How to Improve the Lactate Threshold as a Runner
We often hear runners and coaches speak about running at ‘threshold’. It’s a key buzz-word we see very often. However, there’s a lot of confusion and misunderstanding about what this term actually means and its significance in running.
So in this article, we’ll take a detailed look at what what the lactate threshold is, why it’s important, and how it can be developed through training. We’ll also look at some other definitions or terms used to define threshold intensity or pace, which confusingly don’t always mean exactly the same thing!
It’s worth noting that at points in this article we refer to training zones. Any mention of a specific zone (e.g. ‘Zone 2’) refers to a seven zone model as described in this article.
What is the lactate threshold?
The lactate threshold is the maximum running power, pace or heart rate that can be sustained while blood lactate levels remain constant. Above this threshold, fatigue hits much more rapidly than when running at or slightly below this threshold. So it marks an important tipping point between what’s ‘sustainable’ and what’s ‘unsustainable’.
It’s an intensity that can be maintained for between 30-60 minutes depending on the athlete, and for many people it will be quite similar to 10km pace in a flat road race. Runners who train with a Stryd power meter will be familiar with the term ‘critical power’. This is a similar intensity to the lactate threshold, although not exactly the same. We’ll explain this more further below.
How fast you can run at your lactate threshold is a very strong predictor of endurance performance, and is relevant for both short races lasting as little as 15-minutes, right up to ultra-distance races lasting 24-hours or more. That said, the lactate threshold is most important for races lasting between roughly 30-minutes to 2 hours, since the intensity of these races will be at or very close to the lactate threshold.
What is Lactate?
Most runners are aware of ‘lactate’ or ‘lactic acid’ (a lactate molecule plus a hydrogen ion), which is a substance that’s produced when the body burns carbohydrates to produce energy. Historically, lactate has been considered to be bad and a cause of fatigue. For example, we often refer to the feeling of burning and fatigue in our legs as being a result of lactate or lactic acid build-up.
However, we now understand that lactate itself does not cause fatigue and is not detrimental to performance. In fact, lactate can provide a very useful fuel for the muscles, and can be easily transported between muscle fibres and to other parts of the body to provide a quick source of energy.
The problem with lactate though is that when it’s produced, there are other ‘metabolites’ or ‘by-products’ that are also produced at the same time, and these have been linked with fatigue. A key example is the hydrogen ion, which cases acidity in the blood and muscles and is thought to interfere with muscle function. So although lactate isn’t bad, the levels of lactate in the blood do correlate with fatigue levels and metabolic strain more generally.
This is why lactate testing has been used for decades to understand running intensity and the associated metabolic demand on the body.
At least some lactate is produced at all times, but as exercise intensity ramps up, the levels of lactate in the muscles and blood also ramp up.
The relationship between running intensity and lactate levels looks like this:
Figure 1. Relationship between running intensity and lactate levels.
Understanding the Lactate Threshold
As mentioned above, the lactate threshold is the highest intensity (e.g. pace, power or heart rate) at which lactate levels in the muscles and blood can achieve a stable concentration.
We can see examples of three different running intensities below, and how lactate levels change with time at a 10 min/mile pace (which for this example athlete is below the lactate threshold), at 8.5 min/mile pace (at the lactate threshold) and at 7 min/mile pace (above the lactate threshold).
Figure 2. Lactate concentration relative to time at three different exercise intensities.
In the first two graphs, lactate levels initially rise, but then reach a stable level. However, in the third example, although the exercise intensity is constant, lactate levels never reach a steady state. This means fatiguing metabolites are continually building in the muscles and blood, and fatigue will hit within a matter of minutes (typically 1-20 minutes depending on how far above the lactate threshold you are).
Your own lactate threshold pace depends both on how much lactate you produce, and also your ability to clear lactate.
Let’s take a look at these two key factors in a little more depth…
Lactate Production
The amount of lactate produced at a given intensity comes down to your ability to switch between fats and carbohydrates for energy.
Fats and carbohydrates are the main sources of fuel for the body when running. When the body uses carbohydrates for fuel, lactate and associated fatiguing byproducts are produced. In contrast, fat oxidation does not result in lactate production. This makes fat oxidation the preferable and less metabolically stressful fuel source during running.
The downside of fat is that it’s slow to produce energy. Therefore, as exercise intensity increases, the body must derive increasing amounts of energy from carbohydrates, thereby increasing lactate production.
Your capacity to produce energy from fats is something that can be developed through training. Therefore, it’s possible to improve your fat oxidation ability and reduce lactate production at a given running intensity.
For example, let’s say when running at 9 min/mile, you derive 50% of your energy from fats and 50% from carbohydrates. With training, it would be possible to shift this to e.g. 80% energy from fats and 20% from carbohydrates at the same pace, which would result in much lower levels of lactate production.
This is one key way to help lift your lactate threshold pace.
Lactate Clearance
The other key factor impacting the lactate threshold is the ability to clear lactate, and importantly the associated metabolites linked with the onset of fatigue. This involves transporting lactate out of the contracting muscle fibre to other sites, where it’s either oxidised or used in a process called gluconeogenesis, which is essentially the conversion of lactate back to glucose/glycogen (the body’s main storage forms for carbohydrate). This transport process is often referred to as ‘lactate shuttling’.
Some adaptations that lead to an improvement in lactate transport/shuttling appear to be brought on via high volumes of low-intensity running. However, others appear to be stimulated only via high-intensity interval training, that repeatedly exposes the muscles to high levels of lactate, and challenges the body’s ability to transport and clear lactate (McGinly & Bishop, 2016).
Another key factor that contributes to the ability to clear lactate is VO2max. VO2max is the maximum rate at which you can take on and process oxygen. It directly impacts the amount of lactate that can be oxidised and thus cleared from the muscles and blood. Lactate oxidation is by far the biggest contributor to lactate clearance during moderate to high intensity exercise (as opposed to gluconeogenesis). So, improvements in VO2max can make a significant difference to lactate clearance capacity and thus the lactate threshold.
Running Economy
If we’re thinking specifically about running pace (which of course is the most important thing when it comes to winning races!), then running economy also plays a part in dictating speed at the lactate threshold. If you can improve your running economy, then you could see improvements in your pace at the lactate threshold, without actually changing anything about your lactate production and clearance abilities.
Running economy is the amount of oxygen or energy required in order to run at a certain speed. This comes down to a variety of factors, including running gait, the effectiveness with which muscle fibres are recruited, various genetic factors, and shoe choice to name but a few!
We’ll be writing an article specifically on running economy in the near future, since it’s relevant across a whole range of intensities and not just at the lactate threshold. That being the case, we won’t delve into the intricacies of running economy or how it can be developed in this article.
Lactate Threshold Workouts
Having understood the mechanisms that comprise the lactate threshold, the logical next question is which training methods best work on changing lactate production and clearance.
Let’s take a look at some sessions that can help in this regard…
Reducing Lactate Production
Fat oxidation is performed at the mitochondria within the muscle cells. Therefore, training that promotes both greater mitochondrial density (number and size of mitochondria within the muscles) as well as mitochondrial function (the speed and efficiency of the enzymes involved in the fat oxidisation process) will improve fat oxidation capacity.
Research suggests that the first of these factors - mitochondrial density - is stimulated mostly by training volume, whereas the specific intensity of the session is less important (Bangsbo et al., 2006; Bishop et al., 2014). So any type of running will help to promote mitochondrial density.
In terms of stimulating improvements in enzymes associated with fat oxidation, it’s been suggested that training at a low ‘Zone 2’ intensity may be optimal, since this is an intensity at which fat oxidation rates are maximised (Jeukendrup & Achten, 2001). There’s no conclusive experimental evidence to support or refute this, but the theory makes logical sense.
Training at a Zone 2 intensity also has the added benefit in that it strikes a balance between activating a meaningful proportion of muscle fibres, while also keeping the metabolic and mechanical stress low enough that relatively high volumes of running can be tolerated each week (thereby allowing a bigger stimulus for improvements in mitochondrial density).
Ultimately, fat oxidation capacity will be improved by a range of training session types, but low-intensity Zone 2 runs are probably optimal in most cases.
Improving Clearance
As mentioned above, VO2max is one of the key factors that contributes to lactate clearance abilities. Sessions that help specifically lift your VO2max are therefore a big help when it comes to improving your lactate threshold. This includes improving mitochondrial density and function, as mentioned above, as well as improving the density of capillaries around muscle fibres, which are responsible for oxygen supply and transfer to the muscles, and improving the ability of the heart to pump blood around the body (for more on the factors impacting VO2max, see here).
Training to improve the lactate threshold should also target improvements in so-called ‘lactate transporters’, which are responsible for improvements in lactate shuttling ability.
There are two key lactate transporters: MCT1 and MCT4.
MCT1 is mainly responsible for transferring lactate INTO muscle fibres, and also moving pyruvate (the precursor for lactate) into the mitochondria, where it can be turned into energy. This transporter is mainly found in Type I (aka slow twitch) fibres.
MCT4 is mainly responsible for transferring lactate OUT of muscle fibres, and is largely found in Type II (aka fast twitch) fibres.
Lactate Threshold Workouts
1. Long Slow Distance Run
Session Description: Run for a length of time that challenges your endurance abilities. The precise length of this run will vary from person to person, depending on your current abilities. However, for most people, targeting a run that lasts between 90-mins to 4-hours will be appropriate. The intensity should be kept to a ‘Zone 2’ effort as much as possible.
Scientific Underpinning: This run allows you to accumulate a lot of training time at an intensity where fat oxidation rates are high, and therefore should help stimulate improvements in both mitochondrial density and fat oxidation enzymes, and reduce lactate production. Another benefit of running for a long period in one continuous run is that muscle glycogen levels become depleted, forcing some of the workload to move to higher power muscle fibres, and helping to bring about adaptations linked with improved fat oxidation in these higher power fibres.
Long runs like these also help with lactate clearance, since they contribute to improved VO2max, and help stimulate the ‘MCT1’ transporter (Dubouchaud et al., 2000; McGinley & Bishop, 2016).
2. Reduced Carbohydrate Availability (RCA) Run
Session Description: A run that’s performed either (i) in the morning before eating or drinking anything that contains carbohydrates (ii) later in the day after an earlier hard training session (either run or strength session). The intensity should be kept to a ‘Zone 2’ or ‘Zone 3’ effort level.
Scientific Underpinning: There is some evidence to suggest that training with reduced carbohydrate availability enhances the stimulus for aerobic adaptations, and particularly those that relate to fat oxidation (Van Proyen et al., 2011; Aird et al., 2018; Yeo et al., 2008; Hulston et al., 2010). The evidence is strongest for method (ii) above, although if method (i) is enjoyable and convenient for you, then we don’t see any downside to integrating this in your training, provided you make sure you’re eating enough calories and carbohydrates throughout the day.
3. Zone 3 Intervals
Session Description: A Zone 2 run, incorporating Zone 3 intervals. These intervals can be a range of durations, and you can easily adapt them to suit the terrain. Generally you’ll want to aim for between 20-60 minutes of Zone 3 running per session. Examples might include:
2-4x 15-mins @ Zone 3, with 2-5 mins recovery @ Zone 2
5-10 x 5-mins @ Zone 3, with 1-min recovery @ Zone 2
A nice progression on this session is to incorporate these Zone 3 running intervals towards the end of a long run. This will force you to perform these efforts with depleted muscle glycogen, which increases the stimulus for aerobic adaptations linked with fat oxidation.
Scientific Underpinning: Running at a slightly higher Zone 3 intensity allows for activation of a higher percentage of muscle fibres, while still allowing relatively high volumes of running. Thus, this can be a good session for stimulating mitochondrial and capillary growth within and around higher-power muscle fibres.
These Zone 3 sessions should be used with some caution though, since Zone 3 running can be both metabolically and mechanically stressful on the body, and therefore we wouldn’t recommend doing a session like this more than 1-2 times per week in most cases.
3. Long VO2max Intervals
Session Description: After a thorough warm-up (at least 15-minutes, incorporating some higher-intensity running to elevate breathing and heart rate), perform a set of long VO2max intervals. These can be structured in various ways, but some common examples include:
5x 6-mins @ low Zone 5, with 3-5 mins recovery @ Zone 1
4x 8-mins @ low Zone 5, with 5 mins recovery @ Zone 1
With each of these sessions you should see your HR reaching or exceeding 90% of your Max heart rate.
Scientific Underpinning: These efforts rely on a phenomenon known as the ‘VO2 slow component’. By running slightly above your lactate threshold, your oxygen consumption will slowly drift up towards VO2max. Efforts like these (as opposed to shorter VO2max efforts) can allow notable time to be spent close to VO2max for a lower subjective effort (Seiler & Sylta, 2017), as well as helping develop your tolerance to high lactate levels, and allowing a higher volume of high-intensity running overall (important for mitochondrial and capillary growth).
4. 2-Min Repeats
Session Description: After a thorough warm-up (at least 15-minutes, incorporating some higher-intensity running to elevate breathing and heart rate), perform 5-15x 2-min efforts @ Zone 5, with 1-min recovery @ Zone 1.
Scientific Underpinning: These efforts repeatedly elevate lactate levels within the blood and muscles with each 2-min hard effort, and then the body must work to clear this lactate quickly with each 60-second recovery. This has been shown to bring about improvements in lactate transporters, and particularly MCT4, which requires high-intensity running in order to develop (McGinly & Bishop, 2016).
Fractional Utilisation
One concept to be aware of when thinking of your lactate threshold is the idea of ‘fractional utilisation’. This is the percentage of VO2max that can be utilised before the lactate threshold is crossed.
So, for example, if VO2max is 60ml/kg/min, and at the lactate threshold oxygen consumption is at 54ml/kg/min, then fractional utilisation would be 90%.
In untrained athletes, fractional utilisation is typically in the region of 50-60%, and for moderately trained endurance athletes, in the region of 65-70%. For highly-trained and elite endurance athletes, this can get as high as 80-90% (Sjodin & Svedenhag, 1985).
For many trail and fell running disciplines, having a relatively high fractional utilisation is desirable, because this effectively means that a higher proportion of the VO2max can be accessed and utilised for an extended period of time. Or in other words, you’re able to tap into a bigger proportion of your available aerobic engine.
One way of thinking about the lactate threshold, therefore, is that VO2max sets the ceiling on how high the lactate threshold can get, and then fat oxidation, running economy and lactate transport abilities all combine to dictate where the lactate threshold ultimately sits relative to VO2max.
An illustrative example of this is shown below, for a two runners with identical VO2max but different lactate threshold paces, resulting from differences in fat oxidation, running economy and lactate transport capabilities.
Knowing your fractional utilisation is useful as it can tell you whether you need to work on your aerobic capacity, or focus on things like fat oxidation and lactate transport in order to see further improvements in your lactate threshold.
Fractional utilisation can be assessed in the lab. However, a nice home-based test is to compare your heart rate when running at your lactate threshold with your maximum heart rate:
If threshold heart rate is around 80-85% of your max heart rate, then your fractional utilisation is low;
If threshold heart rate is around 85-88% of max heart rate, then fractional utilisation is moderate;
If threshold heart rate is around 89-93% max heart rate, then factional utilisation is high.
You can obtain an estimate of your lactate threshold heart rate by performing a 30-minute time trial as described here. Alternatively, if you have heart rate data from a set of races lasting roughly 40-60-minutes, then you can take the average heart rate across these races and this will be a good approximation of your lactate threshold heart rate.
It’s worth noting that having a high fractional utilisation is not always best, since it can come at the expense of your ability to produce shorter, sharp bursts of speed or power (such as might be needed to crest a steep hill, or put some distance between you and a competitor). Generally-speaking, the longer the event, the higher you want your fractional utilisation to be, whereas shorter events (e.g. a short, sharp fell race) would benefit from a slightly lower fractional utilisation.
Other Thresholds
It's worth noting that so far we’ve focussed exclusively on the lactate threshold, or more specifically the maximal lactate steady state. It’s worth noting that there are other thresholds that you’ll encounter in running, and these are not always exactly the same. Below, we’ve summarised some of the key terms you might come across so you can better understand any training advice that uses these terms!
Aerobic Threshold. This is a threshold that occurs at a notably lower intensity than the lactate threshold we’ve been discussing in this article. It can be defined in several ways, such as via measures of lactate levels, breathing rate, or the concentration of expired oxygen and carbon dioxide. It broadly defined the point where the relative energy contribution of fats begins to fall and is replaced by an increasing reliance on carbohydrate oxidation. It can be used to define the top end of Zone 2 in a seven zone model.
First Ventilatory Threshold (VT1)/First Lactate Threshold (LT1): These terms can also be used to refer to the aerobic threshold as defined above. The difference in terminology comes down to how the threshold is measured (e.g. based on lactate levels or breathing).
Critical Power. Users of the Stryd power meter will be familiar with the term ‘critical power’. It defines a transition point where exercise moves from being ‘sustainable’ to ‘unsustainable’, based on a mathematical model of the way that maximal running power decays with increasing duration. This is a topic we’ll write about more in the near future. However, for now, it’s helpful to understand that critical power is a very similar intensity to the lactate threshold, and broadly tries to capture the same thing, but usually sits at a slightly higher intensity.
OBLA (Onset of Blood Lactate Accumulation). This is a term used to describe the intensity at which we see a marked uptick in lactate levels when performing a lactate ramp test (i.e. the point marked with the dotted line in Figure 1 above). It can be used to get an estimate of where the maximal lactate steady state sits, but it’s not precise and can be highly influenced by the specific testing and analysis protocol used.
Second Ventilatory Threshold (VT2). This is a term used to describe the intensity at which breathing dynamics change due to an increased reliance on anaerobic energy systems and an insufficient oxygen supply to meet energy demand. It occurs at an intensity very close to the maximal lactate steady state or lactate threshold.
Anaerobic Threshold: There’s no clear-cut definition for this term, and you might find it used to interchangeably refer to MLSS, OBLA or VT2.
Final Considerations
It is worth mentioning that alongside production of lactate and clearance of lactate is the concept of lactate “tolerance”, which can encompass everything from an individual’s pain threshold and the “buffering” of the accumulating hydrogen ions when above the lactate threshold.
Training for long durations at the lactate threshold will help accustom an athlete to the discomfort associated with elevated muscle and blood lactate concentrations.
Supplementation with beta alanine and sodium bicarbonate can also have an ergogenic (i.e. performance-enhancing) benefit. These supplements improve the ability to ‘buffer’ (i.e. effectively neutralise) the hydrogen ions associated with lactate production. This allows an athlete to ride for longer and with less discomfort at a given lactate concentration.
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