The truth about lactic acid
Sometimes there are shortcuts or half-truths, or even outright errors, that end up being accepted as facts, simply because they have become part of popular belief and because they are simple, whereas reality is nuanced and complex. Thus, through laziness or ignorance, we contribute to spreading a lie.
This was the case long before the advent of social media, fake news spread by Russian intelligence agencies, and the election of a certain real estate mogul as leader of the most powerful country in the world.
When we came across an article by Dr. Jean-Pierre de Mondenard on the subject, we decided it was high time to put an end to one of the biggest misconceptions about lactic acid.
Much like websites that strive to debunk fake news or conspiracy myths, let's see what the science of physiology has to say when presented with some common misconceptions about muscle pain during exercise.
Statement: When your legs hurt during exercise, it is because your muscles are filling up with lactic acid.
Verification: This is false.
As Guy Thibault explains in detail, there is not just one type of fatigue, but several types of muscle fatigue. So even if we could blame lactic acid, it is highly unlikely that it is always and solely the culprit. As the doctor of exercise physiology suggests, pain during short bursts of effort—on the track, for example—and during an endurance race may be similar, but it is unlikely that they are caused by the same source.
Muscle fatigue is, in fact, multifactorial.
But regardless of the type of fatigue, lactic acid is NEVER the cause.
The problem is that the real explanations are complicated, which is probably why we always resort to this simplistic image of lactic acid buildup to explain this phenomenon.
It may also be because the burning sensation and heaviness are symptoms that naturally associate with the idea we have of the effect of acid, such as the feeling of having "full" and therefore heavy legs.
In reality, during exercise, this famous muscle lactic acid diffuses freely into the blood and initially breaks down, separating into a lactate ion and a hydrogen proton. It therefore cannot accumulate. Nor can it cause us pain.
Statement: In reality, it is lactate that is the waste product produced by exercise and causes pain.
Verification: Um, not really, no.
Without going into the full details of this highly complex process, let's just say that, on the contrary, lactate is largely used as an energy substrate by the muscles. It is therefore not a waste product. On the contrary, the oxidation of one mole of lactate releases 17 moles of ATP (the main fuel for muscles).
In fact, some studies show that cyclists perform better when their blood lactate levels are already high at the start of the race, hence the idea of warming up at high intensity before a sporting competition that requires peak performance right from the start. This is the case for time trials, cyclocross, and mountain biking, where the start of the race is as grueling as it is decisive.
Statement: The more lactate you produce, the more your legs will hurt the next day.
Verification: This is still incorrect.
After about 30 minutes of exercise, lactate production stabilizes depending on the intensity. In fact, we always produce lactate, and it is often our ability to generate more of it during exercise that explains our best athletic performances.
As for the pain the next day, i.e., muscle soreness, this is caused by inflammation of the muscles.
Toxins have nothing to do with it either.
As for pain during exercise, it can come from several sources.
Between the brain and the legs, the path traveled by various nerve impulses is as complex as it is far from being fully mapped. Similarly, the limits, thresholds, and other concepts accepted and used liberally by coaches are not necessarily all proven by science, Guy Thibault points out.
As Alex Hutchinson explains in his excellent essay Endure, it is probably the brain that is primarily responsible for the body's limits and tolerance thresholds.
There are also a multitude of subtleties in sports physiology that deserve closer attention and which, as studies have shown, enable athletes to sustain their efforts for longer periods of time.
For example, we know that ideal recovery, where the human body recycles lactate to feed the muscles, should be around 50-60% ofVO2 max . That's why training protocols often include periods of active recovery that involve more than just pedaling in the air, i.e., without any load.
But the more science delves into the question, the more new questions it unearths.
The truth, the whole truth about exercise pain and lactate management, is that we are only just beginning to understand them, and that repeated training is undoubtedly the best way to limit exercise pain.
In summary: you must accustom your body to handling exertion and pain, and your mind to enduring them...