Lactic Acid, Lactate and Threshold Sessions Part 2/2

Lactate isn't just an "acid warning," it's also a portable fuel that the body can use smartly. If you haven't read the first article in the series, start with part 1 here. In this part, we move from theory to practice: what different threshold concepts mean, why test methods like lactate threshold and maximal steady state might be more useful than just maximum oxygen uptake (VO₂max), and how you can think about measurement, recovery, and structuring of threshold sessions. The conclusion: choose a concept and a method you can measure consistently over time, and use it to guide training, not to chase the "right" number.

Measuring lactate in various ways can often be a more practical tool for performance management than VO₂max. If you can measure both VO₂max and your lactate threshold, maximal lactate steady state (MLSS), or when lactate begins to accumulate in the blood (OBLA), these two measurement tools are together really great for ensuring your training is actually yielding results. (Adv.Exc.Phys 2ed.s388).

As we mentioned in the first article, lactate is a mobile energy substrate formed when lactic acid breaks down into lactate and free hydrogen ions. The hydrogen ions lower the acidity (pH) in the muscles and are the most likely cause of muscle fatigue and that famous “burn” you feel in the muscles when intensity is high.

The lactate threshold (LT) or anaerobic threshold (AnT) are essentially the same and occur simultaneously according to many descriptions. LT is the point when oxygen becomes inadequate for the workload, and we begin to operate more anaerobically. At this stage, lactate in the blood starts accumulating more rapidly than it can be removed. Different terms and abbreviations often get mixed up in the literature— the aerobic threshold might be referred to as AT or VT, and the anaerobic threshold may also be abbreviated as AT in some sources (which can be confusing). Some researchers mention the "first" and "second" lactate threshold. In this article, we consistently use VT for the ventilatory/aerobic threshold and LT for the lactate threshold/anaerobic threshold.

OBLA is a fixed level at 4.0 mmol (millimoles per liter) lactate in the blood. Whether OBLA is a good measure for sports and performance development is controversial. Some researchers argue that OBLA represents a fixed point where our muscles do not get the oxygen needed to continue developing the same work. Others, as we pointed out in the previous article, argue that lactate in the bloodstream does not necessarily reflect the amount of lactate in the muscle, because the muscle itself uses lactate as fuel and because lactate in the blood can come from several different muscles while the limiting muscle may have reached its oxygen limit earlier during the test.

If you're on a trainer at home doing eight-minute threshold intervals, you can get localized acidosis in the thighs after, say, five minutes. Let's say we have 6 mmol lactate locally in the thigh muscles at that point. In the blood, you could simultaneously have only 2.5 mmol lactate if you are efficient at clearing the lactate from the bloodstream and moving it to other muscles that need the energy. The point is that 4 mmol in the blood (OBLA) does not give an exact local indication of how well you are working anaerobically in a specific muscle. Therefore, OBLA must be measured in the specific discipline where you want to know your OBLA. If you are a cyclist, a cycling test applies; if you're a triathlete, both cycling and running tests apply if you want to use OBLA as a tool.

MLSS stands for Maximal Lactate Steady State, representing the highest lactate level you can sustain over time without it increasing by more than 1 mmol/L during the test period. Typically, MLSS is assessed through a series of 30-minute submaximal tests. A protocol from a study examining various sports revealed that participants first completed max tests (Maxwatt) in their respective sport (rowing, speed skating, and cycling). This was followed by a set of 30-minute submaximal tests, with lactate levels at MLSS recorded at 3.1 (rowing), 5.4 (cycling), and 6.6 mmol/L (skating). These were the levels they could maintain steadily over the 30 minutes without a sudden increase. Differences in lactate at MLSS likely depend on the working muscle mass during different tests. The intensity they could sustain as a percentage ranged from 72–78% of Maxwatt, marking where their MLSS was, and this intensity can serve as a useful guideline.

As highlighted above, MLSS is not a constant value and has been documented in various studies to range from about 2–8 mmol in the blood. MLSS is NOT necessarily a level to sustain in shorter competitions, as you often want the lactate level to rise gradually so that just before the finish line, you're over the threshold and fully exerted as you finish. However, if you are running ultramarathons or participating in full-distance triathlons, MLSS might be a good level to monitor. 

In practice, MLSS is often compared to FTP (Functional Threshold Power), which is a more everyday tool focused on power output instead of lactate levels. FTP essentially refers to the level of effort you can maintain for about an hour, making it a time-based proxy for MLSS.

In cycling studies, MLSS has been reported around 201 W in one study, approximately 3 W/kg (~235 W for a certain body weight) in another [2], and 199 W in a third [3]. However, there's a range from about 100–300 W among people who train between 0 to over 20 hours per week.

Whether you have a high or low lactate level at your MLSS has no direct correlation to your performance. Hence, a high and stable lactate level in the blood (i.e., MLSS) is not necessarily better than a lower level. Two people may differ in their ability to metabolize lactate locally in the muscles, so the level in the blood doesn't always reflect actual performance.

What you want to improve when training to boost your MLSS is the speed or power you can sustain over a given time without the lactate suddenly spiking. MLSS testing requires multiple tests, takes time, and can be costly to conduct. Therefore, many testing centers use OBLA to estimate your MLSS. TrainingPeaks also has its own widely-used calculation for MLSS, which they call FTP.

Technology is always Awesome—ever since we learned to tame fire, make knives, and those old 286 computers (for those who remember them). Now, more and more non-invasive techniques are developing to measure various metabolites in the body. You've surely seen optical heart rate monitors that measure pulse via light, or clips that measure oxygen saturation via the finger—same basic principle.

Now, there are also tools that measure lactate, hydrogen ions, and salts in sweat or in the fluid just under the skin using optical measurement, which can provide us with much more data and enable better individualized training and nutrition. Take a look, for example, at BSX's lactate meter reviewed by DC Rainmaker. It has also been tested by independent researchers and has proven to be reliable among both males and women aged 18–45 during running. The discrepancy compared to blood tests in the study was 1.3–9.4%, but regarding test–test reliability, it showed consistent deviations. As long as a device shows the same "error rate" over time, it can still be a valuable tool for measuring progress.

While lactate itself isn't harmful, there's a nearly linear relationship between lactate levels in the blood and training intensity. Consequently, there's a corresponding connection between lactate and recovery. Research indicates that the optimal exertion level for quick recovery after a challenging threshold session is around 30–45% of VO2max for cycling, and 55–60% of VO2max for running.

Exercising at about 60% of maximum heart rate (approximately 40% of VO2max) for 30–40 minutes appears to facilitate the fastest recovery. In one study, researchers also tested a strategy involving 7 minutes of active rest at 65% of VO2max (at or just below the threshold) followed by 33 minutes at 35% of VO2max. However, this wasn't more effective than simply doing 40 minutes at 35% of VO2max (Exercise.Phys 7ed.s175). The reason active recovery is superior to passive recovery is that sustained increased blood flow helps remove metabolites more quickly.

Now let's try to summarize everything in a nice bullet list:

• Ventilatory threshold – Where your lactate levels start to rise above resting values and your workout becomes noticeably demanding. This occurs even though there is still plenty of oxygen available.
• Lactate threshold / Anaerobic threshold – Where the intensity is so high that the oxygen is insufficient and the removal of lactate in the blood can't keep up. The levels increase continuously from here.
• MLSS is the level where you have the highest lactate possible over time without it increasing more than 1 mmol/L. Your MLSS is often around 72–78% of maximum workload, which often corresponds to your FTP. The usual level is around 4 mmol, but it can vary between approximately 2–8 mmol between different individuals. OBLA is therefore not a 100% consistent measurement tool but works for many.
• OBLA is when your lactate levels in the blood are 4.0 mmol. Some researchers argue that this fixed value reflects the limit where muscles can no longer continue working at the same intensity.
• Your threshold sessions, aimed at training to handle and accumulate lactate, should have a working time of 20–60 minutes. So 40 minutes is a good average.
• Since lactate is a mobile fuel, as a triathlete, you can fatigue the upper body at the end of the swim and thus create lactate that can then be used in the legs during the cycling segment, when the blood flow is directed to where you start pedaling.
• For the fastest recovery after threshold sessions, 30–40 minutes of active rest around 60% of max heart rate is recommended, i.e., zone 1–2. Plan some low-intensity volume training after tougher sessions.

Do you want help interpreting your own lactate values or setting up threshold sessions according to your goals? Feel free to ask — we love geeking out on numbers and getting you to perform more, with a smile (and maybe some burning thigh muscles).