For nearly 100 years, people have correctly associated lactic acid (or lactate) with exercise. However, the relationship between moderate to high intensity exercise with muscle fatigue and muscle soreness has resulted in the creation of lactic acid myths. In the absence of better information, like the lack of knowledge, it was easy to pin the blame on lactate, but now we know that lactic acid has received a bad rap. 

The soreness that we often get from exercise and sometimes after a massage is not caused by lactic acid buildup in muscles, nor is lactic acid responsible for post-exercise muscle spasms and delayed onset muscle soreness, muscle fatigue, or tight muscles

A lot of research published in the past 30 years has shown that each of these myths is, in fact, a myth. Lactate and lactic acid do not contribute these effects.

We know that these “exercise” symptoms are real, but they are due to other causes. These effects remain highly treatable with physical therapy and massage therapy.

What causes the muscle burn during exercise?

In simple chemistry terms, lactate is the dissociated form of lactic acid, in solution the cation and anions separate because of the properties of water. Lactic acid is composed of lactate anion and an associated proton (positively charged hydrogen ion, H+). 

In solutions like our body fluids, with pH between 6.2 (skeletal muscle with very high intensity exercise) and 7.5 (slight alkalosis), more than 98 percent of lactic acid is present in the form of lactate. 

Lactate is often mistaken for lactic acid, and they can be converted to each other during metabolism. (Illustration by Nick Ng)

Lactate is often mistaken for lactic acid, and they can be converted to each other during metabolism. (Illustration by Nick Ng)

 

These two forms are rapidly interchangeable in the body, and there is confusion in the use of these two terms because most people confuse the difference between lactate and lactic acid. When most people refer to lactic acid, they likely are referring to lactate.

Why do your muscles produce lactic acid?

Lactate is produced in most cells of the body using a biochemical pathway called glycolysis, the pathway responsible for the metabolic breakdown of glucose, either from glycogen stored in cells, such as in muscles and the liver, or from glucose transported into cells from the blood. 

Glycolysis is one of three main biochemical pathways used by muscles to produce the ATP (adenosine triphosphate) needed to support muscle contraction and relaxation during exercise, the other two pathways are phosphocreatine breakdown and mitochondrial respiration. 

While the mitochondria are the energy (ATP) powerhouses of muscle cells, the enzymes in the oxidative phosphorylation pathways are only slowly upregulated. The enzymes in glycolysis are always ‘on’ even at rest, but in contrast to the enzymes in the mitochondria are very rapidly upregulated when muscular activity occurs. 

When at rest, the concentration of lactate in muscles is about four times greater than that of blood. With 30 seconds of high-intensity exercise, muscle lactate concentration can more than double, and repeated bouts of high intensity exercise—with each bout lasting 10 seconds or longer—can result in muscle lactate concentrations approaching nearly eight times more than blood. 

Sporting activities with such repeated bouts include soccer, hockey, and football, where rest periods between bouts may be much less than 10 minutes. In contrast, heavy weightlifting, while intense, does not result in much, if any, muscle or blood lactate build up because the energy needed by muscles in short-lasting work is nearly completely supplied by phosphocreatine breakdown. In between reps, phosphocreatine recovery occurs rapidly (two to five minutes) mainly by increased mitochondrial respiration, not by glycolytic lactate production.

Increased muscular activity results in the breakdown of glucose with the production of ATP and lactate. Some of the lactate produced inside cells goes on into the mitochondria where it undergoes further metabolism (lactate oxidation) to produce more ATP via mitochondrial respiration. This is why endurance athletes can sustain their sport for a long period of time.

With moderate to high intensity exercise, lactate production can exceed the rate of how much the mitochondria can process and shuttle it away, which causes a buildup of lactate inside muscle cells and the release of lactate into the blood. This increases blood lactate concentration that is proportional to the duration and intensity of exercise.

How does your body “get rid” of lactic acid? 

Lactate is not a metabolic waste product or a “toxin,” even though this may seem to be the case because it’s released by contracting muscles during exercise. Rather, we know that lactate is used as fuel in the mitochondria of contracting and recovering muscle to generate ATP. 

We also know that lactate released into the blood from contracting muscle is taken up by other cells in the body including brain, liver, red blood cells, and non-contracting muscles. Lactate taken up by these cells is oxidized, (i.e. lactate is a valuable metabolic fuel that is not to be wasted). While some lactate is lost in the urine with very high intensity exercise, this is an exception. The body retains lactate and uses it. In fact, lactate is preferred over glucose as a fuel source, even in resting muscles.

Because of the mechanisms for lactate disposal in the body, lactate doesn’t persist very long after you stop exercising or cool down. Even with  very high intensity exercise lactate concentrations return to pre-exercise resting levels within 90 minutes.

Therefore, there’s no buildup of lactate in muscles—nor an elevated blood lactate concentration—in the hours and days after exercise when we may experience muscle pain and soreness, cramps, twitching, and muscle damage. For the most part, these ‘effects’ are the result of mechanical damage caused by the strength of muscular contractions and chemical damage caused by reactive oxygen species (ROS).

ROS are produced in the mitochondria of cells when mitochondrial respiration (oxidative phosphorylation) is elevated as occurs with moderate to high intensity exercise. They react with cell membranes, and other elements within cells, causing damage to the membrane and other structures including the contractile apparatus itself.

The amount of damage is proportional to the intensity and duration of exercise and is most notable in untrained muscle. The damaged muscle fibers leak molecules (i.e. creatine kinase (CK) into the extracellular fluids and blood). Some of the small cytokine molecules stimulate pain-sensitive nerve endings in muscle, causing the pain that is associated with intense exercise or with delayed onset muscle soreness.

Is there a supplement that helps reduce lactic acid? 

Sodium bicarbonate (bicarb) is the main supplement that has been used successfully to increase the rate at which muscles release lactate into the blood, thus reducing the buildup of lactate in muscle cells during exercise. The research also shows that bicarb supplementation supports the performance of short-duration (less than three minutes) high-intensity exercise. 

A recent systematic review of 189 research studies (2,019 subjects, mostly young adults, male and female athletes and non-athletes) reported that bicarb supplementation supports the performance of short-duration (less than three minutes) high-intensity exercise. When the analysis is performed using only female subjects, the same result of enhanced exercise capacity was obtained. 

While the systematic reviews do not comment on lactate, it is known that the blood alkalosis caused by bicarb supplementation enhances muscle lactate removal. This appears to be beneficial for contracting muscles, and lactate in the blood is rapidly taken up by most other cells of the body as metabolic fuel.

There are no supplements that are able to promote lactate loss after exercise because lactate is very easily and quickly disposed of by most cells of the body, which use lactate as metabolic fuel to produce ATP. Other supplements containing sodium citrate or other weak acid salts of sodium work in a way similar to that of bicarb. 

Check with your healthcare provider before you take any of said supplements. Do not substitute this for your medical advice.

Does massage therapy “release” lactic acid? 

Massage therapy does not get rid of lactic acid in a normal, post-exercise situation because there’s no persistent buildup of lactate. Massage, however, may be beneficial after you exercise to stimulate muscle blood flow perfusion (at rest the muscle fibers are only intermittently perfused), which helps with the healing and repair of damaged muscle fibers. 

In people with limb ischemia, such as may occur with peripheral artery disease, limb edema and vascular insufficiency there may be some buildup of lactate in muscle and other tissues. 

Massage therapy has much more benefits than “getting rid” of lactic acid, which is physiological implausible. It helps decrease stress and symptoms of depression and anxiety, particularly for cancer patients

Given what we know about lactic acid, glucose metabolism, and human touch, there’s no need to tell patients and clients that massage therapy can remove lactic acid or “toxins.”  Oftentimes, providing comfort, relaxation, and less pain is why they seek massage therapy.

dr michael lindinger
Michael Lindinger, PhD
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Dr. Mike Lindinger is a comparative animal physiologist and nutraceuticals specialist. He has been studying lactate metabolism in muscle, people and animals for 35 years. He received his training at the universities of Guelph, Victoria, McMaster, and Hannover and has worked with dozens of researchers on various physiology and nutraceutical research and development products.

He current serves industry and the public as President of the Nutraceutical Alliance, which helps people and companies develop functional and safe nutraceutical products for people and animals. He serves as an editorial board member for several human and veterinary science journals, and regularly presents science to the public in ways that non-scientists can understand.