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Lactic acid vs lactate: why are muscles sore after working out?

Lactic acid build up has had a bad reputation, but is that really why muscles are sore after working out? What about lactate threshold?

For a long time, it was believed that lactic acid build up was the cause of muscle soreness and that it had to be minimized to increase performance. Turns out that was wrong. Let’s take a closer look at what lactic acid actually is and what it means for your own fitness practice.

Is lactic acid causing you “muscle burn”?

With high intensity exercise, you’ve likely experienced an intense burn feeling in your muscles. Sometimes we even take pride in that “feel the burn” sensation!

Contrary to popular belief, muscle burn isn’t a result of lactic acid build up. Neither is it the cause of post-exercise soreness that can last a few hours to a few days.

Although muscle fatigue is typically attributed to lactic acidosis, or an excess buildup of lactic acid in the muscles, this is false. Studies have now shown that lactic acid can’t be produced in our body, as our blood pH level is too high.[1]Robergs RA, McNulty CR, Minett GM, Holland J, Trajano G. Lactate, not Lactic Acid, is Produced by Cellular Cytosolic Energy Catabolism. Physiology. 2018;33(1):10-12. doi:10.1152/physiol.00033.2017
Actually, lactic acid molecules are divided into two during the metabolic process. The result is a singular hydrogen ion (or proton) and lactate.[2]Sun S, Li H, Chen J, Qian Q. Lactic Acid: No Longer an Inert and End-Product of Glycolysis. Physiology. 2017;32(6):453-463. doi:10.1152/physiol.00016.2017

Lactic acid vs lactate

Even though lactic acid and lactate are used interchangeably in the fitness community, technically they are two different things.

Lactic acid is composed of a negative lactate ion and a positive hydrogen ion. In the body, lactic acid dissolves itself because of water. The ions then split into a lactate and hydrogen. Hence, it’s not lactic acid but lactate that is the byproduct of physical activity.
In fact, lactate is a source of fuel for the body and helps its functioning.[3]Brooks GA. Lactate as a fulcrum of metabolism. Redox Biol. 2020;35:101454. doi:10.1016/j.redox.2020.101454 While we exercise, lactate supports our muscle cells’ anaerobic energy production for up to three minutes, enabling us to operate at high levels.

Why does our body produce lactate?

Keeping things simple, our body fuels our muscles via a process called glycolysis. Basically using the food we eat, the body breaks down glucose to make adenosine triphosphate (ATP).[4]Naifeh J, Dimri M, Varacallo M. Biochemistry, Aerobic Glycolysis. StatPearls. Treasure Island (FL): StatPearls Publishing; August 10, 2021.

ATP is what our muscle cells use as fuel. Yet the quantity of ATP from glycolysis is contingent on the amount of oxygen present during the process.[5]Rowe I, Chiaravalli M, Boletta A. ATP and Lactate Quantification. BIO-PROTOCOL. 2013;3(23). doi:10.21769/bioprotoc.986 [6]Chaudhry R, Varacallo M. Biochemistry, Glycolysis. StatPearls. Treasure Island (FL): StatPearls Publishing; August 10, 2021.

However, with high intensity exercise, our body relies more on fast-twitch muscle fibers. Yet, these specific fibers aren’t efficient in using oxygen.[7]Mishra P, Varuzhanyan G, Pham AH, Chan DC. Mitochondrial Dynamics is a Distinguishing Feature of Skeletal Muscle Fiber Types and Regulates Organellar Compartmentalization. Cell Metab. … Continue reading

So basically, during a high intensity exercise session, there’s a high demand for ATP but oxygen levels are low. As a result, glycolysis becomes anaerobic. Finally, it’s with anaerobic glycolysis that glucose gets broken down into lactate, resulting in higher levels of lactate in the bloodstream.

Noteworthy, new studies are finding that lactate is also produced in aerobic conditions.[8]Brooks GA. The Science and Translation of Lactate Shuttle Theory. Cell Metabolism. 2018;27(4):757-785. doi:10.1016/j.cmet.2018.03.008 This might bring new understandings about our metabolism in the near future.

Related: Can you skip warming up before working out?

So why are muscles sore after working out?

Since lactic acid isn’t the culprit for our sore muscles, is it lactate then? Well lactate is a biomarker of fatigue and glucose breakdown. Yet, it’s not the actual cause of muscle fatigue. [9]Todd JJ. Lactate: valuable for physical performance and maintenance of brain function during exercise. Bioscience Horizons. 2014;7(0):hzu001-hzu001. doi:10.1093/biohorizons/hzu001

Lactate is in fact an important element of physical performance. It is an important energy source for organs like the brain and the heart during exercise.[10]Brooks GA. The Science and Translation of Lactate Shuttle Theory. Cell Metabolism. 2018;27(4):757-785. doi:10.1016/j.cmet.2018.03.008

When you feel muscle burn and fatigue, it’s actually a result of the hydrogen ions circulating in your body, resulting in an acidic environment and soreness.[11]Burger, M. Schaller DJ. Metabolic Acidosis. StatPearls. Treasure Island (FL): StatPearls Publishing; August 10, 2021.

Bottom line, neither lactic acid nor lactate are responsible for the “burn” we feel after an intense exercise bout.

It’s a topic of interest for researchers, but we don’t have a clear explanation for muscle soreness yet. A possible theory is that micro-tears to muscle fibers and localized inflammation are responsible for delayed muscle soreness.[12]Sonkodi B, Berkes I, Koltai E. Have We Looked in the Wrong Direction for More Than 100 Years? Delayed Onset Muscle Soreness Is, in Fact, Neural Microdamage Rather Than Muscle … Continue reading

Related: 13 health benefits of ginger. Check out #11! Ginger to relieve joint and muscle pain

What about lactate threshold?

Lactate threshold is the level at which your body can’t clear as much lactate as it is producing. It’s at that point that lactate starts accumulating in your blood.

It’s not something to worry about in itself. As lactate levels increase, it is used as fuel for other cells and processes in our body.

To metabolize lactate, our body needs oxygen. But when your exertion intensity is above what your aerobic system can handle, lactate increases in your blood.[13]Hall MM, Rajasekaran S, Thomsen TW, Peterson AR. Lactate: Friend or Foe. PM&R. 2016;8(3S):S8-S15. doi:10.1016/j.pmrj.2015.10.018

When you’re at your lactate threshold, your body is generating lactate and letting go hydrogen ions in excess, which leads to a drop in pH and a more acidic environment in your muscle cells, resulting in that burn.

This process goes on until your oxygen intake is able to match your muscles’ demand.

Feeling the lactate threshold

In context, when you’re doing bicep curl reps with dumbbells, after a number of reps, you will start feeling muscle exhaustion and that special burn feeling. That’s a sign that the pH in your arms has dropped and that your body is metabolizing glucose at a higher rate than it can supply oxygen.

At the same time, you start to breathe more heavily and might even feel short of breath because your body is trying to increase oxygen supply. As you stop the exercise, you can notice that the burn dissipates on its own, as the muscle’s acidity level starts getting back to normal and the fatigue is right away less noticeable.

When lactate buildup can be an issue

If you’re healthy, your body gets rid of lactate naturally and easily. It’s not something you need to worry about. However, if your body is having issues clearing lactate accumulation in your bloodstream, that can actually be cause for concern.

When the liver and kidney are dysfunctional, our system is limited in its ability to get rid of lactate. Some of the roots of this impairment can include medications (such as acetaminophen, metformin, salicylates), alcohol consumption, and other liver and kidney disease. [14]Foucher CD, Tubben RE. Lactic Acidosis. StatPearls. Treasure Island (FL): StatPearls Publishing; July 19, 2021.

What is lactic acidosis?

Lactic acidosis is a serious condition due to lactate buildup in the blood above 4mmol/L. In a diseased case, lactate levels in the blood are much higher. This can be the result of limited blood flow to certain tissues or an indication of other sickness.[15]Andersen LW, Mackenhauer J, Roberts JC, Berg KM, Cocchi MN, Donnino MW. Etiology and therapeutic approach to elevated lactate levels. Mayo Clin Proc. 2013;88(10):1127-1140. … Continue reading[16]Vincent, JL., Quintairos e Silva, A., Couto, L. et al. The value of blood lactate kinetics in critically ill patients: a systematic review. Crit Care 20, 257 (2016). … Continue reading

Even somewhat high levels of lactate caused by poor lactate processing can be dangerously harmful. Higher all-cause mortality is linked to elevated lactate levels between 2mmol/L and 4mmol/L, called hyperlactatemia.[17]Vincent, JL., Quintairos e Silva, A., Couto, L. et al. The value of blood lactate kinetics in critically ill patients: a systematic review. Crit Care 20, 257 (2016). … Continue reading

Although momentary hyperlactatemia can be due to exercise, serious lactic acidosis is not to be feared for people with healthy kidney and liver function.

Should you try to get rid of lactate?

It’s a natural mechanism for our body to clean up lactate in our liver and kidneys. When we perform at our threshold, our body’s aerobic capacity induces lactate to accumulate in our blood stream. For our system, clearing that up is part of post high intensity exercise recovery.

Once we finish our session or reduce our intensity, our body starts clearing the lactate. Right away, we can feel the fatigue and burn dissipate as the pH returns to normal.

There’s nothing you need to do to reduce lactate post workout. If you’re relatively healthy, your body processes lactate efficiently.

Nonetheless, supporting your body’s functioning during your training is a good idea. Keep well hydrated and make sure you breathe properly to get enough oxygen to your cells.

Increasing lactate threshold can help your performance

Although there’s no issue with having a high level of lactate in your body when you are healthy, it can be helpful to increase your lactate threshold.

Independent of how in shape you are, you have your own lactate threshold. Once you have exceeded your lactate threshold, it becomes increasingly difficult to maintain your exertion. On the contrary, sustaining your effort below your lactate threshold lets you maintain your performance much longer.

To increase your lactate threshold you need to improve your aerobic system’s efficiency. In a few words, this can be done by training near or at your current limit. Overtime, this can increase your lactic threshold.

Key takeaway

  • After a high intensity workout, lactic acid and lactate aren’t to blame for our muscle soreness.
  • However, lactate is a result of exertion and it’s buildup is responsible for fatigue and muscle burn. Lactate is a fuel for our performance and our organs while we exercise.
  • A healthy body is efficient in clearing lactate from its bloodstream. You can help your body by keeping hydrated and breathing properly to ensure oxygen supply to your blood.
  • Increasing our lactate threshold via aerobic training is one method to achieve a longer period of intense effort without reaching fatigue or muscle burn.
  • Even if you exercise a lot, it’s always good to boost your natural immunity, especially during the change of seasons and stressful periods of time.

Related: Holistic Lifestyle – 5 habits to get you started

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*Be mindful about your health. This article is provided for informational purposes only, and does not intend to substitute professional medical advice, diagnosis, or treatment.