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Lactic acid

Intro

Lactic acid has been blamed for soreness, injury to muscles, cramps, oxygen debt, etc. However, lactic acid is not so bad. A 2004 study found that lactic acid not only does not cause soreness, but it may also counteract fatigue. The study found that the loss of potassium is more likely the cause of fatigue.

Lactic acid has nothing to do with delayed-onset muscle soreness, the kind you feel 24–72 hours after a hard workout session. That soreness is due to the mechanical tearing of myofibrils during eccentric or lengthening contractions. In fact, if during your workout you had someone let the weight down for you on every negative or eccentric contraction so that you do just the positive or concentric reps, you would never get sore. Although concentric contractions do not produce the damage that eccentric contractions do, concentric contractions produce more lactic acid.

What is lactic acid

Lactic acid is the breakdown product of glucose and glycogen produced during a process called glycolysis. The prefix “glyco” refers to the sugar glucose (which when strung together and stored in muscle makes glycogen); “lysis” means splitting or breakdown. Lactic acid is a glucose molecule cut in half.

Glycolysis can proceed so quickly (as when you weight train) that the formation of pyruvate far exceeds the capacity of the mitochondria to accept pyruvate into the Krebs cycle (which ultimately results in the aerobic formation of ATP, the primary form of cell energy). This excess pyruvate is converted to lactic acid. The terms lactic acid and lactate are often used interchangeably, even though they are not the same compound. The lactic acid formed through glycolysis quickly releases a hydrogen ion and forms lactate.

Actively contracting muscles obtain adenosine triphosphate (ATP) from glucose stored in the bloodstream and the breakdown of glycogen stored in the muscles. Initially, pyruvic acid and small amounts of ATP are generated from the breakdown of glucose. The pyruvic acid mixed with oxygen is converted to carbon dioxide, water, and ATP.

When muscles contract vigorously for long periods, the circulatory system begins to lose ground in the delivery of oxygen. In these conditions, most of the pyruvic acid produced in the breakdown of glucose is converted to lactic acid (LA). As the lactate is produced in the muscles, it leaks into the blood and is carried around the body. If this condition continues, the functioning of the body will become impaired and the muscles will fatigue very quickly. When oxygen becomes available, the lactic acid is converted to pyruvic acid and then into carbon dioxide, water, and ATP.

Since a high level of lactate is detrimental to performance, endurance training is used to train the body to perform with a minimal amount of lactate. This may be accomplished by long steady runs, which develop the aerobic capacity through capillarization (formation of more small blood vessels, thus enhancing oxygen transport to the muscles) and by creating greater efficiency in the heart and lungs. With increased aerobic capacity, more oxygen is available to the working muscles and should delay the onset of lactic acid at a given work intensity.

Lactic threshold

Lactic acid starts to accumulate in the muscles once you start operating above your anaerobic threshold. This is normally somewhere between 85% and 90% of your maximum heart rate (MHR).
If your lactate threshold (LT) is reached at low exercise intensity, it often means that the "oxidative energy systems" in your muscles are not working very well. If they were performing at a high level, they would use oxygen to break lactate down to carbon dioxide and water, preventing lactate from pouring into the blood.

If your LT is low, it may mean that:
  • You are not getting enough oxygen inside your muscle cells.
  • You do not have adequate concentrations of the enzymes necessary to oxidize pyruvate at high rates.
  • You do not have enough mitochondria in your muscle cells.
  • Your muscles, heart, and other tissues are not good at extracting lactate from the blood.

Improving your lactic threshold

The aim is to saturate the muscles in lactic acid which will educate the body's buffering mechanism (alkaline) to deal with it more effectively. The following are example running sessions to help improve your LT:
  • 8-200 meter runs at 100% effort. With a 4 minute recovery.
  • 4-75 second reps at 100% effort. With a 5 minute recovery.
  • 5-60 second reps at 100% effort. With a 3 minute recovery.
A session should be conducted once a week and commence eight weeks before a major competition. This will help the muscle cells retain their alkaline buffering ability.

Does massage help

Many massage therapists claim one way that massage helps your muscles recover is via the enhanced removal of lactic acid. They claim you should take a warm bath in Epsom salts to rid your body further of the dreaded lactic acid. However, no evidence proves that lactic acid removal is enhanced by massages or warm baths. We do know, however, that a drop in pH due to the accumulation of lactic acid in the muscle as a result of strenuous exercise can lead to a decrease in force production (that is, your muscles get tired).

A study at the University of Northern Iowa in Cedar Falls compared the effects of massage, passive recovery, and mild bicycle riding (about 40% of max oxygen uptake) on lactate metabolism after an exhaustive treadmill run. The subjects were trained runners who performed a maximal treadmill run to elevate the level of blood lactate and induce exhaustion after 4–6 minutes.

Researchers sampled the subjects’ blood lactate for up to 20 minutes after exercise and found that passive recovery (lying down supine) and massage did not affect blood lactate levels, while mild bicycle riding caused a better removal of blood lactate 15–20 minutes after exhaustive exercise. This does not suggest that massage is useless for athletes; all it means is that the benefits of massage have nothing to do with the removal of lactic acid.

Benefits of lactic acid

First, the accumulation of lactic acid during exercise can interfere with muscle contraction, nerve conduction, and energy production, which can lead to acute fatigue. That is one reason why you tire during a training session. Yet lactic acid is not just a useless byproduct of energy metabolism—it is an important energy source.

The glucose paradox hypothesis suggests that when you ingest dietary carbohydrate, instead of it entering the liver and being converted to glycogen, it may bypass the liver, enter the circulatory system and be converted to lactic acid (in tissues such as skeletal muscle). Consequently, the lactate produced returns to the circulatory system and is converted into glycogen in the liver. Alternatively, lactate can enter the general circulation where other tissues such as the heart, liver, and kidneys can use it as fuel.

Why this backward path for liver glycogen formation? Lactate is removed much more rapidly from the circulatory system than glucose, which expedites the disposal of dietary carbohydrates without a tremendous insulin surge and stimulation of fat storage.

Lactic acid can also be used as an important fuel or as a source for glucose and glycogen synthesis. When you exercise intensely, for instance, lactic acid produced in your fast-twitch fibers can go to an adjacent slow-twitch fiber, which can then use it as fuel.

Approximately 75% of the lactic acid made during exercise is used as fuel. The remaining 25% is converted to glucose in the kidney and liver. The removal of accumulated lactic acid helps avert excessively high levels, and the conversion of lactate into glucose helps maintain sufficient levels of blood glucose, which is important during prolonged exercise.

However, that is not all lactic acid can do. Did you know that when you work your legs, for example, your inactive muscles (such as your biceps) can release lactic acid from their glycogen stores? This lactic acid travels to the liver via the bloodstream, where it is converted to glucose. This glucose is shuttled back via the blood to the previously active muscles and serves as a substrate for glycogen re-synthesis, so even your inactive muscles play a role in muscle recovery.

Since lactic acid is half the size of glucose, it more easily crosses cell membranes. Unlike glucose, which requires insulin for its transport across the cell membrane, lactic acid needs no hormonal support and crosses the membrane via facilitated transport. Also, muscles can release large quantities of lactic acid into the general circulation, where it can serve as a potential fuel source and precursor for gluconeogenesis.

Glycogen stores

A hard workout will deplete your muscles' glycogen stores. Glycogen is the fuel that powers your muscles. When you eat carbohydrates, it is stored in your liver and muscles as glycogen; however, the amount stored in your muscles is less than 400 grams.
According to studies, the most efficient time to rebuild your muscles' glycogen supply is immediately after your workout and continuing until about two hours after your workout. After two hours, your body replenishes its glycogen much more slowly. So, immediately after a workout, eat a high carbohydrate meal.

Dean Karnazes, ultramarathoner

Dean Karnazes is a man who apparently can run forever. As he runs, his lactic acid level drop so he never gets tired. Check out this link for more information on Karnazes.

Sources

  • https://www.webmd.com/fitness-exercise/guide/exercise-and-lactic-acidosis#1
  • https://www.livescience.com/lactic-acid.html#:~:text=Lactic%20acid%2C%20or%20lactate%2C%20is,muscle%20and%20red%20blood%20cells
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