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The Build-up of Which Acid Causes Fatigue in Vigorously Exercising Muscles?

Hayley Dawes
18 October 2023

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Imagine yourself midway through an intense workout or a long-distance run. Your muscles are burning, and you’re struggling to maintain your pace. You’ve heard that the culprit behind this discomfort is lactic acid, but is that the whole story? In this comprehensive blog post, we’ll explore the relationship between lactic acid and muscle fatigue, debunk common myths, and discuss strategies to prevent and manage muscle fatigue, focusing on the build up of which acid causes fatigue in vigorously working muscles.

Short Summary

  • Lactic acid production and its effects on muscle fatigue must be examined in the context of other factors, such as H+ ions, lactate, Pi and ROS.
  • Strategies to prevent and manage muscle fatigue include proper hydration, balanced nutrition and progressive training.
  • Debunking myths about lactic acid: it is not a waste product nor does it directly cause soreness. Rather it is an important fuel source for our bodies during exercise.

Lactic Acid and Muscle Fatigue

Lactic acid is generated in muscle cells during strenuous exercise and may be associated with muscle fatigue, though it is not the only factor. Factors like H+ ions, lactate, Pi, and reactive oxygen species (ROS) also contribute to muscle weakness and fatigue. Furthermore, muscle fatigue biomarkers can be categorized into ATP metabolism biomarkers, oxidative stress biomarkers, and inflammatory biomarkers.

So, it’s crucial to understand the role of lactic acid in the context of these other factors. Let’s dive deeper into the production of lactic acid and its effects on muscle contraction and clearance.

Lactic Acid Production

Lactic acid, primarily produced in skeletal muscle and red blood cells, is a metabolic by-product resulting from the breakdown of glucose in an oxygen-deprived environment. This occurs when the body’s demand for energy exceeds the oxygen supply, leading to anaerobic metabolism.

Essentially, when our muscles are working at maximum capacity, they produce lactic acid to help meet the body’s energy needs.

Effects on Muscle Contraction

High levels of lactic acid can interfere with muscle contraction, leading to fatigue during strenuous exercise. Studies have shown that elevated levels of lactic acid diminish the quantity of calcium released from the sarcoplasmic reticulum, which is essential for muscle contraction. Furthermore, lactic acid can decrease the amount of ATP accessible for muscle contraction. This results in reduced muscle performance due to impaired calcium release and ATP availability in muscle fibers.

Central fatigue, experienced during sustained submaximal isometric contractions, has been linked to the augmentation of the central drive to the lower motoneuron pool. This enables a constant level of force to be maintained despite the development of peripheral fatigue. However, during sustained maximum voluntary contraction (MVC), the response can vary depending on the protocol and muscle under study.

Clearing Lactic Acid from Muscles

Various methods exist for clearing lactic acid from the muscles, including:

  • Active recovery exercises
  • Natural clearance over time
  • Elimination in the liver, heart, and resting and working muscles
  • Compression

Lactic acid is cleared from muscles via the circulatory system, where it is transported to the liver for conversion to pyruvate. Nutritional supplements can also aid in the recovery process and help reduce muscle fatigue.

Active recovery exercises, such as yoga or walking, can facilitate the reduction of lactic acid accumulation in the muscles by increasing blood flow and enabling the body to naturally clear it in the long run. Compression can also be beneficial in decreasing lactic acid build-up by improving circulation and aiding in the elimination of lactic acid.

Other Factors Contributing to Muscle Fatigue

While lactic acid is a significant player in muscle fatigue, other factors also contribute to this phenomenon. Dehydration, glycogen depletion, and central nervous system fatigue are all potential contributors to muscle fatigue, especially in exercising muscles.

Understanding these factors can help us better address muscle fatigue and optimize our exercise routines.


Dehydration occurs when the body loses more fluid than it takes in, leading to serious health complications if not treated promptly. Dehydration can negatively affect muscle function and lead to increased fatigue due to decreased blood flow and oxygen delivery. Ensuring adequate fluid intake is essential in order to prevent dehydration and maintain muscle performance.

Hydration can help avoid dehydration and keep electrolyte levels steady, both of which can impact muscle performance and cause fatigue. To ensure optimal hydration, it is recommended that women consume nine cups and men consume 13 cups of fluid daily.

Glycogen Depletion

Glycogen depletion refers to the reduction of the body’s stored form of carbohydrates, which is utilized to fuel muscles during exercise. Glycogen plays a significant role in providing fuel during exercise and is a major contributor to ATP regeneration during extended exercise and high-intensity intermittent exercise. There is a strong relationship between muscle glycogen content and exercise endurance.

Low-glycogen levels in skeletal muscles and/or glycolytic-derived energy can result in decreased sarcoplasmic reticulum (SR) Ca2+ release, reuptake, and Na+/K+-pump function. This highlights the importance of maintaining adequate glycogen stores to prevent muscle fatigue.

Consuming a balanced diet of carbohydrates, proteins, and fats can help maintain muscle function and facilitate recovery.

Central Nervous System Fatigue

Central nervous system fatigue refers to a state of decreased performance caused by the overstimulation of the central nervous system. This condition can negatively affect muscle performance by reducing the neural drive to muscles, making individuals experience muscle tiredness and the muscle fatigue feel. In some cases, it may be confused with chronic fatigue syndrome, which is a separate condition. Moreover, central nervous system fatigue negatively affects athletic achievement by limiting an individual’s ability to perform at their best.

Chronic pain can also lead to muscle inflammation and the weakening of muscles, as they may not be used due to the pain and discomfort it causes.

Strategies to Prevent and Manage Muscle Fatigue

Now that we have a better understanding of the factors contributing to muscle fatigue, let’s explore strategies to prevent and manage it. Implementing proper hydration, balanced nutrition, and progressive training can help us overcome muscle fatigue and improve our exercise routines.

Proper Hydration

Proper hydration involves:

  • Drinking water and other fluids when thirst is experienced
  • Consuming at least 8 glasses of fluids daily for healthy individuals
  • Men are advised to consume approximately 16 cups (3.7 liters) of fluids
  • Women are advised to consume approximately 11 cups (2.7 liters) of fluids

Maintaining adequate hydration can help reduce muscle fatigue by promoting optimal blood flow and nutrient delivery.

It is essential to ensure adequate fluid intake in order to prevent dehydration and maintain muscle performance. Consuming sufficient fluids daily can help avoid dehydration and keep electrolyte levels steady, both of which can impact muscle performance and cause fatigue.

Balanced Nutrition

A balanced diet of carbohydrates, proteins, and fats can help maintain muscle function and facilitate recovery. Consuming a variety of foods from different food groups is essential for maintaining good health, providing energy, and supplying the necessary nutrients for growth and repair. This includes:

  • Fruits
  • Vegetables
  • Dairy
  • Grains
  • Protein

Carbohydrates play an important role in providing your muscles with a sufficient supply of glycogen and other energy sources during exercise, thereby helping to prevent muscle fatigue. Therefore, incorporating proper nutrition into your daily routine is crucial in preventing and managing muscle fatigue.

Progressive Training

Progressive training is a strengthening method in which the overload is gradually increased to facilitate adaptation. This approach involves increasing:

  • the intensity
  • the weight
  • the frequency
  • the number of repetitions

In the training routine, focusing on improving physical performance over time is crucial in order to prevent plateaus and promote continuous progress in fitness and strength.

Progressive training can help enhance muscle endurance and minimize the potential of fatigue by steadily increasing exercise intensity and duration. Implementing a sensible training regime is essential when determining a course of action to improve fitness and prevent experiencing muscle fatigue, while also effectively exercising muscle.

The Role of Supplements in Combating Muscle Fatigue

In addition to proper hydration, nutrition, and progressive training, supplements can also play a role in combating muscle fatigue. Supplements such as creatine, beta-alanine, and electrolyte replenishment have been found to be beneficial in addressing muscle fatigue.

In this section, we will explore the role of these supplements in detail.


Creatine is an amino acid. It is stored in muscle tissue for use as energy. Supplementation of creatine may facilitate the production of more energy for high-intensity exercise, potentially averting or postponing muscle fatigue. It is recommended to take 3 to 6 milligrams of creatine per kilogram of body mass.

Creatine supplementation has been explored as a potential ergogenic aid. It may be helpful in improving muscle endurance. This can potentially reduce fatigue during high-intensity exercise and improve overall performance.


Beta-alanine is a non-essential amino acid that is utilized by the body to synthesize carnosine, which has been observed to enhance exercise performance. Beta-alanine has been shown to act as a buffer for muscle acidity, thereby delaying the onset of fatigue during strenuous exercise.

Beta-alanine has been shown to enhance physical activity performance, augment muscle strength and power, and delay the onset of fatigue. However, it is important to note that beta-alanine supplementation can induce the following side effects:

  • Paresthesia
  • Nausea
  • Headaches
  • Fatigue

As with any supplement, it is essential to consult a healthcare professional before incorporating beta-alanine into your routine.

Electrolyte Replenishment

Electrolyte replenishment refers to the process of restoring the levels of electrolytes in the body, which are essential for various bodily functions such as muscle contractions and maintaining fluid balance. Restoring electrolyte levels is critical for preserving adequate muscle function and avoiding exhaustion resulting from dehydration and electrolyte imbalances.

Sustaining a balanced diet and staying hydrated helps guarantee proper electrolyte replenishment. Consuming foods and beverages high in electrolytes can also aid in maintaining optimal electrolyte levels. Some examples of foods and beverages high in electrolytes include:

  • Coconut water
  • Bananas
  • Dairy products
  • Spinach
  • Kale
  • Avocados
  • Potatoes

Debunking Myths About Lactic Acid and Muscle Fatigue

There are several misconceptions surrounding lactic acid and muscle fatigue. One common myth is that lactic acid is a waste product, when in reality, it serves as an energy source for the body. Another misconception is that lactic acid is directly responsible for muscle soreness, when in fact, muscle soreness is primarily caused by microscopic muscle damage and inflammation.

Let’s delve into these myths and set the record straight.

Lactic Acid as a Waste Product

Lactic acid is not a waste product, but rather a fuel source for muscles and other tissues during exercise. During exercise, when the body is unable to produce adequate energy through aerobic respiration, anaerobic respiration occurs, resulting in lactic acid being produced as a by-product. Research has shown that lactic acid can enhance muscle contraction force and reduce fatigue during exercise.

Lactate shuttling is the process by which lactic acid is transported from the muscles to other tissues in the body, allowing it to be utilized as an energy source. This demonstrates that lactic acid is not a waste product, but rather a valuable fuel source for our bodies during exercise.

Lactic Acid and Muscle Soreness

Contrary to popular belief, lactic acid is not directly responsible for muscle soreness. Instead, muscle soreness is caused by microscopic trauma to the muscles and the connective tissue surrounding them during strenuous exercise. These micro-injuries trigger an inflammatory response, leading to the sensation of soreness and discomfort.

Lactic acid may have the following effects on the body:

  • It may reduce the rate and force of muscle contraction, resulting in fatigue and a decrease in performance.
  • However, it is not the direct cause of muscle soreness.
  • The process of lactate shuttling facilitates the clearance of lactic acid from muscles, allowing it to be utilized as an energy source in other tissues.


In this blog post, we explored the relationship between lactic acid and muscle fatigue, debunked common myths, and discussed strategies to prevent and manage muscle fatigue. We learned that while lactic acid does contribute to muscle fatigue, it is not the sole cause. Other factors, such as dehydration, glycogen depletion, and central nervous system fatigue, also play a role. By employing strategies such as proper hydration, balanced nutrition, progressive training, and supplementation, we can effectively prevent and manage muscle fatigue.

The knowledge we’ve gained about lactic acid and muscle fatigue can help us optimize our exercise routines and enhance our overall physical performance. By understanding the true causes of muscle fatigue and employing the strategies discussed in this blog post, we can push through our limits and reach new heights in our fitness journey.

Remember, the key to success in any fitness endeavor is consistency, dedication, and a well-rounded approach to exercise, nutrition, and recovery. So stay hydrated, fuel your body with the right nutrients, and keep pushing yourself to reach your goals!

Frequently Asked Questions

Which acid can build up as a result of fatigue?

Lactic acid is created when the body turns glucose into energy, causing an accumulation of hydrogen ions which increase the acidity of the blood plasma and inhibits enzyme action.

This lactic acid can build up during high-intensity exercise or anaerobic metabolism, leading to muscle fatigue and tissue damage.

Why vigorous exercise leads to muscle fatigue?

Vigorous exercise leads to muscle fatigue due to the increased level of co-contraction of antagonists muscles, an imbalance of metabolic homeostasis, production of reactive oxygen species, and lactic acid buildup.

All these factors contribute to the sensation of pain and fatigue in the muscles.

What is exercise muscle?

Exercise muscle is a type of physical activity that strengthens the body by using free weights, exercise bands, or body weight. This voluntary activity is essential for developing healthy muscle mass and strength.

Is lactic acid a waste product?

No, lactic acid is not a waste product; instead, it acts as a fuel source for muscles and other tissues during exercise.

What is the relationship between lactic acid and muscle soreness?

Lactic acid accumulation is not the primary cause of muscle soreness; it is typically caused by muscle damage and inflammation.

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