Lactic Acid: Production, Role, and Metabolism

Lactic acid, a term often heard in the world of fitness and sports, is commonly associated with muscle fatigue. However, its role in our bodies is far more complex and beneficial than that. This article aims to shed light on the intricacies of lactic acid, its production, metabolism, and its role in sports and fitness.

What is Lactic Acid?

Lactic acid, also known as lactate, is a byproduct of anaerobic metabolism, a process that occurs when the body's oxygen levels are low. While often referred to interchangeably, lactic acid and lactate are not exactly the same.

Lactic acid is a weak acid that dissociates into lactate ion and a hydrogen ion under the pH conditions of muscle and blood. Therefore, lactate is the ion derived from the deprotonation of lactic acid. At physiological pH values, lactic acid entirely deprotonates in solution, reducing its pH.

Production and Metabolism of Lactic Acid

Lactic acid is continuously produced in the body, even at rest, and especially during physical activity. An average adult produces approximately 120 grams of lactic acid per day, with tissues having exclusively anaerobic metabolism contributing significantly to this production.

The body has mechanisms to protect itself from the potentially toxic effects of lactic acid. It can convert lactic acid back into glucose through the liver's activity or metabolize it for energy purposes in the heart. Therefore, despite its toxicity, lactic acid is not a waste product. Through various enzymatic processes, it can be used for the resynthesis of intracellular glucose.

Interestingly, recent studies suggest that lactic acid is only indirectly involved in increasing blood acidity. The primary cause of this increase is the hydrogen ion, released in high quantities during intense physical exercise due to the rise in ATP hydrolysis. This process results in a decrease in the blood's bicarbonate reserves.

The Cori Cycle

The Cori cycle is a metabolic pathway responsible for converting lactic acid into glucose. This process occurs in the liver. During strenuous muscle work, lactic acid production increases, especially in fast or pale fibers, which have higher anaerobic glycolytic power than red or resistant ones.

Lactic Acid's Role in Sports

The amount of lactic acid produced during exercise is inversely proportional to the individual's training level. This means that a sedentary person running at the same speed as an athlete will produce more lactic acid and dispose of it with greater difficulty.

During strenuous muscle work, when aerobic metabolism cannot meet the increased energy demands, an accessory pathway for ATP production, known as the anaerobic lactacid mechanism, is activated. This process increases lactic acid production, which then exceeds the body's neutralization capacity. The result is a significant increase in the amount of lactate present in the blood, which roughly corresponds to the individual's Anaerobic Threshold frequency.

Increasing Tolerance to Lactic Acid

Athletes engaged in anaerobic lactate disciplines are often in conditions of maximum lactic acid production and accumulation. Therefore, their performance is tied to the efficiency of the anaerobic lactacid metabolism and disposal systems.

Training to increase these characteristics aims to saturate the muscles with lactic acid, helping them adapt to working in conditions of strong acidity. This approach also improves the effectiveness of blood buffer systems in neutralizing blood acidosis.

Two training techniques can help improve anaerobic lactacid performance:

  1. Continuous effort: This involves 20-25 minutes of effort at heart rate values close to the anaerobic threshold.
  2. Interval work method: This involves 2-6 repetitions for 1-4 series of specific distances at race pace or higher, interspersed with partial recoveries between repetitions and complete recoveries between series.

Lactic acid is typically eliminated within 2-3 hours, and its quantity halves every 15-30 minutes, depending on the training and the amount of lactic acid produced.

Contrary to popular belief, lactic acid is not responsible for muscle pain experienced after an intense workout. This pain is caused by muscle microtears that trigger inflammatory processes. However, lactic acid does stimulate the secretion of anabolic hormones such as GH and testosterone, which can maximize muscle mass gain.

Disposing of Lactic Acid

In addition to the Cori cycle, another system helps dispose of lactic acid and prevent its accumulation in the muscle. This process is known as blood tamponade, mediated by bicarbonate.

Approximately 65% of the lactic acid produced is converted to carbon dioxide and water, 20% is converted to glycogen, 10% to protein, and 5% to glucose.

Interesting Facts About Lactic Acid

Lactic acid is not just a biological compound; it also has uses in the food industry as an acidity regulator. Furthermore, a bacterium called Lactobacillus acidophilus, found in the mouth, feeds on glucose present in food residues, forming lactic acid as a waste product. This substance can gradually dissolve tooth enamel due to its acidity.

In summary, lactic acid plays a crucial role in the body, particularly during physical activity. While often associated with muscle fatigue, it is an essential part of our metabolic processes and contributes significantly to energy production. Understanding its production, metabolism, and role can aid in optimizing physical performance and recovery.

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