Shownotes

Mark's Background

02:45-

• My name is Dr Mark Burnley, and I am an exercise physiologist at the University of Wolverhampton in the UK.
• At the University of Kent, where I was part of the endurance research group, I developed much work on kinetics oxygen uptake and power duration development. (creation of the 3-min all-out test)
• My research area is on applying mathematical models to physiological data. So, that is where the VO2 kinetics comes from, and the power duration relationship is a mathematical formula, but it has clear physiological correlations.
• I have been looking at the physiological responses concerning critical power in the last ten years. (intensities above and below the critical power and looking at the fatigue responses) Moreover, we address the neuromuscular responses (peripheral and central fatigue)
• More recently, I moved into more clinical settings, evaluating how we can use exercise to treat and manage diseases.

The transition between the moderate and heavy domain

05:12 -

• When thinking in exercise physiology, we think of different exercise intensity domains, and essentially, we have four of them. Of those four, we have two thresholds that can define boundaries between three of those four domains.
• We have moderate intensity, which is below the lactate threshold. Then, we have the heavy domain between the lactate threshold and the critical power. We have the severe domain, which is above the critical power. Finally, we have the extreme domain, which is when you start the exercise and reach a point of task failure before the oxygen kinetics allows you to achieve the Vo2max.
• There is not a threshold that separates severe and extreme (a grey area)
• The most attention in the last ten years is on the critical power. Many of the athletic events occur in that region of the physiological response.
• Most track distance events will occur at or above critical speed or power.
• The marathon is something that occurs in the heavy intensity domain.
• Therefore, understanding where that boundary is essential.
• It is also crucial to know that the first and second thresholds get mixed up in the literature.
• The first threshold is the lactate threshold.
• I see the first threshold as the first and sustained increase in blood lactate during incremental exercise. 
• To obtain this value, you will put a cyclist in an ergometer, and they would start very slowly.
• For example, if you think the athlete's lactate threshold is at 14 km/h, they might start running at 9-10 km/h. At the end of 5-min, runners stop, and you take a blood sample from the fingertip or the earlobe.
• Then, you increase the speed by 0,5-1km/h, and they repeat the process.
• Another advantage of this is that you can take steady-state measurements of the VO2 responses and get the VO2 and HR relationships to go along with it.
• Moreover, now we have a lactate analyser that allows you to measure lactate almost instantaneously to analyse on the fly.
• You will find that lactate will stay around resting levels for the first three/four levels.
• Therefore, blood lactate would be around 1-2 mmol/L.
• As you cross that threshold, lactate will suddenly rise, and it will continue to rise as you increase the speed.
• The first sudden increase in lactate is the lactate threshold.
• The problem is that sometimes you do not have a flat, stable baseline. One time it rises and stabilises, and others will rise and drop and then rise again.
• Therefore, spotting that threshold can be tricky.
• There are many models where you state a particular level where the lactate threshold occurs as an objective way of measuring lactate.
• If you look at the curve, there is some subjectivity in a sudden increase in lactate.
• Is a 0.2 mmol/L increase a substantial increase, or is it normal?
• Therefore, many people try to fit a curve to the lactate response and see where the curve starts to accelerate. Then you come into the problem of what constitutes an acceleration. And all of those parameters affect our measurements.
• Some studies evaluated all the procedures and models used to obtain the first threshold (25 different models).
• Therefore, the lactate threshold is a complicated concept, and we know some markers in the literature (4 mmol/L onset lactate accumulation – the point where blood lactate achieves four mmol/L).
• We know that value for most endurance athletes will be above the lactate threshold, and it will be near the critical power.
• Even then, it will not be an accurate measure of that either. 
• In the past 10-15 years, we decided we would not use the fixed lactate concentrations. You cannot say to a lactate concentration and say that point is the threshold. You would instead look at the shape of the curve.
• Many people think that the lactate threshold is a continuous curve. So, there is a debate on whether the lactate threshold exists in the scientific community.
• I think that the lactate threshold exists because there is a point where blood lactate increases from the resting level.
• There are also other ways of measuring the threshold. You might see the ventilatory threshold or the gas-exchange threshold. 
• These thresholds are potential methods of measuring the same thing.
• The reason is that as soon as lactate concentration increases, there is a carbon buffer. And this buffer induces extra carbon dioxide, and we can detect these changes with gas-exchange equipment.
• The only problem with that is people have different methods of evaluating patterns and data, which is quite noisy.
• Therefore, it is not easy to plot gas-exchange against speed and obtain thresholds.
• We can use ventilatory equivalents to measure ventilatory thresholds. (taking ventilatory values and dividing them by VO2) 
• If that starts to rise, falling for the first steps means crossing the lactate threshold.
• We use the V-slope metric, where you plot carbon dioxide exchange against VO2. The breakpoint is by plotting two lines and analysing the interception between the lines.
• That interception is the V-slope (gas-exchange threshold), where lactate starts to rise.
• Typically, you do an incremental step test of 3-5min stages to evaluate this. If you want to measure the gas exchange, you do a ramp test, where you continually increase intensity.
• With this approach, you get a more rapid evolution of carbon dioxide and a steeper breakpoint where you can measure it more easily.
• Those are the measuring options. However, when you measure it correctly, that value occurs at a low intensity compared to critical power.
• Typically, we see the lactate threshold to occur at 40-60 % of the VO2max.
• The critical power is often 65-80 % of the VO2max.
• The other thing to point out is how you feel after crossing the lactate threshold. You do not notice it, whereas when you cross the critical power, you get a lot more respiratory drive (you cross the respiratory compensation point), where the frequency of breathing increases.
• It is why some people mistake one threshold with another.
• When you say, "I am running at the threshold, "you probably run at the critical power/speed.

Threshold terminology

16:48 -

• FTP and critical power are concepts interchangeably.
• The lactate threshold is what we describe as aerobic threshold or VT1.
• In the past, people would also say that this would be the anaerobic threshold. However, coaches try to separate "thresholds by saying there are two (aerobic for the lactate threshold and anaerobic for critical power).
• Alongside the gas-exchange threshold, we have the lactic acidoses threshold, the same as the lactate threshold.
• We have to be careful because we also have the minimum lactate test. This test attempted to measure the second threshold (critical power or MLSS).
• However, this test did not work well because it depended on how big the increments were and how lactate behaved.
• The best way to understand this is to have the first lactate threshold, where lactate goes from the resting level and starts to rise. And then, we have a second threshold (critical power) and a second lactate threshold because we have a phenomenon called lactate turn-point.
• As lactate rises, it starts to rise more rapidly.
• Andy Jones uses this a lot in athletes, but you do not see this marker in untrained athletes.
• It is not something familiar to see in people that are not highly trained.
• As athletes run or produce high power outputs, the rates at which these things occur pretty quickly.

Recommendations to measure the first threshold

21:03 -

• If you use a standard validated method, it is not crucial the way you do the tests.
• If you do an incremental test, you need to have stages with enough duration for lactate to reflect what is happening at a muscle level.
• Therefore, 3-5 minutes is good. We typically use 4-min stages.
• In athletes, you might use a 3-min stage because they can get to that stage more quickly than untrained individuals.
• If you do a ramp test, you will not take lactate samples anyway because it is a non-steady-state test throughout, so there is no point in taking lactate measures and associating it with power output.
• In that situation, you use a gas exchange. In that sense, you want to do a test that lasts 8-12min, so you do a classic cardiac-pulmonary test, where you get enough data to see the trends in equivalent metrics, Vo2 and VCO2. Then, you measure those using the "V-slope" and detect those changes.
• Regularly, I would go for a ramp test only because you avoid taking lactate samples.
• If you have a well-worked metabolic cart, you might be better with using the gas-exchange method.
• The only issue is that you have to correct your powers because when you measure power output relative to VO2, the point at which you measure that is a delay because it is a non-steady-state test.
• You have to subtract two-thirds of the ramp rate from where the power was.
• For example, if you do a 30 W per minute ramp, you subtract 20 W from where you see that change occur.
•  We know it is accurate because we did experiments where we did 90 % of the gas-exchange threshold or went above the gas-exchange threshold, and we noticed the expected changes in VO2 and VCO2 from changing domains.
• When we do the incremental tests, we only do them until we reach four mmol/L of blood lactate.
• When you reach that level, you will do another stage of the test anyway, and when you measure it, you might already be 6-7 mmol/L.
• You stop the test and go to a ramp test to get the VO2. You change the power increments and ramp it up to the maximum, or you give them a break and do a ramp test on the last power/speed you achieved.
• We used this protocol often, but now we do only the straight ramp test because we have better ergometers and metabolic carts.

Tips for doing lactate tests

25:54 -

• The advantage of doing lactate tests is that you can measure HR, and if you have a metabolic cart, you can measure VO2 alongside it.
• There would be advantages if I were to do this in the field because we have power meters, GPS, and a portable lactate analyser.
• You only need to do five minutes of constant speed with this equipment and start at a relatively low intensity.
• People worry about how long lactate testing lasts. It does not matter how long you go below the threshold, but how much you do above it.
• If you measure this as you go along, you will know when you go above the threshold, and the athletes will tell you when they feel it is getting too complicated.
• If you have 4-6 steps below the threshold is not a problem. When we start the lactate tests, the biggest mistake I see is that people start already too high.
• Even a national athlete would start at 9 km/h. I would even start at the run/walk transition if unsure.
• If they need 15-20 minutes to get to the threshold is not a problem because those efforts will be in the moderate domain. (they will not use up your muscle glycogen because it is low intensity)
• Once they are above the threshold, they will only do 10-15 minutes above that level.
• The other aspect to consider is how much you increase because it is a big jump if you go up by 2 km/h. 1 km/h is what we usually use.
• If we have an athlete that we know, we could even do 0.5 km/h steps because, in that way, you can get much more density around that threshold and be more precise about where it is.
• However, if I were to do a test, I would do increments of 1 km/h and 4-5 min increment stages.

How to interpret a threshold test

30:24 -

• We would always run a session with our undergraduates and give them a list of obtaining the lactate threshold.
• You will text them several points around a specific point where your lactate threshold is.
• The four mmol/L blood lactate is almost above the lactate threshold.
• Some mathematical techniques allow you to obtain that threshold. There is some free software that allows you to do these things.
• One of them is the D-max method, where you look at the maximum deviation from a straight line from the start to the end of the test.
• That method tends to measure critical power rather than the lactate threshold.
•  My advice is to keep it as simple as possible. We go for a sudden increase in blood lactate concentration. (If you can look at an increase in blood lactate visually)
• The other way is by doing the same thing, but by measuring one mmol/L increase in blood lactate. I believe this method is suitable, and it evaluates the lactate threshold in a quantitive manner.
• It might overestimate the threshold, but it is not a problem for the training prescription because you would not recommend riders to train at precisely the lactate threshold anyway.
•  We should keep things as simple as possible with either one of those methods. (using a visual or quantitative method)
• If you are unsure, the best thing you do is ask somebody else.
• We would need two independent reviewers to look at the lactate plot if we were doing this academically. If they disagree, we get a third reviewer.

Example of lactate curve interpretation

34:05 -

• If you have a rise in lactate at 15 km/h, the threshold would be 14 km/h because Andy Jones taught me to be as conservative as possible. (you do not want to overestimate it)
• If you set 90 % of the gas-exchange threshold and miss the threshold by 10 %, you will exercise at or above the lactate threshold.
• You will not "harm" athletes with this approach when training athletes. If they improve, the lactate threshold will increase, and you will continue to see training-induced changes.
• To run in the heavy domain, instead of running at 14 km/h, you would run at 15-16 km/h.
• If the data you input is different from the character of the data you used to determine the threshold, that method will not be suitable for applying to that data.
• There will always be noise in the data, especially if you are testing on the track or the road. And that noise will affect lactate readings at different intensities.
• Therefore, you do not want to stick to a particular curve shape or mathematical model, so visual inspection is also an excellent way to analyse the curves.

Taking samples from the finger or the ear lobe

37:51 -

• The first thought is that it does not matter. The only issue with the ear lobe is that you need to apply a vasodilator to have a good blood flow, but it does bleed well once you puncture the skin.
• What you need is a free flow sample. When you take a blood sample from the thumb, you tend to hold it with your hand and squeeze it.
• You cannot squeeze an ear lobe. You hold the ear lobe, whereas by taking samples with the thumb, you will squeeze, affecting lactate concentration in the cells and the plasma.
• Sometimes, people get annoyed by how many times I puncture their skin, and it is only to avoid squeezing because the wound healed up. That approach leads to more skin damage, which will also change the data.
• I tend to puncture on the thumb side or the side of the middle of the finger. People who have manual labour might have problems doing the work, like pinching in the finger's middle.
• The other thing to do is put your hand in hot water first.
• It will arterialise the sample, so your hand will go bright pink, essentially. You will get a nice free-flow sample without squeezing the finger when you take a sample.
• As they exercise, they will heat up. And you find that the first few stages will be difficult to get blood out if you do not arterialise the sample.
• When I was learning to do this, I often made this mistake. As a result of that, you will have an undulating baseline.
• Therefore, it becomes complicated to spot the first sustained increase in lactate. It is worth warming the hand first and ensuring you do not puncture through the tough skin.
• It does not matter if you use the ear lobe or the finger as long as you do a technique that does not involve squeezing the blood out.

Absolute values of lactate

41:52 -

• Everyone is different in the absolute lactate values, and you might have to understand where that might come from when analysing data.
• The immediate assumption is that those with a high lactate baseline have high twist muscle fibres dominant.
• There may be an element to that in terms of lactate production, but it is more related to regional blood flow and whether the consumption of lactate occurs in other tissues or not.
• We should use the visual inspection because if you stick to absolute lactate concentrations, we might have problems in the interpretation.
• I have seen people with baselines of 2 mmol/L of blood lactate.
• These things point in the same direction you need to inspect visually.

Training applications of blood lactate testing

43:35 -

• If you have your lactate threshold measured, it will give you a landmark where you can set training or exercise above or below that level.
• If you set your training program, below the lactate threshold is zone one training. (LST will be below the lactate threshold)
• We call threshold training (zone two training) the zone between the lactate threshold and your critical power. 
• This zone is where you do your "steady threshold intervals".
• If you are at the top of zone two, it will fatigue you a lot in 20-30 minutes. But if you work close to your lactate threshold, you will still be in zone two, and you could go for a couple of hours.
• If you look at how people run their marathons, they will run slightly above your lactate threshold.
• It means that zone two is not a one-size-fits-all zone concerning its training.
• Zone 3 is above the critical speed. It is where you would do your tempo sessions and your interval sessions.
• Concerning the competition, the lactate threshold is crucial as the duration increases. We know elite marathon runners tend to run at their critical speed.
• It is not the same for everyone because if you are running anything longer than two and a half hours, you will be getting closer to your lactate threshold.
• Therefore, lactate threshold is critical for recreational runners that want to know how fast they can run a marathon.
• The lactate threshold is the ceiling if we move to Ironman distances or extreme endurance events.
• Therefore, you would limit the HR or speed you should not go over during your effort. If you go above your lactate threshold, you will have to deal with its consequences. (you will have to slow down)
• You want to be as conservative as possible in those races.
• In training, you will try to push the lactate threshold as high as possible.

Can we move the lactate threshold independently from the critical power?

48:21 -

• I believe there is not much scientific evidence that it can happen.
• However, that thing is because of short term studies.
• What we can do is analyse how athletes evolve. World-class athletes have "domain compression".
• They have reached their predetermined maximum for VO2max, which the Breaking2 Project showed does not need to be high.
• There are other factors affecting running performance (running economy).
• Once you reach that ceiling, further training-induced changes will have to come from increasing the thresholds or improving your economy.
• Therefore, we see that VO2max stays where it is as power output or speed, and the thresholds will start to rise towards it. (the VO2 at which critical power occurs increases and the same for the lactate threshold)
• It means they are going to get compressed. One will seem to move more than the other because one of the lactates will be closer to the ceiling.

Value of different lactate checks when training

50:50 -

• The only thing that will tell you is what domain level you will be working on during the session.
• Therefore, if you take a lactate sample at the end of a series of intervals, around seven mmol/L, you know the training stress was effective.
• If you exercise at the lactate threshold for long and take a sample at the end, it will be at baseline blood lactate levels if you did it at the correct intensity.
• If it is above that level, you might think you are not as fit as you thought, so you might slightly dial in the intensity.
• It is a blunt instrument compared to a full lactate test because if you increase your lactate threshold, some of the sessions will be close to the lactate threshold, and lactate concentrations at the end will be lower than regular.
• It means you are not getting the same stimulus from that session, and you need to increase the intensity.
• However, you can check that already with heart rate anyway.

LINKS AND RESOURCES:

• Mark's Twitter, ResearchGate, and Youtube channel
• Critical Power and VO2 kinetics with Mark Burnley, PhD | EP#257
• VLaMax, Polarised training, Fatigue and Complexity with Mark Burnley, PhD | EP#331
• Lactate Threshold Concepts How Valid are They? - Faude et al. 2009
• Lactate in contemporary biology: a phoenix risen - Brooks et. al. 2021