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Muscle fatigue, burning, and soreness. All of these can occur with exercise, especially if your client is new to working out. As a trainer, it’s important to understand what may be causing these issues. This helps you come up with a plan that can stop them.
One of the potential causes is lactic acid buildup. Learn what lactic acid is and how it differs from other types of muscle soreness and fatigue. We also share a few things you can do to prevent lactic acid buildup, along with how to respond if you believe this is occurring.
When exercising, the body generally uses oxygen to convert glucose to energy. During glucose breakdown, if oxygen isn’t available in adequate amounts (such as during intense exercise), lactate is produced.
Lactate can be used as energy when there is limited oxygen during exercise. This energy then fuels the working muscle. Lactate production occurs in the muscle cell. It can also be created in red blood cells.
Oftentimes, lactic acid and lactate are used interchangeably. While similar, they’re not the same thing. Lactic acid has an extra hydrogen ion, which is what makes it an acid. Once that hydrogen ion is donated, it becomes lactate.
Research indicates that lactate does not lead to muscle fatigue but, instead, is important for giving us energy even when oxygen is not available. (1) It is the lactic acid that creates the fatigue and soreness experienced with lactic acid buildup
If you’ve been using these terms to mean the same thing, you are not alone. In a letter to the editor published in the journal Physiology, the authors indicate that other researchers have done the same. (2) This leads to more confusion on this topic.
Not all muscle soreness is a result of high lactic acid levels. You can also have sore muscles for other reasons. Maybe the muscles have simply been pushed harder than they’re used to. This can occur when starting new exercise. It may also happen when intensity is ramped up. How do you know which is which?
With lactic acid muscle soreness, the soreness appears instantly. You’re in the middle of your workout, for instance, and the discomfort hits. If the soreness occurs later, this is delayed onset muscle soreness (DOMS). DOMS often presents 24 to 48 hours after exercise. This soreness is because the muscle fiber is damaged from strenuous exercise.
What would cause oxygen to not be readily available, leading to lactic acid buildup? High intensity exercise is one option to consider. In fact, one of the main causes of a high lactic acid level is intense exercise. This is referred to as exercise induced lactic acidosis. And it can occur during a cardio workout or strength training.
During an intense workout, oxygen intake can be reduced. As oxygen levels decrease, the body doesn’t have enough of this gas to turn glucose into energy. This leads to the production of lactate. With intense exercise, lactic acid can build up in the bloodstream faster than the body can get rid of it. If you exceed your lactate threshold, it can lead to a buildup.
Other factors can contribute to a high level of lactic acid in the human body. They include:
certain medical conditions, some of which include cancer, seizures, and liver failure
alcoholism and cirrhosis
infection that inflames the entire body, leading to sepsis
being in a state of shock
some medications, such as those used to treat diabetes, HIV, or AIDS
If increased lactic acid production is not a result of intense exercise, a healthcare provider should be consulted. This medical professional can help determine what is causing the lactic acid to build.
Lactic acid buildup, also known as lactic acidosis, can create a variety of effects. But how do you know if you’ve exceeded your lactate threshold, causing the lactic acid to start to accumulate? Signs of lactic acid buildup or lactic acidosis include:
a burning sensation in the muscle
muscle soreness, cramping, or muscle pain
nausea or abdominal pain
muscle fatigue or weakness
an overall feeling of fatigue and tiredness
Because these can all be signs of something else, you can’t automatically assume lactic acid buildup. It’s also possible that the client is dehydrated. This can lead to similar symptoms. They might also be coming down with the flu. This has the same type of symptoms as well.
If the symptoms come about during every exercise session, lactic acid buildup may be to blame. If they are less regular (or only occur once), something else may be causing these symptoms.
Your client is in the middle of exercise and starts to feel a burning sensation in their muscles. Or they begin to feel nauseous and their stomach starts to hurt. If you believe that they are experiencing acidosis, reduce the intensity of their exercise immediately. Transition them into a cool down. Have them take a few deep breaths and drink some water.
Then give their body time to relax before engaging in another workout session. They may even take a rest day if needed. Another option is to have them engage in active recovery. This can help reduce high lactic acid levels too.
Once they feel ready, they can try exercise again. If the muscle burn or other symptoms continue to happen, despite reducing exercise intensity, suggest that they talk to a health professional. Some other factors may be at play, causing lactate increases to the point where acidosis occurs.
If lactic acid is building as a result of a medical issue or medication, the client’s healthcare provider can help come up with a plan to ease or stop this effect. But if the lactic acid buildup is occurring due to high exercise intensity, a few modifications can help prevent this from happening.
The first is to have them start or increase exercise slowly. This gives their body (and muscle) time to adjust to the increased physical activity. With consistent exercise, their lactic acid threshold will bump higher. This reduces the likelihood that the lactate will build to high enough levels to cause the burning sensation, fatigue, and other acidosis symptoms.
Additionally, give their body enough time to recover between workout sessions. If their exercise is highly intense one day, aim for lower intensity the next day. Vary their aerobic methods so they’re not pushing their body to its limits during every workout.
It’s also important for them to stay hydrated. Drinking water helps flush the lactic acid from their system. Other benefits of adequate hydration include improved performance, reduced fatigue, and a lower risk of dehydration, the latter of which can be dangerous. Good hydration strategies include drinking before, during, and after exercise.
Diet may prevent lactic acid buildup as well. For example, a 2022 study involved 20 athletes. They all followed the same diet and training. (3) Some also received water supplemented with monk fruit. This group had lower levels of lactic acid in their blood. Other research connects probiotics with a reduction in exercise-induced lactate. (4)
Trainers can become certified nutritionists, enabling them to provide clients with personalized diet advice. If this interests you, ISSA offers Nutritionist Certification. This course is offered entirely online, providing maximum convenience.
By becoming an ISSA Nutritionist, you'll learn the foundations of how food fuels the body, plus step by step methods for implementing a healthy eating plan into clients' lifestyles.
Hall, M. M., Rajasekaran, S., Thomsen, T. W., & Peterson, A. R. (2016). Lactate: Friend or foe. PM&R, 8(3S). https://doi.org/10.1016/j.pmrj.2015.10.018
Robergs, R. A., McNulty, C. R., Minett, G. M., Holland, J., & Trajano, G. (2017). Lactate, not lactic acid, is produced by cellular cytosolic energy catabolism. Physiology, 33(1), 10–12. https://doi.org/10.1152/physiol.00033.2017
Zhou, H. (2022). Study on the role of nutrients in food to improve the motion state of athletes. Italian Journal of Food Science, 34(2), 28–33. https://doi.org/10.15586/ijfs.v34i2.2126
Jäger, R., Mohr, A. E., Carpenter, K. C., Kerksick, C. M., Purpura, M., Moussa, A., Townsend, J. R., Lamprecht, M., West, N. P., Black, K., Gleeson, M., Pyne, D. B., Wells, S. D., Arent, S. M., Smith-Ryan, A. E., Kreider, R. B., Campbell, B. I., Bannock, L., Scheiman, J., … Antonio, J. (2019). International Society of Sports Nutrition Position Stand: Probiotics. Journal of the International Society of Sports Nutrition, 16(1). https://doi.org/10.1186/s12970-019-0329-0
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