Decades of research find lactate (or lactic acid) does not cause muscle soreness, rather, it is an essential part of glucose metabolism and energy production. But why do many clinicians and therapists believe otherwise?

The myths that massage therapy can help you get rid of lactic acid or lactate and that they are “toxins” are still prevalent among massage therapy culture. Among fitness and exercise professionals, this is also no exception since many trainers, coaches, and even exercise physiologists believe that lactate or lactic acid is a cause for muscle soreness due to the “burn” you get after a workout. Contrary to this popular belief, lactate actually reduces or buffers the rate of acidosis build-up and is not a contributor to acidosis and muscle soreness. (1)

Lactate is produced in all organs in your body, with your liver and kidneys being the top two producers when you are at rest. (2,3) During exercise, skeletal muscles are the largest manufacturers of lactate as a result of breaking down glucose for energy, especially during high-intensity, short-duration exercise like sprinting and Olympic lifting. When adenosine triphophate (ATP) is used for energy, it converts to adenosine diphosphate (ADP) with a released proton, which has a positive charge. When there is enough oxygen to meet muscle contraction demands, no proton is accumulated in excess within the cell since the extra protons in the cells’ cytosol get shuttled into the mitochondria. Through a series of chemical reactions, the mitochondria use the protons for oxidative phosphorylation, a complex process that involves enzymes oxidizing nutrients to produce a ton of ATP, (4) which allows us to compete and endure in marathons and Tour de France.

If exercise intensity increases to the point where the body relies more on glycolysis to produce energy, then protons accumulate in the cytosol which increases acidosis in the tissues. (5) Being a conjugate base, lactate (with a negative charge) comes in and scoops up the extra protons to slow down the acidosis increase. This allows you to continue to exercise a little longer. Otherwise, professional boxers would not last a three-minute round before their muscles refuse to contract, nor could you outrun an angry bear.

lactic acid lactate muscle soreness boxing

Glycolysis allows you to continue to produce ATP without oxygen, which allows you to sustain an extra minute or two during higher-intensity activities. Photo: Nicolas Celaya, https://www.flickr.com/photos/nikorimages/2860281484/#/

Some scientists argued that if lactate truly does cause acidosis, then the ATP processing within a cell should slow down acidosis by reducing lactate production during glucose metabolism. If such decrease occurs, the energy factory inside the mitochondria would also increase the rate of proton uptake from the lactate production by the mitochondria. However, experiments had demonstrated that decreasing lactate production decreases proton uptake, not increase. (1)

“…the best way to decrease metabolic acidosis is to decrease nonmitochondrial ATP turnover by stimulating mitochondrial respiration. For a given ATP demand, any effort to decrease lactate production without increasing mitochondrial respiration will worsen metabolic acidosis,” Robergs et al. (1)

Overall, lactate serves as a boundary between anaerobic and aerobic metabolism. It is a byproduct of glycolysis because the process does not require oxygen. When there is enough oxygen, lactate converts to pyruvate by donating two electrons (oxidation). Then pyruvate gets shuttled into the mitochondria and begins oxidative phosphorylation.

But how did the myth about lactate and muscle soreness start?

When we make an observation of a relationship between two events or data sets, we sometimes make a mistake by indicating one of these events causes the other to happen. In other words, we see trend A associates with trend B; and so, A causes B. This is the classic correlation versus causation problem where many journalists and even scientists make when they report.

correlation causation

Image: Tyler Vigen, Spurious Correlations http://www.tylervigen.com/spurious-correlations

Compared to other disciplines in biology, such as genetics and evolution, research in cellular metabolism—particularly among mammals—has not advanced much since the Roaring Twenties. The myth stems from more than 90 years of misinterpretation of observations of an increase of lactate associating with a drop of pH level in muscle and other tissues. One of the biggest critiques of the myth of lactic acid (or lactate) causes acidosis and muscle soreness is from a 2004 paper by exercise physiologists Robert Robergs, Farzaneh Ghiasvand, and Daryl Parker from the University of New Mexico. (1)

First, they said that the term “lactic acid” is a misnomer, since it was first discovered in sour milk (hence “lactic” referring to milk) by Swedish chemist Carl Wilhelm Scheele (1742-1786)  in 1780. They considered the name “trivial,” yet the term—along with “lactate”—got stuck in the chemistry and medical professions for the next three centuries. Because Scheele isolated the acid under “impure conditions,” many chemists in the early 19th century tried to find alternative explanations to his findings, such as the lactic acid is actually impure acetic acid. (1)

Despite the misnomer, Robergs et al. described two famous chemists, Otto Meyerhof and Archibald Hill, who gave an early understanding of how lactic acid works in relation to exercise in the 1920s. However, Robergs et al. highlighted that the knowledge base of acid-base chemistry and cellular respiration in the mitochondria were “insufficient” at the time, and the two chemists’ research did not directly experiment whether there was a cause-and-effect relationship between lactic acid/lactate and acidosis.

“…it is easy to comprehend how the Nobel prize quality of the work of Hill and [Meyerhof] was proof enough to the scientific world at that time for the interpretation that lactate production and acidosis were cause-and-effect,” Robergs et al. wrote. (1) Hill’s studies suggest that lactic acid is the “immediate energy donor for muscle contraction,” while Meyerhof showed that lactate is a byproduct of glycogen break down. (6)

Robergs et al. argued that much of the current medical education and research on lactate are still based on findings of Hill and Meyerhof’s time, which have not evolved, and the idea that lactic acid and lactate are the prime contributors to lactic acidosis still permeates in modern healthcare education. They suggested that the terms “lactate” and “lactic acid” should be “removed from any association with the cause of acidosis” in sports science, which can make coaches, trainers, athletes—and massage therapists—continue to spread the muscle soreness myth.

Like many health care myths, such as massaging a pregnant woman’s ankles can cause an abortion in her first trimester and “poor” posture is primary cause of back pain, the lactate and muscle soreness myth may have been passed down from generations of coaches, manual therapists, and athletes. The information spread so wide and far that even when a solid body of evidence indicates the opposite, the myth is already embedded into the culture—and it is very difficult to change people’s minds.

Massage therapists and other manual therapists can learn from the mistakes of this branch of human physiology by keeping ourselves updated and question what is learned in courses. Perhaps they can even help solve the problem by relaying up-to-date information their clients and patients.

“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.” ~ Bruce Gladden, Ph.D., Muscle Physiology Lab, Auburn University (6)

 

References

1. Robergs RA, Ghiasvand F, Parker D. Biochemistry of exercise-induced metabolic acidosis. 2004 Sep;287(3):R502-16.

2. Cano N. Beach-to-beside review: glucose production from the kidney. Crit Care (London, England) 2002;6:317-21.

3. Tayek JA, Katz J. Glucose production, recycling, Cori cycle, and gluconeogenesis in humans: relationship to serum cortisol. Am J Physiol 1997;272:E476-84.

4. Berg JM, Tymoczko JL, Stryer L. Biochemistry, 5th edition. New York: W H Freeman; 2002.

5. Chaudhry R, Varacallo M. Biochemistry, Glycolysis. [Updated 2019 Apr 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.

6. Gladden LB. Lactate metabolism: a new paradigm for the third millennium. J Physiol. 2004;558(Pt 1):5–30. doi:10.1113/jphysiol.2003.058701.

7. Ferguson BS, Rogatzki MJ, Goodwin ML, Kane DA, Rightmire Z, Gladden LB. Lactate metabolism: historical context, prior misinterpretations, and current understanding.  2018 Apr;118(4):691-728. doi: 10.1007/s00421-017-3795-6. Epub 2018 Jan 10.