Lactic acid is a vital component for the proper working of the body. It increases in concentration during exercise but does not cause muscle soreness.
Lactic acid is integral to bodily function and is not solely a byproduct of exercise.
Some health conditions can increase lactic acid production or reduce the body’s ability to clear lactate from the blood. This can result in a more severe buildup of lactate, which doctors refer to as lactic acidosis.
In this article, we outline what lactic acid is, its role in the body, and the symptoms of lactic acidosis.
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The body uses lactic acid at a whole-body level. It plays an important role in the correct working of cells, tissues, and organs.
Lactic acid has three main uses in the body:
- as a major energy source for mitochondria
- as a precursor for producing glucose
- as a signaling molecule
Doctors previously thought that muscles produced lactic acid when low on oxygen. Research has shown this to be false. Lactic acid production is fully aerobic, meaning it occurs during normal respiration.
Neither lactic acid nor lactate are responsible for muscles soreness or burning sensations from exercise. In fact, lactic acid is an important fuel source for muscles during exercise, including those in the heart.
Muscle soreness after exercise occurs due to microdamage to muscles. It is not the result of lactic acid buildup in the muscles.
Muscle fatigue and burning during high intensity exercise result from an accumulation of intracellular metabolites such as inorganic phosphate and hydrogen ions that impair the contractile function of the muscle.
Intracellular metabolites are substances within cells that the body makes when it breaks down chemicals in a person’s system.
Lactic acidosis occurs when the body produces too much lactic acid and cannot process or remove it quickly enough. The condition can occur quickly and may lead to severe complications.
Lactic acidosis is often a complication of other health conditions. Some causes of lactic acidosis include:
Certain medications can also cause lactic acidosis. These include metformin, a first-line treatment for diabetes, and nucleoside reverse transcriptase inhibitors, which doctors prescribe to treat HIV.
Liver damage and liver disease impact the body’s ability to remove lactate from the blood. This can result in high blood lactate levels, known as hyperlactatemia. In some cases, hyperlactatemia can progress to lactic acidosis.
Heart failure, shock, and severe infections can reduce blood oxygen levels. This can increase the concentration of lactic acid in the blood, leading to lactic acidosis.
The symptoms doctors associate with lactic acidosis include:
Anyone who thinks they have lactic acidosis or hyperlactatemia should speak with a doctor immediately.
Diagnosis and treatment
A doctor will usually carry out a blood test to check levels of lactate in the blood. In some cases, they may ask the person not to eat, drink, or exercise for several hours before the test.
If the tests detect lactic acidosis, the doctor will work to diagnose and treat its underlying cause. Treatment will allow the body to dispose of the lactic acid in the usual way.
Lactic acid is an integral part of the human body. It assists in cell respiration, glucose production, and molecule signaling. Contrary to belief, lactic acid does not cause muscle soreness. However, the concentration of lactic acid in the blood does increase during exercise.
High levels of lactic acid in the blood can lead to hyperlactatemia and lactic acidosis. Specific health conditions can increase a person’s risk of developing hyperlactatemia and lactic acidosis.
Without treatment, both of these conditions can lead to severe, potentially fatal complications.
Lactic acid. Also know as the “burn” you feel on that last rep or final sprint, most athletes see it as a workout’s worst enemy, the cause of muscle soreness and fatigue. But what if everything you learned was wrong? Even at the highest levels of sport, misunderstandings about this natural compound occur. In the early stages of the Tour de France—after the race but before he donned the Yellow Jersey—Chris Froome was seen backstage pedaling on a trainer and cooling down. Former cyclists and stellar commentator Bob Roll explained that Froome was “getting the lactic acid” out of his legs so he would be less fatigued for the next day’s ride. Encapsulated in these comments are a whole bunch of misconceptions about lactic acid, fatigue and even recovery. It’s time we learn the truth and get to know the real lactic acid.
Lactic acid is gone in minutes
Lactic acid is made of two parts: the acid and the lactate molecule. Below is a slide from a classic study done in the late 1930s from the Harvard Fatigue Lab showing how fast lactic acid disappears from your blood (and muscles) after exercise. The units used in the 1930s are different from today’s measurements—10 mg% is equal to a modern value of about 1 millimoles/L. But the slide shows that after heavy exercise the lactic acid levels are back down to baseline within about an hour. It is true that it goes down faster with either walking or jogging, but it also goes down pretty fast if you do nothing. The other thing to remember that in events lasting hours, such as most stages of the Tour de France, it is unlikely that the muscle are producing a whole lot of lactic acid after four or five hours of cycling.
Lactic acid is not evil and your muscles are not anaerobic
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Over the last 30 or 40 years one of the world’s leading exercise scientists has been Dr. George Brooks at Cal. Dr. Brooks has led the way in showing a number of things, including that under most circumstances lactic acid is not caused by lack of oxygen, or “anaerobic” conditions, in exercising muscles. He and other colleagues have also shown that the lactate part of lactic acid can actually be a fuel for muscles and the heart and that the acid part of lactic acid is not the cause of fatigue. It might be a contributor, but fatigue is multi-dimensional and caused by a number of factors. Believe it or not, lactic acid is probably not causing the “burn” associated with intense exercise either. Here is a great summary by Dr. Bruce Gladden:
“For much of the 20th century, lactate was largely considered a dead-end waste product of glycolysis due to hypoxia, the primary cause of the O2 debt following exercise, a major cause of muscle fatigue, and a key factor in acidosis-induced tissue damage. Since the 1970s, a 'lactate revolution' has occurred…… It now appears that increased lactate production and concentration as a result of anoxia or dysoxia (hypoxia) are often the exception rather than the rule. Lactic acidosis is being re-evaluated as a factor in muscle fatigue….Lactate can no longer be considered the usual suspect for metabolic 'crimes', but is instead a central player in cellular, regional and whole body metabolism……”
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Lactic acid does not make you sore
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Back in the 1980s, a study was done to intentionally make people sore for 72 hours after exercise by having them run downhill, and that was how the authors answered the question, “Is Lactic acid related to delayed-onset muscle soreness?”
“Blood lactic acid concentration was measured before and during 45 minutes of treadmill running, one time on the level and once at a minus 10%(downhill) incline. Blood lactic acid concentration and subjective sensations of muscular soreness were assessed at intervals for 72 hours after the runs. Lactic acid concentration was significantly increased during running on the level, but subjects experienced no significant post exercise muscular soreness. Lactic acid was never elevated in downhill runners, but subjects experienced significant delayed-onset soreness. Results indicated that lactic acid is not related to exercise-induced delayed-onset muscle soreness.”
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So why was Froome cooling down?
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People routinely cool down or use other recovery techniques right after a race or hard workout, or in the days following one. As mentioned earlier, the causes of fatigue are multi-dimensional and perhaps cooling down does something that is just hard to measure scientifically in the lab. It is also possible that this is just sort of the custom and people do what works for them or what their coaches and trainers suggest. The biggest challenges in a long and brutal series of days like the Tour de France are avoiding dehydration and getting enough to eat and drink so the rider has plenty of carbs available. When you look for objective evidence that things like massage, compression and cold water work, you can’t always find a consistent story. Cold water or so-called contrast treatments seem to do help with perceptions of fatigue but not soreness. So it is a mixed bag with no magic bullet. Light exercise and NSAIDs like ibuprofen or naproxen can work, but the effects are temporary. In most cases recovery techniques might be summarized as if “it feels good then do it.”
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Stop the myth spreading
I started this piece with data that is now 80 years old that debunks one of the central myths about lactic acid and recovery after exercise. However, we hear the same old story about the evils of lactic acid, recovery and fatigue from commentators all the time. We are likely in for a big dose of “lactic acid is evil” during the Olympics and what Bob Roll said in passing during the Tour de France will be repeated hundreds of times in hundreds of languages. So when you hear it, please tweet to your favorite announcer and let them know there are some new old ideas about lactic acid out there.
Michael Joyner, is an expert in human performance at the Mayo Clinic, these views are his own. You can follow him on twitter @DrMJoyner.