Matteo Salvadorini - TriathlonCafe
For years, lactate has been seen as the enemy of athletic performance, associated with fatigue and muscle pain.
However, recent research in exercise physiology has completely reshaped this view, revealing that lactate is not just a byproduct of anaerobic metabolism but an essential fuel for both muscles and the brain. [1]
In this article, we will explore the role of lactate in energy production, how it is generated and cleared by the body, and how its measurement can become a key tool for optimizing performance.
First of all, a brief lesson in basic physiology:
Energy metabolism provides energy to our muscles through ATP. In fact, the goal of energy metabolism is to synthesize ATP.
ATP is a molecule composed of the sugar ribose, the nitrogenous base adenine, and three phosphate groups.
Without overcomplicating things, what is important to us are the bonds between phosphate groups.
These bonds can be broken to release energy from a reaction called hydrolysis when ATP reacts with H2O.
So, we understand that what we need to produce energy and so mechanical power is ATP, the energy metabolism can produce (or rather resynthesized) ATP in 3 ways:
- phosphagen system: where ATP is resynthesized almost immediately in the muscle by the phosphocreatine, a molecule composed of Creatine and a phosphate group.
This system is fast but depletes quickly due to limited stores of phosphocreatine (almost 15s) - Anaerobic Glycolysis: where ATP is resynthesized from glucose. The reaction underlying this process is: glucose (plus other substances) breaks down into 2 molecules of pyruvate + 2 ATP (plus other byproducts).
The pyruvate is sent to the mitochondria, if in excess, it is converted into lactate. - Aerobic System: is the “sequel” of the Anaerobic Glycolysis, in fact the pyruvate sent in the mitochondria, if in presence of oxygen, will be converted into Acetil-COA and enters the Krebs cycle.
The Krebs cycle produces a small amount of ATP along with NADH and FADH2, which are coenzymes used in oxidative phosphorylation to generate more ATP.
Note that Anaerobic System (Phosphagen system + Anaerobic Glycolysis) is essential to guarantee energy to the muscle during the activation phase of the aerobic system [fig3] or in order to produce more energy in case of maximal efforts, so when the demand cannot be fulfilled by only the aerobic system.
Under this condition, lactate builds up.
But Lactate is not just a metabolic byproduct; it plays a central role in energy metabolism. In fact, lactate itself is used as fuel: it can be reconverted into pyruvate in the muscles and enter the Krebs cycle, or it can be sent to the liver where gluconeogenesis takes place.
Rather than being just an alternative fuel, lactate serves as a preferred energy source during exercise because of its fast utilization and seamless integration with aerobic metabolism.
So, in a way lactate is preferred over glucose as an energy source! [1]
It's important to note that while an increase in intensity leads to muscle fatigue, this is not directly caused by lactate. [4]
Muscle fatigue is caused by acidosis. Every time ATP is broken down into ADP and Pi, a proton (H+) is released.
When exercise intensity increases, two things occur:
- Lactate buildup.
- An increase in ATP breakdown, which leads to a greater release of protons, resulting in acidosis.
Lactate production does not cause acidosis, instead it helps buffer the acidosis.
A small note: Lactic acid is NOT produced in the body because it is too acidic to exist in a physiological environment. Instead, lactate and a proton (H+) are produced directly. Lactate is the conjugate base of lactic acid and helps buffer acidosis.
The increase in lactate production coincides with cellular acidosis and remains a good indirect marker of metabolic conditions that induce acidosis.
If muscles didn’t produce lactate, acidosis and muscle fatigue would occur more quickly, severely impairing exercise performance.
Now that we understand the role of lactate in our energy metabolism, let’s dive into the kinetics of Lactate:
How does Lactate Build Up?
When we are in a steady state, meaning the effort is "easy" and the aerobic system meets all energy demands, lactate is still produced at a low level, which is referred to as the baseline.
When the intensity starts to increase, lactate builds up. This point is called LT1 (first lactate threshold). By convention, a deviation of 0.5 mmol/l from the baseline is considered.
When the intensity increases, we arrive at a point where the clearance of lactate is balanced with lactate production, meaning the rate of lactate removal from the bloodstream equals the rate at which it is produced. This results in a stable level of lactate in the blood.
This point is called LT2 (second lactate threshold) and it is around 4mmol/l but can vary significantly depending on the level of training. In order to precisely determine the lactate concentration, various tests can be conducted, one of which is the modified DMAX method [12] [13]. This is a complex method that we won’t see in this article, in addition, knowing the exac
TESTING PROTOCOLS
I would like to explain 2 protocols that I do often use to verify if the training is going to the right direction:
1. VLaMax (Maximum Lactate Accumulation Rate) is a measure that represents the body's ability to produce lactate during high-intensity exercise.
More specifically, it is the maximum amount of lactate an athlete can produce per unit of time during intense exercise, such as short, powerful efforts (typical of sprints or high-intensity efforts).
The higher the VLaMax, the greater the athlete's ability to generate power in short bursts of activity, which contributes to better acceleration.
The VLaMax test is usually used for sprinters or under 2-min race event.
Note that high VLaMax means also higher production of lactate even at low intensity, so this is a disadvantage for endurance athletes if too high.
Training Tips – You can increase VLaMax with sprint and power training, while decreasing it with endurance training.
VLaMax test protocol: [2]
- Measurement of BaseLine
- Max effort of 30s
- Lactate measurements every 1/2min for 10min after the effort in order to find the peak. The peak should occur after 6 minutes after the effort [9].
- (optional) Lactate measurement after 20min in order to see the clearance.
VLaMax [mmol/l/s] = (lactate peak – baseline) /23 seconds
Note that this is not an accurate measurement, in fact the protocol to measure VLaMax [3] is
where alactic = phosphagen system so to make it practical I choose 7 seconds.
But as always, we do not need to know precisely our VLaMax, we need to see the evolution of this value over the time in order to see if our training is going in the right direction.
In order to have same reference system: VLaMax goes from 0.1 (very oxidative and endurance athletes) to 1 (very glycolytic pure sprinters)
Note that through 30s of max effort we cannot reach our max lactate peak, so we can improve VLaMax by improving our lactate buffer, so reaching an higher lactate peak or by reaching the same lactate peak but faster.
2. GTX: In order to find LT1, LT2.
GTX (Gradient and Transition Exercise protocol) is a ramp incremental test used to assess metabolic performance. This test is the most used for endurance athletes.
The testing protocol which I’m going to discuss is the so called “visual LT” [14], it is the most empirical method, but it is also the most easy-to-use. In addition, it has been seen to be quite accurate.
Another interesting protocol is so-called LT4. This protocol implies that LT2 is at 4mmol/l.
A combination of this protocol is what I recommend, but first, the protocol:
The athlete will complete an incremental-intensity test, starting at easy effort and build up every 4-6min. The duration of the steps can depend on the type of athlete, for instance a glycolytic athlete will do only 4 min while an oxidative one will do 6min.
The recovery between sets can be from 30s up to 2/3min again in function of the type of the athlete and the length of the interval.
Lactate measurement will be after each step and recorded.
In [10] it has been seen that the max lactate peak after an effort occurred between 3 to 5 min after a short event but around 2 to 3 minutes after events that lasts at least 4 min.
LT1 will after an increase of around 0.5 mmol/l from the baseline AND when after the lactate still increases regularly. For instance, in some cases we can see, as in [fig6]
[1.4 – 1.9 - 1.7 - 1.9 – 2.3] mmol/l for [200 -220 -240 -260 -280] W
In this case, if we stop at the second measurement, we will say that LT1 stands at 220w, but this would be incorrect. In fact, if we proceed with the measurement, we can establish that LT1 stand at 260w cause after that measurement the lactate starts to build up.
Proceeding with the measurement we will step into LT2, we can see it because it will be around 4 mmol/l but especially after LT2 lactate start to increase more rapidly, for instance: [fig7]
[2.3 -2.7- 3.2 -3.8 -5.4] mmol/l for [280 -300 -320 -340 -360] W
As we can see at 340w we are around 4mmol/l and after that, for the same power interval increase, the increase in lactate will be bigger.
So, we know that our LT2 is around 340w.
[FIG6] [FIG7]
Note that this is a very empirical way to study lactate but is what is needed for practice and training.
As already mentioned, there are different ways to establish your precise LT1 and LT2 [12][13][14], complex and not very useful for training. Surely important for research, but for training not so much, because after 4 weeks of training your parameters will changes you have to start all over again, and also because our models of zones are identified as ranges, so for us it is important to know that LT2 is around 340w, s our Z4 will be from 320w to 360w!
Now let’s discuss how can I use these two protocols and why.
As I have already said maybe too many times, oour goal is to improve speed and reach the finish line as quickly as possible. Not just to achieve a higher LT2, etc... These are only instruments that we need to use to first evaluate our weaknesses, then to see if our training is going to the right direction.
This is interesting, but how can it be applied in practice?
Well it is not easy at all, It can differ a lot in function of the type of the athlete and the race but in order to do a general example I can say, either you are a short-distance (but still above 90s-2min events) or long-distance athlete:
If you lack endurance work with the second test-protocol and try to increase LT1 and LT2. For some sport is more important LT1, such as for cycling or long-course triathlon, for others LT2, such as running or short-course triathlon.
Repeat it after 8-12 weeks to see if your training plan is effective or needs adjustments.
If you lack in acceleration/power is a bit more complicated.
For instance, you can lack in velocity of build up or in lactic buffer. In both ways we will improve with HIIT training [11], but maybe in same cases power/strength training and/or sprint training is more useful. Either way you could you a VLaMax testing protocol in order to see improvements in this quality.
References
[1] BROOKS, George A. The science and translation of lactate shuttle theory. Cell metabolism, 2018, 27.4: 757-785.
[2] HARNISH, Christopher R.; SWENSEN, Thomas C.; KING, Deborah. Reliability of the 15-s Maximal Lactate Accumulation Rate (VLamax) Test for Cycling. Physiologia, 2023, 3.4: 542-551.
[3] PORTER, Michael; LANGLEY, Jamie. The relationship between muscle oxygen saturation kinetics and maximal blood lactate accumulation rate across varying sprint cycle durations. European Journal of Sport Science, 2025, 25.3: e12242.
[4] KEMP, Graham. Lactate accumulation, proton buffering, and pH change in ischemically exercising muscle. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2005.
[8] Davis, J.A., Rozenek, R., DeCicco, D.M., Carizzi, M.T. and Pham, P.H. (2007), Comparison of three methods for detection of the lactate threshold. Clinical Physiology and Functional Imaging, 27: 381-384.
[9] SHAHIDI, Seyed Houtan. The Temporal Dynamics of Blood Lactate Concentration and Oxygen Consumption Following Supra-Maximal Efforts. 2024.
[10] Gupta, S., A. Stanula, and A. Goswami, Peak blood lactate concentration and its arrival time following different track running events in under-20 male track athletes. International Journal of Sports Physiology and Performance, 2021. 16(11): p. 1625-1633.
[11] EDGE, Johann; BISHOP, David; GOODMAN, Carmel. The effects of training intensity on muscle buffer capacity in females. European journal of applied physiology, 2006, 96.1: 97-105.
[12] CHENG, B., et al. A new approach for the determination of ventilatory and lactate thresholds. International journal of sports medicine, 1992, 13.07: 518-522.
[13] CZUBA, Miłosz, et al. Lactate threshold (D-max method) and maximal lactate steady state in cyclists. Journal of Human Kinetics, 2009, 21.1: 49-56.
[14] MCGEHEE, James C.; TANNER, Charles J.; HOUMARD, Joseph A. ACOMPARISON OF METHODS FOR ESTIMATING THE LACTATE THRESHOLD. The Journal of Strength & Conditioning Research, 2005, 19.3: 553-558.