provides a good starting point for determining training zones.
Lactate Testing Misconceptions
Given the benefits of lactate testing, it’s perhaps surprising that it’s not more common in training. Here is a summary of some misconceptions of lactate testing and why each need not be of concern:
It’s painful. Actually, the effort level you need to ride at during a lactate test is typically not as hard as when you’re doing a power profile or FTP test. Blood samples for lactate testing are taken from a small finger-prick sample, which causes very little pain.
It requires a lab. In fact, lactate testing can be done out on the road or trail, or on an indoor trainer at home. All you need is a power meter and the lactate testing equipment.
It’s super expensive. While testing in the lab can be quite costly, if you do the testing yourself, it can be very cost-effective and doesn’t need to cost £100s per test. One great way to cut costs further is to split the cost of the lactate analyser (which is the biggest outlay) with friends, so you can all get involved with lactate testing.
It’s difficult to do. Lactate test protocols can actually be as simple as a normal interval workout (often simpler) and lactate sampling is fairly easy after a little practice (although this can depend on the analyser you use).
Home-Based Lactate Testing
Now that most people have access to power meters or smart trainers, it’s really simple to do lactate testing at home, by purchasing a portable lactate analyser and the associated equipment (lancets, lactate strips etc.).
Beyond the obvious benefits of saving time and money, carrying out home-based lactate testing has several benefits over lab-based testing.
First, by doing testing at home, you can use better protocols. The best and most accurate/information-rich protocols require quite a lot of time and resources to perform. They are therefore often not offered by many labs. For example, many labs do not test for VLaMax, and very rarely looks at lactate clearance rates. By testing at home, you can make sure to include these additional tests.
Secondly, testing can be performed using a bike and equipment that you use daily. This will eliminate any problems relating to miscalibration between your power meter and the lab’s equipment. It’s also important because your lactate results can be affected by riding position (because you activate different muscles). Often laboratory bikes can have you in quite an unnatural upright position that’s quite different from your usual riding position.
To help you get started with home-based lactate testing, we’ve produced an article outlining key protocols here. However, below is a very brief summary of the types of protocols you can do at home:
Lactate Profile Step Test. In this protocol power is increased in regular steps, and a lactate sample is taken towards the end of each step. It can be used to plot lactate curves like the ones in this article and determine approximations of LT1 and LT2.
VLaMax Test with Optional Clearance. This test involves riding as hard as possible for around 20-seconds, and then taking lactate samples at regular intervals while resting. This test can be used to identify the peak lactate concentration, and the lactate clearance rate.
Maximal Lactate Steady State Test. This test involves completing several 10-minute fixed-power stages at close to your expected LT2 power. Lactate samples are taken at two time-points within each stage to assess whether lactate concentrations have increased. LT2 can be identified accurately as the highest stage within which lactate did not increase.
Limitations
It’s important to acknowledge the limitations of lactate testing. Lactate monitors are prone to error, particularly if you’re new to lactate testing and/or if you use a lactate monitor that requires large samples of blood or is very sensitive to contamination (e.g. from sweat). This can make interpretation of results hard, because it can be difficult to determine if any measures are erroneous. In our experience, at least three or four rounds of testing are needed in order to confidently understand your lactate profile, and eliminate incorrect readings. Thus, lactate testing is only really valuable if you’re committed to performing this on a fairly regular basis.
Lactate results are also sensitive to numerous factors unrelated to fitness status, such as nutrition, time of day, fatigue, stress, caffeine intake and so on. While you can do your best to control these factors, they will still exert an influence to some degree.
Finally, lactate samples are by no means a perfect measure of what’s going on ‘under the hood’. Lactate is produced at the muscle fibre, and this can then be shuttled to other neighbouring muscle fibres for use as fuel, or transported into the blood stream and then to other parts of the body, where it can be used as fuel or converted back to glycogen. A lactate measure from blood at the fingertip or ear lobe is therefore quite distant from what’s going on metabolically at the working muscle. The measure we see will be influenced by things like total blood volume/body size, how effectively lactate is transported around the body, and how effectively lactate can be metabolised or otherwise cleared, and these factors will differ markedly from person to person. We think that there are better alternatives to lactate testing, such as use of near-infrared spectroscopy to measure muscle oxygen saturation in the muscle capillaries (e.g. using a MOXY device). However, lactate testing remains a relatively cost-effective option and can certainly provide useful insight when better (but more costly/less accessible) options are not available.
Summary
We hope this article has provided you with a good understanding of how lactate data can complement your training, and how home-based testing could provide a convenient means to incorporate this into your training more regularly.
However, if you’d like some more guidance on lactate testing, such as how to pick the right protocol(s) or how to understand the test results, we can provide a number of solutions and advice geared towards helping with this. Please feel free to get in touch if there’s anything we may be able to do to help:
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References
Gray, L. R., Tompkins, S. C., & Taylor, E. B. (2014). Regulation of pyruvate metabolism and human disease. Cellular and molecular life sciences, 71(14), 2577-2604.
Heck, H., Schulz, H., & Bartmus, U. (2003). Diagnostics of anaerobic power and capacity. European Journal of Sport Science, 3(3), 1-23.
Kuphal, K. E., Potteiger, J. A., Frey, B. B., & Hise, M. P. (2004). Validation of a single-day maximal lactate steady state assessment protocol. Journal of sports medicine and physical fitness, 44(2), 132.
Palmer, A. S., Pottinger, J. A., Nau, K. L., & Tong, R. J. (1999). A 1-day maximal lactate steady-state assessment protocol for trained runners. Medicine & Science in Sports & Exercise, 31(9), 1336-1341.