Lactate Threshold: The Science, Tests and Training
The Lactate Threshold (sometimes referred to as the anaerobic threshold or maximum lactate steady state) is a term used to describe an exercise intensity where blood lactate levels rise above baseline levels.
It’s an extremely useful predictor of endurance exercise performance and a key training intensity for endurance athletes. For this reason lactate threshold tests are used to establish training intensities, based on the relationship between blood lactate levels and heart rate, speed or power.
In this article we’ll look at:
- The science and physiology of the lactate threshold.
- Different tests you can use to measure it.
- The best approaches you can use to improve it.
WHAT IS THE LACTATE THRESHOLD?
The lactate threshold is an exercise intensity where there’s a measurable increase in blood lactate.
During low-intensity exercise, blood lactate levels remain low and do not increase noticeably above those observed at rest. As exercise intensity increases, blood lactate rises above ‘baseline’ levels.
As exercise intensity increases further, we see an acceleration in blood lactate levels. At these intensities blood lactate levels are no longer stable and continue to rise even when exercise intensity remains consistent.
You can see examples of this in the charts below showing how lactate increases in relation to speed (when running) and power (when cycling).
Why do lactate levels increase?
At rest and during low-intensity exercise, blood lactate levels remain stable. Here there’s a balance between lactate production and lactate uptake by muscle fibres. As exercise intensity increases, blood lactate levels rise. This rise occurs because of several factors:
- Increased 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 rate of glycogenolysis and glycolysis
As exercise intensity rises, 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 results in either the production of pyruvate (during aerobic conditions), or lactate (in anaerobic conditions). However, we know that lactate is not just present in anaerobic conditions – it’s produced 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 observe increased recruitment of fast twitch muscle fibres. This leads to increased rates of glycolysis and hence increased levels of lactate. A key factor here is the proportion of type 1 (slow oxidative), type 2a (fast oxidative) and type 2b (fast glycolytic) muscle fibres. Athletes, with higher proportions of type 1 and more aerobically efficient type 2a muscle fibres, can exercise at greater intensities before blood lactate increases substantially.
3. Imbalance between lactate production and removal
Lactate is a fuel source that’s metabolised within the mitochondria of slow and fast ‘oxidative’ muscle fibres during a process called oxidative-phosphorylation. And this isn’t just limited to skeletal muscles, we also see lactate uptake in the heart, brain, liver and kidneys.
Why lactate accumulates above the lactate threshold
At low-to-moderate exercise intensities, there is a balance between lactate production and removal. As exercise intensity increases, we see a point where the production of lactate exceeds the net removal of lactate.
As exercise intensity increases, there’s increased recruitment of fast twitch muscles fibres. This leads to higher rates of glycolysis. At a specific point the production of lactate exceeds the removal of lactate by muscle fibres, and the uptake within the heart, brain, liver and kidneys. At this point we observe an acceleration in blood lactate concentration.
In essence, the lactate threshold represents an intensity where the rate of lactate production exceeds its usage during oxidative-phosphorylation.
When exercising above the lactate threshold, blood lactate levels become unstable and will often continue to rise, even if the work intensity constant.
Below you can look at my blood lactate data for a submaximal cycling test (2019). Here, you can see how blood lactate remains stable at low intensities, then exhibits a linear rise, followed by a more rapid increase at 325w.
LACTATE THRESHOLD AND ENDURANCE EXERCISE
The lactate threshold matters in all endurance events (particularly those lasting over 30 minutes).
Research has established it to be a strong predictor of endurance performance in several 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).
And appears to be a more accurate predictor of endurance performance as race distance increases (Roecker et al., 1998).
Lactate isn’t the bad guy
We have traditionally viewed lactate 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 – it serves as a fuel within aerobic metabolism. In fact, it can be oxidized, or converted to pyruvate or glucose for oxidation (Philip et al., 2005).
In addition, lactate ions may have a protective effect that preserves force production rather than weakening it (Nielsen et al., 2001). Therefore, lactate is an important by-product of glycolysis that can fuel aerobic metabolism.
What we know is when lactate levels go up, there’s an associated rise in hydrogen ions. And as the concentration of hydrogen ions rises, this leads to a meaningful reduction in both plasma and cellular pH. At a specific level, this interferes with cellular enzymes, metabolism and contributes to fatigue.
So while lactate correlates strikingly with endurance exercise performance, it isn’t the bad guy. And rather than causing fatigue, it appears to be an indicator for other processes, taking place within the muscle that are the true culprits of fatigue.
Why is it important?
Since it’s strongly related to exercise performance, improvements transfer to better exercise performance.
It’s known that in elite endurance athletes the lactate threshold occurs at greater percentages of VO2max. This allows them to exercise at higher percentages of their VO2max, and faster speeds or higher power outputs.
Essentially, it allows them to maximise their performance potential.
For this reason, endurance athletes use specific training to boost the speed, or power, at the lactate threshold.
Interestingly, the percent of VO2 max at the lactate threshold increases in master athletes (Wiswell et al., 2000).
Although still a great predictor of exercise performance, it may be less important than the VO2 max, for predicting exercise performance in master athletes (Marcell et al., 2003; Wiswell et al., 2000).
This has led to the idea that the VO2max may be better for determining training intensities in master athletes (Marcell et al., 2003).
This highlights how slowing the age related decline in VO2 max is of great significance for age group athletes.
Factors that influence the lactate threshold
The speed, or power, at the lactate threshold is related to several factors.
One key factor is the proportion 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 than IIb.
We know that through training Type IIa muscle fibres can transform to be more like Type I fibres. And following endurance training they become more aerobically efficient with greater fatigue resistance. These adaptations develop steadily over several years, underlining the importance of consistency in training. In fact, after several years of training, Type IIa fibres can transform to where they are essentially indistinguishable to Type I fibres.
This change in muscle fibre characteristics contribute to improvements in the lactate threshold. And the capacity to sustain higher percentages of VO2 max during competition.
Other factors that affect the lactate threshold include:
- Mitochondrial size and density,
- Aerobic enzyme concentrations,
- Muscle capillary density,
- Enhanced fatty acid metabolism.
In addition, body mass is an important factor (Buresh et al., 2004).
LACTATE THRESHOLD TESTS
Lactate threshold tests involve using a graded exercise test in which the speed or work rate (power) increases in incremental stages. Each stage typically lasts 3-4 minutes with blood lactate measured at the end of each stage.
Measuring the lactate threshold
Sports Scientists can use several methods to determine the lactate threshold. These including:
- Visually interpreting the initial rise in blood lactate above baseline.
- Identification of fixed blood lactate concentrations (e.g. 2mMol.l-1 or 4mMol.l-1)
- A specific rise above baseline values (e.g. 1mMol.l-1 or 2mMol.l-1 above baseline levels)
- An accelerated rise in blood lactate levels – frequently referred to as LT2 (lactate threshold 2) or the lactate threshold turn point.
- The maximal lactate steady state (MLSS) – the greatest blood lactate concentration, or workload, without a continuous rise in blood lactate levels. They test this over longer, separate workloads, that typically last 10-20minutes.
Once detected, we can 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 training and reducing the risk of over-training.
Clearly, there are several ways to interpret the lactate threshold. The most accepted method is to identify two distinct points:
- The initial rise in blood lactate levels above baseline – normally a 1mmol/l rise above baseline levels.
- An accelerated rise in blood lactate levels.
When we describe 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 rise above baseline
This represents the intensity where we first see a rise in blood lactate levels. As mentioned, this occurs because of a gradual increase in glycolysis and fast twitch fibre recruitment.
This intensity represents a work rate where most athletes can exercise for around 3-4hours. By identifying this we can optimise low-intensity endurance training, since it represents the upper ceiling for low-intensity exercise.
In the chart below, you can look at my lactate profile and average cycling heart rate during a half (90km) and full ironman distance bike segment (180km).
When we train above this intensity, we transition from mainly aerobic metabolism towards increased anaerobic metabolism. Therefore, training just below this intensity represents the upper limit for training where the focus is primarily on aerobic metabolism.
An important point to note is aerobic metabolism continues to contribute significantly at intensities above the lactate threshold (until VO2 max intensity, where it plateaus) – it’s just anaerobic metabolism becomes proportionally more significant as exercise intensity increases.
2. Lactate threshold 2 (LT2) – point of accelerated increase
The second lactate threshold (LT2 or Lactate turn point) is the point of an accelerated increase in blood lactate levels. Research has established its strongly associated with endurance exercise performance in events lasting around 60mins (including 10km and half marathons, 30-40k Cycling TTs, Sprint triathlons). 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, we often use this intensity for longer threshold intervals such as 3 x 10mins at threshold pace (running) or 2 x 20mins at threshold power (cycling).
Once established, we can use LT1 and LT2 to set training intensities. This can be helpful when applying a polarised approach to training.
While athletes and coaches often split training into several training intensities – sometimes 7, or more training zones – at the most basic level we can characterise training into 3 distinct zones:
- High Intensity
We base these on whether the intensity is below LT1 (easy), between LT1 and LT2 (moderately hard), or above LT2 (high-intensity).
Several field based fitness tests have been used to estimate the lactate threshold. These field tests provide a cost-effective alternative to laboratory based tests.
While they provide an estimate of lactate threshold, it’s important to recognize these do not measure the lactate threshold.
Some of the most popular 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.
These are plotted on a graph (speed/power vs heart rate) and heart rate should increase linearly with speed or power until a point of deflection occurs (flattening of the graph). This is said to correspond with the anaerobic threshold. However, several 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 correlates with the ventilatory threshold (Marques-Neto et al., 2012).
Time trials or races (10-16km running, 30-40km cycling) can be used to estimate the heart rate, speed or power at the lactate threshold.
We can then set training intensities based on heart rate, speed or power.
If using heart rate from a race, an important consideration is heart rates are higher during races because of increased adrenaline levels. This can alter the HR-LT relationship. A better option is to undertake a 30minute time trial in a non-competitive situation while recording the heart rate throughout. While, races are less accurate for establishing the heart rate at lactate threshold, you can use races to establish the pace or power at the lactate threshold.
With time trials, 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, measure your average heart rate over your final 20 minutes and your average speed, or power, over the full 30-minute duration of the time trial. Your average speed/power and heart rate should equate – with a good level of accuracy – to your lactate threshold.
Another consideration with heart rate is the effects of cardiac drift (where heart rate steadily increases over time, even when intensity remains consistent). This is one reason we record heart rate over the final 20-minutes of the time trial, rather than the full 30-minute duration. It’s also why lactate threshold sessions are best controlled by pace or power. Power is effective for controlling intensity when cycling and is now a good option for runners with technology such as the Stryd footpod.
Functional Threshold Power Test (FTP)
An option employed by many cyclists involves completing a Functional threshold power (FTP) cycling test. There are several 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 most straight forward FTP test is a 20minute time trial – you complete this at the maximum effort you can sustain for 20minutes.
During the test, you record your average power and heart rate. We then multiply average power by 0.95 to gain an estimation of FTP. From this, we can set specific training intensities, using percentages of your estimated FTP.
Critical power (Stryd footpod)
If using the Stryd Footpod, then this can auto calculate your 60minute running power. This has the convenience 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). This is 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 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, so this method is not altogether accurate.
Both methods are considered less accurate. Mainly because of the wide individual variation in the percentage of max heart rate at the lactate threshold.
IMPROVE THE LACTATE THRESHOLD
There are several training approaches and intensities that are 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 effective approach for increasing the lactate threshold comes through training that increases the efficiency of muscle fibers 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). With this in mind, a high volume of low intensity endurance training is 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 exercise
Easy/moderate intensities (aerobic base training) is one of the most effective training intensities for the development of the lactate threshold.
It involves training at intensities below the initial rise in lactate threshold (LT1). Typically, this involves training at an intensity below 75% of max heart rate, or ~83% of threshold (LT2) heart rate. And 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 you to complete large training volumes and used during mid to long duration training sessions. It’s also the intensity used during the warm-up and cool-down of more intense sessions, and during very easy recovery sessions.
Training at this intensity turns out to be important for the development of slow twitch muscle fibres, mitochondrial size and density, muscle capillarization, and aerobic energy production.
Lactate threshold training typically involves 10-20minute efforts at an intensity corresponding with, or slightly below, your lactate threshold. This improves the capacity to sustain high workloads for prolonged periods, increases the percentage of VO2 max at the lactate threshold and improves the muscle cells’ capacity to use 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’s sustainable for 30minutes (critical velocity), with a 5minute active recovery between the 10minute intervals. We can also use shorter intervals, e.g. 4x5mins combined with short recoveries (ideally to around 60-90 seconds).
This type of training appears to work well when it makes up around 5-10% of the total weekly training volume. The exact proportion will depend on the phase of training and the event you are targeting. For example, a half marathon runner would include more threshold training than a 1500m runner.
High intensity interval training (HIIT) requires training above the lactate threshold. This commonly involves 3-5minute intervals completed at around 95-100% of VO2max with short active recoveries (e.g. 90-120second recoveries). That said, shorter intervals are also effective.
Training at this intensity can increase the velocity or power output at the VO2 max and leads to improvements in the speed, or power output, at the lactate threshold. Training at these intensities is hard, and places a higher risk of over-training. Therefore, this type of training should normally make up around 10-15% of your training volume. Most athletes find that completing 1-2 sessions per week is sufficient, and completing over two per week is less effective.
Including strength training as part of your endurance training program is an effective approach for developing the lactate threshold (Marcinik et al., 1991). This type of training turns out to be effective because it enhances the strength and fatigue resistance of muscle fibers, improves neuromuscular coordination and exercise efficiency. In turn, this increases the speed or power output at the lactate threshold.
Strength training is most effective when performed 1-2 times week – if already using high-intensity interval training, then 1 resistance training session should be sufficient.
- The lactate threshold occurs at an intensity where lactate production (through glycogenolysis and glycolysis) exceeds the usage and oxidation of lactate by working muscles and other organs. When this happens, lactate levels rise above baseline levels.
- A common misunderstanding is that lactate causes fatigue. Lactate itself does not cause fatigue. In fact, lactate ions may help to conserve force production.
- It can be oxidized within the mitochondria or converted to pyruvate, or glucose.
- The lactate threshold is an excellent predictor of endurance performance in several endurance sports including running, cycling, rowing, kayaking and cross-country skiing.
- It becomes of growing importance as race distance increases.
- Lactate threshold intensity is associated with several factors including the proportion of slow twitch muscle fibres, mitochondrial size and density, muscle capillary density, efficient fatty acid metabolism and body mass.
- Lactate threshold tests are effective for monitoring exercise performance, and for the prescription of individual training zones.
- It’s normally established through laboratory based tests. However, a 30minute time trial is an excellent alternative.
- The best methods for increasing the lactate threshold include high-volumes of low-intensity exercise, tempo/threshold training, high-intensity intervals, and strength/resistance training.
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