Lactate Testing: Explained
In this article we will discuss:
Lactate: What is is?
Lactate and exercise intensity / fat oxidation
Using lactate as a guide for exercise zones
Lactate assessments we use/test at First Principles Fitness
What is lactate?
Lactate is produced when carbohydrates (in the form of glycogen or glucose) are broken down anaerobically to produce energy, in a process called ‘glycolysis’. The end-product of this reaction is a substance called ‘pyruvate’ which is transported into the mitochondria of the cell, to produce more energy (ATP). Pyruvate can also be converted to lactate. Under these conditions lactate will either deposit into the bloodstream and be shuttled away or enter the mitochondria to make more energy.
Once in the bloodstream, lactate is transported around the body to be used as fuel or stored as glycogen. Organs such as the brain or heart can use lactate as fuel. When not being shuttled away, lactate can also enter the cells mitochondria and be used by the muscle to create more energy (ATP).
Lactate often gets a bad rap, as many people think it causes fatigue when exercising at intense levels. However, while blood lactate is correlated with fatigue, lactate itself does not directly contribute to fatigue. Lactate, as fuel, actually aids in exercise prolongation!
Think of lactate as a reusable energy source. The better one is at reusing/shuttling their own lactate, the higher intensity one can work out at without fatigue. This would be like if your car could re-use its exhaust gas as a fuel. This exact mechanism is what separates professional endurance athletes from the average person. Professional endurance athletes’ cells reuse lactate more efficiently. Therefore, they don’t need to rely on ATP production outside the cell which would cause more fatigue and lower PH via H+’s from glycolysis.
Lactate And Training Intensity
The amount of lactate in the blood is dependent on how much lactate is produced, and how quickly it’s cleared. Both of these factors are influenced by exercise intensity.
You may know that energy is mainly derived from fats or carbohydrates. Generating energy from fats is slower than from carbohydrates. So as exercise intensity increases, a greater proportion of energy is generated from carbohydrates (glycolysis) leading to a higher lactate production rate. In short, as exercise intensity increases, the rate of lactate production also increases due to increased glycolysis and more fuel from carbs.
Secondly, lactate production and clearance also depends upon the availability of oxygen relative to demand, which is dependent on exercise intensity. When exercising at high intensities, oxygen supply cannot meet demand, and a greater amount of lactate is produced. Furthermore, due to the limited oxygen availability, the accumulating lactate cannot be oxidized, and therefore is shuttled to the bloodstream and not re-used as fuel inside the mitochondria.
To recap, YOUR performance depends on two markers:
How well do you produce energy from fat and NOT carbs?
How well does your body shuttle lactate/mitochondria re-use lactate for fuel?
Both have 1 factor in common. Large, plentiful and practiced mitocondria. You need to have the equipment and the body needs to know how to use the equipment. This is a big reason for zone 2 training (on a 5 zone model). Zone 2 is where you are oxidizing fat for fuel the most and the mitochondria have the highest strain/percentage of fat as fuel. See our article on Maximum Fat Oxidation for more information.
All humans can reuse lactate to make energy, this is our steady state or “Maximal fat oxidation state” . Also the intensity where zone 2 training should be performed. For most individuals this is walking/slow jogging or 100-130 watts on a bike. However, endurance athletes can run as fast as 10 mph or pedal 250 watts on a bike for hours on end! One main reason they can maintain this high output is because of their ability to re-use and shuttle lactate. The more type 1 fibers one has the better they would be at re-using lactate for fuel. Type 1 fibers are rich in mitochondria and dense with capillary beds for o2 exchange/blood flow. As seen in the picture above, lactate from type-2 fibers can be re-used in the mitochondria of type 1 fibers. This is how endurance athletes can output so much power without hitting a wall. Their fast twitch fibers are working at a high intensity and using carbs for fuel but the type 1 fibers are picking up the by product “lactate” and using for fuel so it doesn’t enter circulation.
When lactate increases above 2 mmols it is usually a sign the mitochondria are working at max capacity and can no longer re-use additional lactate as fuel. Working out above this intensity would not be sustainable indefinitely. See image below for professional cyclists vs amature cyclists vs metabolic syndrom patients. Amature cyclists (trains 3-5x a week) can average 175 watts under 2 mmols, sedentary population can barely maintain 100 watts and professional cyclists can output 275 watts! Most humans can’t maintain 275 watts for 2 min, and these athletes can maintain this for several hours, its impressive.
Clearance:
If one has a higher lactate clearance rate, one can perform better and also have higher lactate production per second and not be hindered as much. Lactate production vs. carb substrate is a good graph to show lactate clearance and efficiency. Lactate correlates with carbohydrates for fuel (glycolysis) however if CHO burn is increasing but lactate remains the same, the lactate shuttle system is superior and more efficient. As you can see below the professional athletes produce significant less amount of lactate per same amount of carbohydrate oxidation.
What does my Vo2 max say about my lactate threshold?
In short, not much! It is possible for two individuals to have similar Vo2 max scores with two different blood lactate levels. To put simply, ones Vo2 max allows us to see what your full potential is. Blood lactate will let us know how long you can work at certain intensities within your vo2 max. The typical Tour de France winner won’t have the highest Vo2 max on the circuit or even team. However, they can use the highest percentage of their max indefinitely. That’s because races are 4-6 hour stages with lots of climbing. If the races were shorter and on flat roads, the winners would be different. An example below shows how training can affect one’s sub max and max levels. Both tests ended around 10 mmols of lactate but post training the individual was able to sustain higher watts at lower lactate levels. Working longer and more intensely until lactate overwhelmed the system.
Lactate Testing for ZONING vs Power-Based Testing (FTP)
Right now, you may be wondering “Am I good at shuttling/Re-using lactate?” or “how accurate is my current training program”?
Power-based testing is common in cycling, whether this is testing FTP via a time-trial or ramp test, or testing power over a range of durations from 5 seconds to 20 minutes. While useful, these power-based tests have limitations when compared with lactate testing. The main issue being time. A 20 min test only means you can peddle at that output for 20 min. Someone with less peak power than you but can shuttle lactate better may have a similar 20 min FTP but will crush you on an hour long TT. This is where lactate testing is useful. Along with Vo2 calimatry which we provide as well!
1. Power is always generated by a combination of energy systems (Fat + Carbs)
This means that, if increases or decreases in power are seen, it’s not possible to tell which energy system is responsible, and thus what physiological changes have occurred.
For example, while the 1-minute test is often interpreted as representing anaerobic power, there is still a considerable contribution from the aerobic energy system. Thus, an improvement in 1-minute power could be due to an improvement in either the anaerobic or aerobic energy systems.
Likewise, the 20-min test is typically used to estimate FTP. However, an improved 20-min power could actually be due to an increased anaerobic power, which is great if you only ride for 20 min. But how much does that anaerobic power carry over to your 2-3 hour ride? Lactate testing can give us a better understanding of what processes are going on in the body at different intensities, and what changes are occurring over time, because lactate levels are closely linked to metabolic processes within the body.
2. Zones based on power testing are typically generalized
Using lactate testing can allow for training zones to be individualized based on the actual metabolic processes going on in the body.
Two of the largest markers for lactate testing are lactate threshold 1 and lactate threshold 2 or LT1 and LT2.
LT1 is usually when the body reaches levels of 2 mmols. This is the top end of your zone 2 (where majority% of your time training should be spent). Numbers will vary but a blood lactate of 1.5-1.8 will correlate with the highest absolute level of energy derived from fat.
Lactate threshold 2 or LT2 usually represents 4 mmols of lactate but can vary person to person. At this intensity little fat is being used and most energy is derived from carbohydrates. At LT2 lactate will start to increase 1 mmol every 10 min or so, this biomarker separates zone 3 and zone 4. One can exercise above their LT2 for 30-60 min.
