The Lactate Threshold (also known as maximum lactate steady state [MLSS], anaerobic threshold, or onset of blood lactate accumulation [OBLA]) represents the point at which blood lactate begins to rise above baseline levels during exercise. It is considered to be a good predictor of endurance exercise performance and can be used to prescribe training intensities based on the relationship between blood lactate levels and heart rate.
What is the Lactate Threshold?
The lactate threshold/maximum lactate steady state (MLSS) corresponds to the exercise intensity at which there is a measurable increase in blood lactate levels above baseline values. During relatively low level aerobic activity, blood lactate levels remain low and will not differ significantly from resting values. As exercise intensity increases there comes a point at which blood lactate levels begin to rise above baseline levels. This rise in blood lactate is believed to occur due to increased rates of glycogen break-down (glycogenolysis) and increased conversion of glucose to pyruvate (glycolysis). In essence the lactate threshold represents a point at which the rate of lactate formation exceeds the utilization of lactate during oxidative-phosphorylation.
As exercise intensity is increased above the lactate threshold the production of lactate continues to increase with increasing exercise intensity peaking at around 4-7x higher than baseline levels. 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. As lactate levels rise there is an associated increase in hydrogen ions. If the concentration of hydrogen ions increases significantly it can lead to a reduction in cellular pH, which at a certain level may start to interfere with cellular enzymes, metabolism and may lead to fatigue. It is important to remember that lactate itself does not cause fatigue, and is actually used as a fuel within aerobic metabolism, where it 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 helps to preserve force production rather than diminish force production (Nielsen et al., 2001). So while lactate levels correlate highly with endurance exercise performance, the traditional view, amongst coaches and athletes, that lactate negatively interferes with performance is incorrect, and rather than causing fatigue it appears to be a marker for other processes occurring within the muscle that are the real culprits of fatigue.
The two graphs (right) illustrate the relationship between blood lactate and work intensity. The first graph shows the relationship between blood lactate and running speed and the second shows the relationship between blood lactate and rates of power when cycling. In both cases lactate levels remain low until at a certain work intensity there is an initial rise in blood lactate – for these athletes blood lactate starts to rise at around 17.5kmh (running) and 250watts (cycling). As the running speed or power output increases further lactate production begins to increase at an accelerated rate.
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 including the percentage of type I (slow twitch) muscle fibres (Coyle et al., 1991), and possibly the ratio of type IIa to type IIb fibres (type IIa are a more fatigue resistant form of fast twitch fibre). Other factors that are likely to influence the lactate threshold include mitochondrial size and density, aerobic enzyme concentrations, muscle capillary density, and enhanced fatty acid metabolism. In addition body mass also appears to be an important factor influencing the lactate threshold (Buresh et al., 2004).
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 at a specific lactate value appears to be a more accurate predictor for endurance performance as race distance increases (Roecker et al., 1998).
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).
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 meaning that elite athletes are able to compete at a higher percentage of their VO2max, and hence a faster speed or power output.
Determining the Lactate Threshold
The lactate threshold is normally determined using a graded exercise test in which the speed or work rate is increased in incremental stages. Each stage normally last 3-4 minutes with blood lactate measured at the end of each stage. The maximum lactate steady state is normally measured over longer, separate workloads, lasting 10-20minutes.
Sports Scientists used a number of different methods to determine the lactate threshold including:
- Through visually interpreting the first rise in blood lactate above baseline.
- 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)
- 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.
Once determined the lactate threshold velocity, or power output, can be used to prescribe training intensities to increase the lactate threshold and to reduce the risk of overtraining.
Estimating the lactate threshold using field tests
A number of tests have been proposed to determine the lactate threshold using simple field tests rather than expensive laboratory based tests, including:
The conconi test – a test proposed to be a non-invasive means of measuring 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. Unfortunately, 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 recent 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 trial/races – athletes often use time trials or races (10km running, 30km cycling) as a means of estimating their heart rate or speed at the lactate threshold. 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. A better option is to undertake a 30minute time trial in a non-competitive situation whilst recording the heart rate throughout. 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). To use this method complete a 30minute time trial and record your heart rate over the last 20minutes. Calculate your average heart rate over your last 20 minutes and average your speed, or power, over the time trial. Your average speed/power and heart rate should equate – to a reasonable level of accuracy – with your lactate threshold.
Percentage of maximum heart rate – another popular, but less accurate method, is to estimate your lactate threshold based on a percentage of maximum heart rate (80-90% of maximum heart rate in trained endurance athletes). Another 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.
Training to improve the lactate threshold
There are a number of training methods and intensities that appear to be beneficial to improving the lactate threshold including a high volume of low intensity training, tempo training, high intensity interval training and resistance 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 an intensity of 70-80%MHR and should comprise more than 50% of your total training volume. 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.
High intensity interval training – high intensity interval training (HIIT) involves training above the lactate threshold and typically involves 3-4minute 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 and therefore this type of training should typically make up no more than 5-10% of your training volume. Most athletes find that one of these sessions per week is sufficient and certainly regularly completing two of these sessions per week, greatly increases the risk of overtraining.
Strength/Resistance training – 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, this in turn 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 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 training, high intensity interval training and strength/resistance training.