Lactic acid was once believed to be the cause of sore muscles after exercise. It’s not. Another substance, lactate, contributes. However, what causes muscle burn and pain is more complex. Staying hydrated and resting muscles may help.
If you participate in high intensity interval training or similar intense exercise, you’ve probably felt the intense burn in your muscles that often comes with this type of activity.
This burning sensation is frequently attributed to lactic acid buildup. For years, recreational and competitive athletes have assumed that, in order to increase performance, they have to minimize lactic acid in their bodies. However, this notion is false.
That’s right: Lactic acid is not the cause of the burn during intense exercise, nor is it responsible for the persistent soreness that may last from hours to days following intense exercise.
What’s more, exercise physiologists are continuing to study the complexities of what we’ve traditionally called “lactic acid buildup.” As it turns out, this term is a misnomer, because the metabolic byproduct of intense exercise is actually lactate.
Nevertheless, lactic acid and its associated molecule lactate are key compounds that play a role in metabolism, especially during intense exercise. Understanding their role in your fitness will help you perform better in your chosen athletic pursuits.
This article breaks down everything you need to know about lactate, lactic acid, and exercise, including what they do, how they’re produced, and whether it’s necessary or possible to get rid of lactic acid.
The answer, in short, is no.
Muscle burn and fatigue was traditionally attributed to lactic acidosis, which was thought to be the overabundance of lactic acid building up in the muscles when oxygen was low, such as during intense bouts of heavy exercise.
Researchers have since discovered that lactic acid doesn’t actually exist in our bodies, because our blood pH level is too high (1).
Instead, within metabolic processes, the lactic acid molecule is separated into two parts: lactate and a singular hydrogen ion (also known as a proton) (2).
Lactic acid vs. lactate
The terms “lactic acid” and “lactate” are often used interchangeably, but they are not technically the same.
Lactic acid is a combination of a negative lactate ion and a positive hydrogen ion.
When lactic acid is dissolved in water, which is virtually always the case in the human body, the ions split into a lactate ion and a hydrogen ion. Therefore, it’s more accurate to say that lactate — not lactic acid — is the byproduct of exercise.
Lactic acid was commonly thought of as the culprit for muscle soreness, fatigue, and loss of performance. However, research has shown that this is not the case.
Without getting too deep into biochemistry and physiology, it’s easiest to understand this way: Your body fuels your muscles through a process called glycolysis, in which it breaks down glucose (from the foods you eat) and produces adenosine triphosphate (ATP) (
ATP is what your muscle cells use as fuel. But the amount of ATP generated from glycolysis depends on whether oxygen is present during glycolysis (4,
When you exercise at high intensities, your body increasingly relies on fast-twitch muscle fibers to generate power. But these fibers in particular don’t have the capacity to use oxygen as efficiently (
So, in a heavy workout — like when you’re lifting heavy weights or pushing your cardio limits — the demand for ATP is high, but oxygen levels are low.
When that happens, glycolysis becomes anaerobic. In anaerobic glycolysis, the end product of glucose breakdown is lactate. This results in higher levels of circulating lactate in the bloodstream.
Additionally, researchers have found that lactate is produced more frequently than we thought — even in aerobic conditions (
Lactate is produced normally by certain cells and is a byproduct of anaerobic glucose metabolism, but it can also be produced in aerobic conditions.
Traditionally, lactic acid has gotten a bad rap as the reason our muscles burn and fatigue during exercise. But to recap: The byproduct of metabolic processes is lactate, not lactic acid… and those stubborn hydrogen ions, which we’ll get to in a moment.
Lactate is a biomarker of fatigue and glucose breakdown, but it’s not actually the cause of muscle fatigue (8).
In fact, lactate plays an important role in cellular processes, with some organs, such as the brain and heart, using it as a preferred energy source (
Your liver and kidneys can also convert lactate into glucose through a process called gluconeogenesis, allowing your body to use the glucose for energy (
So the bad reputation that lactate (or what we thought was lactic acid) gained over the years was unfounded.
The burn you feel when you’ve maxed out your performance is a result of the circulating hydrogen ions left over in your cells, which create an acidic environment, along with phosphates — additional byproducts of muscular metabolism (
Increased lactate buildup goes hand-in-hand with a drop in cell pH that occurs as a result of the hydrogen ion separating from lactic acid. This hydrogen ion is responsible for the muscle burn we often feel.
Although the drop in cellular pH results in the temporary burn during intense sets, lactic acid is not responsible for the delayed onset muscle soreness (DOMS) that often follows intense exercise.
DOMS is a complicated topic, and researchers continue to uncover insights about possible mechanisms.
The most commonly accepted theory is that DOMS likely occurs as a result of a combination of localized micro damage to muscle fibers and inflammation, which are beyond the scope of this article (15).
The main takeaway is that neither lactic acid nor lactate ions are responsible for the soreness you feel 12–72 hours after a workout.
Neither lactic acid nor lactate causes muscle soreness.
The lactate threshold is the point at which your body cannot clear lactate at the rate it’s producing it. This is when lactate begins to accumulate in your blood. This can occur as a result of increased lactate production or decreased lactate clearance.
During exercise, lactate levels rise, and lactate is recycled to fuel other cells and processes in your body.
Oxygen is required to metabolize lactate. But when your exercise reaches an intensity beyond what your aerobic system can handle, lactate accumulates in your blood (16).
Once you reach your lactate threshold, your body is producing lactate and releasing hydrogen ions in excess, which results in a drop in pH and a more acidic environment in your muscle cells, causing that burn.
This will continue until your oxygen intake increases enough to match the demand on your muscles.
For example, doing intervals of squats with medium weight for 10–15 reps is likely to result in a pH-related burn in your lower body. This burn is a direct result of your body metabolizing glucose faster than it can supply oxygen.
At that point you breathe more heavily and may feel short of breath as your body tries to increase oxygen intake. You may stop exerting yourself and notice that the burn dissipates as the cellular pH rises and the acute fatigue in your muscles begins fading.
Lactate buildup that occurs as a result of reduced lactate clearance is a more serious problem.
Decreased liver and kidney function are primarily responsible for decreased ability to process lactate. This loss of function can occur for a variety of reasons, not limited to (
- medications (acetaminophen, metformin, salycylates)
- alcohol consumption
- other liver and kidney disease (for example, cirrhosis)
The lactate threshold is the point at which your body is producing more lactate than it can clear. Oxygen is required to help clear lactate and bring the muscle cells back to a more balanced pH.
Lactic acidosis is a dangerous condition caused by lactate buildup in the blood exceeding 4mmol/L. In a diseased state, lactate levels in the blood are much higher, which could be due to limited blood flow to certain tissues or other problems (
As such, elevated blood lactate levels are often an indication of disease (18).
Even moderately elevated levels of lactate that occur as a result of poor lactate processing can be very harmful. Higher all-cause mortality is associated with elevated lactate levels between 2mmol/L and 4mmol/L, referred to as hyperlactatemia (18).
While temporary hyperlactatemia can be exercise-induced, harmful lactic acidosis is unlikely to occur as a result of intense exercise in people with normal kidney and liver function.
Lactic acidosis is an extreme buildup of lactate that can occur when kidney and liver function are impaired. It can also occur temporarily during intense exercise.
Your body naturally processes lactate in your liver and kidneys.
As mentioned, high intensity exercise that exceeds your body’s aerobic capacity will cause lactate to build up.
When you stop exercising or reduce your exercise intensity, your body will continue clearing the lactate, which typically dissipates the burn and fatigue caused by pH drop.
If you’re generally healthy, there’s no need to get rid of lactate by doing anything special. Your body has a well-tuned mechanism for processing lactate.
Basic health advice such as staying hydrated during exercise will help keep your body functioning optimally.
During recovery periods such as between sets, or even during your set, taking deep breaths can increase the oxygen delivery to your blood, potentially increasing lactate clearance.
Finally, stopping exercise and allowing lactate to clear is the surefire way to get rid of excess lactate.
Your body naturally gets rid of lactic acid through metabolism. Taking deep breaths, staying hydrated, and reducing exercise intensity are the best ways to maximize natural lactate clearance.
While there’s no secret to getting rid of lactate, it is possible to increase your lactate threshold.
No matter how fit you are, if you exceed your lactate threshold, the clock immediately begins ticking on how long you can sustain that effort. Conversely, exercising below the lactate threshold allows you to sustain energy for a very long time.
You can train your body to perform at a higher intensity without the buildup of lactate and increase your lactate threshold. However, this requires you to improve the efficiency of your aerobic system.
While this is not technically “preventing” the buildup of lactate, it does mean that you can run faster and longer before you reach the point of that muscle burn.
In fact, the goal of aerobic training for competitive and performance purposes revolves around increasing your lactate threshold.
For example, a competitive runner maintaining a 6-minute mile pace over multiple miles will be primarily using the aerobic system.
A less conditioned person may run the same 6-minute mile pace, but because their aerobic system is not as efficient and trained, they will rely on anaerobic energy to maintain the pace, which results in increased lactate and burn and fatigue due to metabolite buildup.
If this second person continually trains at or near their current lactate threshold, they may eventually be able to run at a 6-minute mile pace without using anaerobic energy, and this will eliminate the associated lactate buildup.
Regardless, once you hit your lactate threshold, you are subject to all the effects associated with lactate buildup and there’s little you can do other than take a rest and breathe deeply.
You cannot completely eliminate lactate buildup during anaerobic exercise, but you can improve your lactate threshold by increasing the intensity at which your workout becomes anaerobic.
Lactate is an important component of energy metabolism. Although it has historically been blamed for muscle soreness, it’s not responsible for this effect and is, in fact, a fuel for many organs of your body.
However, lactate does occur as a byproduct of intense exercise, and the buildup of hydrogen ions that occurs when it’s produced is thought to be responsible for the fatigue and burn you feel during this type of activity.
Your body has a natural process for clearing lactate that relies on proper kidney and liver function and oxygen. There’s not much you can do beyond keeping yourself healthy and hydrated to increase your baseline lactate metabolism.
Blood lactate increases caused by metabolic dysfunction are another story altogether. If these occur, you should address them with a healthcare professional.
Through exercise training, you can improve your lactate threshold, which will mean you can work out harder or run faster before you reach the point at which lactate starts building up and your muscles become fatigued.
With that in mind, do not overly concern yourself with lactate or lactic acid. If you’re still sore days after your workout, consider remedies appropriate for DOMS.
In the meantime, train hard, drink water, and embrace the burn.