The Lactate Threshold (sometimes referred to as the anaerobic threshold or maximum lactate steady state) is a term used to describe a specific exercise intensity where blood lactate levels begins to rise above above baseline levels.
It has been shown to be a very good predictor of endurance exercise performance and is considered to be a key training intensity for endurance events. The lactate threshold is often used to prescribe training intensities based on the relationship between blood lactate levels and heart rate, speed or power.
In this article we’ll take a look at the science and physiology of the lactate threshold, how to establish your lactate threshold using laboratory and field tests. And take a look how you can improve the lactate threshold through training.
What is the Lactate Threshold?
The lactate threshold corresponds to the exercise intensity where there is a measurable increase in the concentration of lactate in the blood.
During relatively low intensity aerobic exercise, blood lactate levels remain low and do not increase noticeably above those seen at rest. As exercise intensity increases there comes a point where blood lactate begins to rise above ‘baseline’ levels.
As exercise intensity increases further, we start to see an acceleration in blood lactate levels. At this point blood lactate levels are no longer stable and will continue to accumulate even when exercise intensity remains constant.
Speed vs Lactate (Running)
With running we compare speed (kmh) and lactate, or heart rate and lactate.
Power vs Lactate Cycling
In cycling we compare power (watts) vs lactate, or heart rate and lactate.
Why do lactate levels increase?
At rest and during low intensity exercise, blood lactate levels remain relatively stable. Here there is a balance between lactate production and lactate uptake by muscle fibres. As exercise intensity increases we see a rise in blood lactate levels. This rise in blood lactate levels is believed to be due to a number of factors:
- Increased rates of glycogen breakdown (glycogenolysis) and increased use of glucose by muscle cells (glycolysis).
- Increased recruitment of fast twitch muscle fibres.
- An imbalance between lactate production and lactate removal.
1. Increased rates of glycogenolysis and glycolysis
As exercise intensity increases we see increased use of glucose as an energy source. This results in increased production of lactate as an end product of glycolysis.
The traditional view is that glycolysis can result in either the production of pyruvate during aerobic conditions, or lactate in anaerobic conditions. However, we know that lactate production isn’t limited to anaerobic conditions, since lactate is produced both at rest and during low intensity exercise.
2. Increased recruitment of fast twitch muscle fibres
During low intensity exercise, we see the greatest recruitment of slow twitch (type I) muscle fibres.
As exercise intensity increases we start to see increased recruitment of fast twitch muscle fibres. The increased recruitment of fast twitch muscle fibres leads to increased levels of glycolysis and hence increased levels of lactate. A key factor here is the percentage of type 1 (slow oxidative), type 2a (fast oxidative) and type 2b (fast glycolytic) muscle fibres. Athletes, with higher percentages of type 1 and more aerobically trained type 2a muscle fibres can often train at higher intensities before we see significant increases in blood lactate levels.
3. Imbalance between lactate production and removal
Lactate is a fuel than can be metabolised within the mitochondria, in both the slow twitch and fast twitch ‘oxidative’ muscle fibres, during a process called oxidative-phosphorylation.
As well as being metabolised within the working muscles, we also see lactate uptake in the heart, brain, liver and kidneys. As exercise intensity increases we see a point where the production of lactate exceeds the net removal of lactate.
Why do blood lactate levels show an accelerated rise above the lactate threshold?
During low intensity exercise lactate production dose not increase significantly. At these intensities lactate production is balanced by lactate removal.
As exercise intensity increases, there is increased recruitment of fast twitch muscles fibres and higher rates of glycolysis. At a certain point the production of lactate exceeds the removal of lactate by muscle fibres, as well as the lactate uptake within the heart, brain, liver and kidneys. When lactate production exceeds lactate removal we start to see an accelerated increase in blood lacatate levels.
In essence, the lactate threshold represents a point at which the rate of lactate formation exceeds the utilization of lactate during oxidative-phosphorylation.
When exercising above the lactate threshold, blood lactate levels tend to be unstable and will often continue to rise over time, even if the work intensity is kept constant.
Below you can see my blood lactate data for a submaximal cycling test (2019) demonstrating the initial rise in blood lactate levels. You can then clearly see an initial increase in blood lactate followed by a second accelerated increase in blood lactate.
The Lactate Threshold and Endurance exercise performance
The lactate threshold is believed to be an important factor in all endurance events, particularly those lasting over 30 minutes.
Research has found it to be a good predictor of endurance performance in a number of sports including long distance running (Jones and Doust, 1998; Grant et al., 1997; Evans et al., 1995; Yoshida et al., 1993; Morgan et al., 1989;), cycling (Farria et al., 2005; Aunola et al., 2000; Coyle et al., 1991;), rowing (Ingham et al., 2002), kayaking (Bishop D, 2000) and cross-country skiing (Carlsson et al., 2012).
The speed, or power, at a specific lactate value appears to be a more accurate predictor for endurance performance as race distance increases (Roecker et al., 1998).
Lactate isn’t the bad guy
Lactate has traditionally been viewed as a dead end waste product that negatively affects endurance performance. However, research has shown this isn’t the case.
Lactate itself does not cause fatigue, and is actually used as a fuel within aerobic metabolism. In fact, lactate can be oxidized directly, or converted to pyruvate or glucose for oxidation (Philip et al., 2005).
In addition, lactate ions appear to have a protective effect that may help to preserve force production rather than diminish force production (Nielsen et al., 2001). As such lactate is actually an important by product of glycolysis that can be used to fuel aerobic metabolism.
What we do know is that as lactate levels rise, there is an associated increase in hydrogen ions. And as the concentration of hydrogen ions increases, this leads to a significant reduction in both plasma and cellular pH. At a certain level this starts to interfere with cellular enzymes, metabolism and leads to fatigue.
So whilst lactate levels correlate highly with endurance exercise performance, lactate itself isn’t the bad guy. Rather than causing fatigue, it appears to be a marker for other processes, occurring within the muscle, that are the real culprits of fatigue.
Why is the lactate threshold important?
Since the speed or power at which the lactate threshold occurs is related to exercise performance, improvements in the lactate threshold can lead to improved race performance.
It’s known that in elite endurance athletes the lactate threshold tends to occur at a higher percentage of their VO2max. This allows elite athletes to race at a higher percentage of their VO2max, and hence a faster speed or power output.
As such, endurance athletes often use specific training to try to improve the speed, or power, at which the lactate threshold occurs.
The Lactate Threshold and Master Athletes
Interestingly, the percentage of VO2max at which the lactate threshold occurs appears to increase in master athletes (Wiswell et al., 2000).
Although still a good predictor of exercise performance the lactate threshold appears to be less precise than the VO2max, for predicting exercise performance amongst older athletes (Marcell et al., 2003; Wiswell et al., 2000).
This has led to the suggestion that the determination of VO2max, or a recent race performance, may be better for the prescription of training intensities in master athletes (Marcell et al., 2003).
It also highlights how reducing the age associated decline in VO2max may be of greater significance for age group athletes.
Factors that influence the Lactate Threshold
The speed or power at which the lactate threshold occurs, appears to be related to a number of factors.
One key factor is the percentage of type I (slow twitch) muscle fibres (Coyle et al., 1991), and the ratio of type IIa to type IIb fibres (type IIa are a more fatigue resistant form of fast twitch fibre).
We know that over time Type IIa muscle can be trained to become more like Type I fibres. Following a period of endurance training they start to become more aerobically efficient and fatigue resistant. These changes occur gradually over a number of years, highlighting the importance of consistency in training. In fact, after several years of training Type IIa fibres can transform to the point where they are almost identical to Type I muscle fibres.
Any shift in muscle fibre characteristics towards improved aerobic efficiency and fatigue resistance will lead to improvements in the lactate threshold. In turn this leads to an improved ability to sustain high percentages of VO2max during competition.
Other factors that are likely to influence the lactate threshold include:
- Mitochondrial size and density,
- Aerobic enzyme concentrations,
- Muscle capillary density,
- Enhanced fatty acid metabolism.
In addition body mass also appears to be an important factor influencing the lactate threshold (Buresh et al., 2004).
Lactate Threshold Tests
The lactate threshold is normally determined using a graded exercise test in which the speed or work rate (power) is increased in incremental stages. Each stage normally lasts 3-4 minutes with blood lactate measured at the end of each stage.
Determining the lactate threshold:
Sports Scientists used a number of different methods to determine the lactate threshold including:
- Visually interpreting the first rise in blood lactate above baseline.
- Identification of fixed blood lactate concentrations (e.g. 2mMol.l-1 or 4mMol.l-1)
- A specific blood lactate rise above baseline values (e.g. 1mMol.l-1 or 2mMol.l-1 above base line levels)
- An accelerated rise in blood lactate levels – sometimes referred to as LT2 (lactate threshold 2) or the lactate threshold turnpoint.
- The maximal lactate steady state (MLSS) – the highest blood lactate concentration, or work load, that can be maintained without a continual rise in blood lactate levels. Maximum lactate steady state is normally measured over longer, separate workloads, lasting 10-20minutes.
Once determined the lactate threshold can be used to prescribe training intensities, based on the relationship between lactate and heart rate, velocity (running) or power output (cycling, running, rowing).
This can be useful for maximising the benefits of training and reducing the risk of overtraining.
Clearly, there are a number of different ways to interpret the lactate threshold. The most common approach tends to be to identify two specific points:
- The first rise in blood lactate levels above baseline – normally a 1mmol/l rise in blood lactate levels above baseline levels.
- An accelerated rise in blood lactate levels.
When we talk about lactate threshold training we’re referring to exercise between these two points. So what’s the significance of these two points?
1. Lactate Threshold 1 (LT1) – Initial 1mmol/l rise in lactate levels
This represents the point at where we first start to see a rise in blood lactate levels. As we’ve discussed this initial rise occurs due to a gradual increase in glycolysis and fast twitch fibre recruitment.
This intensity represents a point at which most athletes can exercise for around 3-4hours. The importance in knowing this intensity lies in optimising lower intensity endurance training. It represents the upper ceiling for low intensity exercise.
In the chart below you can see how my heart rate during an Ironman Bike segment (180km) falls just below LT1, whereas the heart rate during a half ironman bike segment (90km) is just above LT1 heart rate.
When we train above this intensity we see a gradual transition from aerobic metabolism towards increased anaerobic metabolism. Therefore training just below this intensity represents the upper limit for training that focuses primarily on aerobic metabolism.
2. Lactate Threshold 2 (LT2) – The point of an accelerated rise in blood lactate levels
The second lactate threshold (LT2 or Lactate turnpoint) is the point of an accelerated increase in blood lactate levels. Research has shown this to be strongly linked to endurance exercise performance in events lasting around 60mins (including 10km and half marathons, 30-40k Cycling TTs, Sprint triathlons). Typically, this might equate to around 15-16k running pace in a good level club runner, or around 40k TT power for an equivalent level cyclist.
In terms of training this intensity is often used for longer threshold intervals such as 3 x 10mins at threshold pace (running) or 2 x 20mins at threshold power (cycling).
Once we establish LT1 and LT2, we can use these to set training intensities. This can be particularly useful when using a polarised approach to training. Whilst athletes and coaches often split training into several different training intensities – sometimes 7, or more, different training zones – at it’s most basic level we can characterise training into 3 zones:
- High Intensity
This is based on whether the intensity is below, at the lactate threshold, or above the LT.
Estimating lactate threshold using field tests
A number of different field based fitness tests have been proposed to determine the lactate threshold using simple field tests rather than expensive laboratory based tests.
Whilst, these give an estimate of lactate threshold, it’s important to remember these just provide an estimate, and do not actually measure the lactate threshold.
Some, of the most common field tests for estimating lactate threshold include:
The conconi test
The Conconi test was proposed as a non-invasive means of estimating the lactate threshold (Conconi et al., 1982). The test involves measuring an athlete’s heart rate at increasing speeds or work rates.
The points are plotted on a graph (speed/power vs heart rate) where the heart rate should increase linearly with speed or power until a point of deflection occurs (flattening of the graph) – the point of deflection is proposed to correspond with the anaerobic threshold. However, a number of studies have found the Conconi test to be unreliable and it appears not to be an accurate, or valid, predictor of the lactate threshold (Marques-Neto et al., 2012; Bourgois et al., 2004; Vachon et al., 1999; Jones and Doust, 1997;).
In fact research has identified two heart rate deflection points – found at approximately 40% and 90% of VO2max – and while neither correlated with the lactate threshold the second deflection point was found to correlate with the ventilatory threshold (Marques-Neto et al., 2012).
Time trials or races (10-16km running, 30-40km cycling) can be used as a means of estimating heart rate, speed or power at the lactate threshold.
These can then be used to set training intensities based on heart rate, speed or power.
If using heart rate then an important consideration is that during race situations heart rates tend to be elevated due to increased adrenaline levels which can alter the HR-LT relationship – for most people training at the heart rate achieved in race situations would result in lactate values in excess of the lactate threshold. In this case, a better option is to undertake a 30minute time trial in a non-competitive situation whilst recording the heart rate throughout.
Another consideration with heart is the effects of cardiac drift – where heart rate gradually increases over time, even if intensity remains consistent. As such these sessions are often better controlled by pace or power. Power is particularly effective for controlling intensity when cycling and is now a valid option for runners with technology such as the Stryd footpod.
Research has found the 30-minute time trial method to be a good predictor of velocity and HR at the LT (McGehee et al., 2005). If using this method you can measure your average heart rate, over your final 20 minutes and your average speed, or power, over the full duration of the time trial.
Your average speed/power and heart rate should equate – to a reasonable level of accuracy – with your lactate threshold.
Functional Threshold Power Test (FTP)
An alternative used by many cyclists involves performing a Functional threshold power (FTP) cycling test. There are a number of different ways to estimate cycling FTP; however, the most frequently used test is the 20min FTP cycling test.
So what is FTP? This represents the average power that you can sustain for 60mins. The FTP test essentially involves a 20minute time trial; completed at the maximum effort you can sustain for 20minutes.
During the test you record your average power and heart rate. The average power is then multiplied by 0.95 to give an estimation of FTP. This can then be used to set specific training intensities, using percentages of your estimated FTP.
Critical power (Stryd footpod)
If use the Stryd Footpod then this can auto calculate your 60minute running power. This has the advantage of auto calculating Critical power (CP) based on recent training sessions, race performances or running time trials.
Percentage of maximum heart rate
Another method involves estimating your lactate threshold based on a percentage of your maximum heart rate (80-90% of maximum heart rate in trained endurance athletes). A further variation is to use a percentage of heart rate reserve (HRR) – heart rate reserve is simply the difference between your maximum heart rate (MHR) and your resting heart rate (RHR) e.g. HRR = 200 (MHR) – 50 (RHR) = 150.
You then calculate the percentage of HRR and add the RHR back onto this e.g. 90% of MHR using HRR method = (150HRR x 0.9) + 50 = 135 + 50 = 185. The percentage of heart rate at the lactate threshold can vary greatly so this method is not completely accurate.
Both of these methods are generally the least effective for estimating the lactate threshold. Mainly due to the wide individual variation in the percentage of max heart rate where the lactate threshold occurs.
Training to improve the lactate threshold
There are a number of training methods and intensities that appear to be beneficial for improving the lactate threshold. These including a high volume of low intensity training, tempo and threshold training, high intensity interval training and resistance training.
One of the keys to improving the lactate threshold comes through training that increases the efficiency of muscle fibres to use lactate as a fuel during oxidative phosphorylation – a process that occurs in the mitochondria of type I (slow twitch) and type IIa (fast twitch ‘oxidative’ muscle fibres). A high volume of low intensity endurance training appears to be important for long term development of aerobic efficiency. As such it’s no surprise that most elite endurance athletes include large volumes of low intensity endurance training.
Easy/Moderate aerobic training
Easy/moderate training (aerobic base training) is one of the most important training intensities for the development of the lactate threshold.
It involves training at intensities below the initial rise in lactate threshold (LT1). Typically this would involve training at an intensity below 75% of max heart rate, or ~83% of threshold (LT2) heart rate. This should comprise a minimum of 50% of your total training volume. However, we know that elite athletes typically concentrate 80% of their training in this intensity zone.
Training at this intensity allows us to complete large training volumes and is typically used for mid to long duration training sessions. It’s also the intensity used during the warm up and cool down periods of more intense sessions, as well as during very easy recovery sessions.
Training at this intensity appears to be very important for the development of slow twitch muscle fibres, mitochondrial size and density, muscle capillarization, and aerobic energy production.
Lactate threshold training or tempo training
Lactate threshold training normally involves performing 10-20minute efforts at an intensity that corresponds with, or is slightly below, your lactate threshold. Lactate threshold training improves the ability to sustain high workloads over prolonged periods, can increase the percentage of VO2max at which the lactate threshold occurs and appears to improve the muscle cells ability to utilize lactate during aerobic metabolism.
An example lactate threshold interval session would be 2 x10mins at the lactate threshold speed/power output, or a speed/power that could be sustained for 30minutes, with a 5minute active recovery between the 10minute intervals. Smaller intervals can also be used e.g. 4x5mins although recoveries should be substantially reduced to just 60-90 seconds.
This type of training appears to work well when it makes up around 10-15% of the total weekly training volume. The exact percentage will be dependent on the phase of training and event you are targeting.
High intensity interval training
High intensity interval training (HIIT) involves training above the lactate threshold and typically involves 3-5minute efforts at around 95-100% of VO2max with 90-120 second active recoveries.
Training at this intensity can lead to increases in the velocity or power output at the VO2max which in turn leads to improvements in the speed, or power output, at the lactate threshold. Training at these intensities is very hard, and places the greatest risk of overtraining. Therefore, this type of training should typically make up no more than 5-10% of your training volume. Most athletes find that completing 1-2 sessions of these sessions per week is sufficient, and completing more than two of these sessions per week, greatly increases the risk of overtraining.
Including strength training as part of your endurance training program is an important technique for improving the lactate threshold (Marcinik et al., 1991). This type of training appears to be important because it increases the strength and fatigue resistance of muscle fibres as well as improving exercise efficiency. In turn this can lead to improvements in the speed or power output at which the lactate threshold occurs.
Resistance training appears to be most beneficial when performed 1-2 times weekly –if you are also using high intensity interval training then 1 resistance training session should be sufficient.
Lactate Threshold Summary
- The lactate threshold occurs at a point where there is increased lactate production through glycogenolysis and glycolysis. At a certain point the amount of lactate produced through glycogenolysis and glycolysis exceeds the utilization and oxidation of lactate, at this point lactate levels begin to rise above baseline levels.
- A common misconception is that lactate causes fatigue – this is not the cause fatigue, in fact lactate ions can help to preserve force production. In addition lactate is an important source of fuel that can be oxidized within aerobic metabolism or converted to pyruvate or glucose.
- The lactate threshold is a good predictor of endurance performance in a number of endurance sports including running, cycling, rowing, kayaking and cross country skiing.
- It appears to be of increasing importance with increasing race distance.
- The high correlation between the lactate threshold and endurance exercise performance has led to the measurement of the lactate threshold for monitoring performance as well as for the prescription of specific training intensities.
- The lactate threshold is related to a number of factors including the percentage of slow twitch muscle fibres, mitochondrial size and density, muscle capillary density, efficient fatty acid metabolism and body mass.
- The lactate threshold is normally determine through laboratory based tests. However, a 30minute time trial appears to be a good method for the determination of the corresponding speed or power.
- The best methods for increasing the lactate threshold include a high training volume, tempo/threshold training, high intensity interval training, and strength/resistance training.