10 Truths About Lactic Acid   by Aaron Ivey

Many misunderstandings exist about lactic acid, even among fitness professionals and exercise physiologists.  Here is a list of 10 things you should know about lactic acid.  The terms lactic acid and lactate will be used interchangeably in this article.  However, the truth is that lactic acid, as the acid form, is not likely to exist in the blood.  Please refer to “The Real Truth About Lactic Acid.”

1. Breaking down glucose in muscles results in the production of lactic acid.

Muscle cells break down glucose to for ATP (adenosine triphosphate), which provides the high energy bonds that are used for most chemical reactions in the body.  The byproduct lactate does not require the use of oxygen (anaerobic metabolism).  ATP production from lactate happens quickly but produces very little ATP.  It is ideal for high intensity activity that exceeds 50% of maximum capacity such as interval training.

2. Lactic acid is not responsible for muscle soreness or cramps.

Delayed onset muscle soreness, also known as DOMS is soreness that most people feel a day or two after a tough workout or a change in your workout routine.  Though some have attributed this soreness to lactic acid, research suggests that the soreness is more likely caused by damage done by the workout as well as post-exercise inflammation.  Muscle cramps may be caused by dehydration or overexcitable nerve receptors in the muscle due to fatigue.

It is common to use massage, hot baths, and other relaxation techniques to rid the muscles of “built up” lactic acid.  These remedies for muscle soreness may be beneficial for getting rid of the soreness but they have noting to do with getting rid of lactic acid build up.  Your body clears the lactate out of the blood and converts it to pyruvate, another chemical that can be used to produce ATP.

3. Lactic acid is a byproduct of carbohydrate break down for energy.

During exercise that does not rely primarily on oxygen, anaerobic exercise, such as interval training, glycogen (muscle glucose) is broken down quickly to produce ATP.  The greater the rate of glycogen breakdown the greater the production of lactate.  As the intensity of exercise increases, a greater proportion of the energy is derived from muscle glycogen which in turn produces a greater amount of lactate.

4. Lactate production occurs all the time.  It can occur even when the majority of the energy produced comes from fat sources.

Lactate production occurs during low intensity activities also.  However, the body is able process the lactate fast enough so that the levels of lactate in the blood rises only minimally.  As the intensity of exercise increases, you rely more and more on fast-twitch muscle fibers which are very efficient at burning carbohydrates.  As lactate production increases, it exceeds the rate at which the body can process lactate and convert it to pyruvate to continue the energy production process.  This increase in blood lactate levels simply means that those fast twitch muscles you have been using for your interval training are producing more lactate than the body can process.  Oxygen has little to do with it.

5. Lactic acid is continuously produced and used by many of the body’s tissues.

A delicate blood lactate balance is maintained between lactic acid production and utilization.  An increase in lactic acid concentration may simply mean a decrease in the rate of removal from blood or tissues not necessarily that the lactic acid production rate was increased.

Lactate production is proportional to the amount of carbohydrate that is used for energy production.  A portion of the carbohydrate is converted to lactate as a byproduct and then utilized by the same tissue or others in the body to produce more ATP.  Rapid break down of carbohydrates, as with interval training, accelerates production of lactate.  This lactate may temporarily build up in the muscle because it is not able to utilize it as quickly as it is produced.  Some of it may even end up in the blood stream.  However, once you lower your intensity, like during your rest phase of interval training, your body is able to clear out and use the lactate that built up.  It doesn’t take days for this clearing out to occur.

6. Lactic acid is used by the body to continue anaerobic metabolism.

Carbohydrates are digested, broken down to glucose, and enter the blood stream.  Sometimes glucose travels to the liver and is converted to muscle glucose known as glycogen.  Sometimes glucose goes directly to the muscles and is converted to lactate.  The lactate then travels to the liver where it is converted to liver glycogen.  Much of the glycogen in the liver is produced from lactate.  This is known as the “Glucose Paradox.”

7.  During long steady state exercise such as endurance races, blood lactate levels stabilize though production continues to increase throughout the event.

As blood flow increases to the muscles that are being used the most and producing the most amount of lactate, you are able to shuttle the increased lactate to other tissues.  This in turn reduces the lactate levels in your muscles even though you continue to break down carbohydrates into lactate.  As you become more conditioned your body increases its ability to clear out lactate, increased lactate threshold.

Radioactive tracers are used to discovery patterns of fuel usage in the blood and muscles.  These studies suggest that lactate production and removal continue at 300-500% of resting rates.

8. Slow twitch muscles, the heart, and respiratory muscles prefer lactate as primary fuel source.

The uptake of lactate increases in the heart as the intensity of exercise increases while the usage of glucose remains unchanged.

9. Lactic acid is a very fast fuel that is actually an athlete’s friend during intertense exercise.

After eating a meal high in carbohydrates. the  concentration of glucose and lactate increase in the blood.  Lactate is cleared out and processed pretty quickly so its concentration does not rise to high levels.  However, glucose is processed and removed from the blood much more slowly.   The body’s ability to use lactate as a fuel source actually helps to keep insulin levels lower.  Less insulin in the blood stream means that your body won’t freak out and go in to fat storage mode.

So why is lactic acid so important for regulating metabolism?  We aren’t totally sure.  However, there are a few physiological reasons that seem to make sense.  Because lactic acid is a smaller substance than glucose and some other fuel sources, it is able to be transported more readily into the cells through a process called facilitated transport.  Other fuels such as glucose depend more on slower processes to get them into the cells such as with insulin.  Lactate can also be produced rather quickly from high intensity muscle activity as was mentioned previously.  It is easier for the muscles to release lactate into the blood than to convert glycogen (muscle glucose) into glucose for mass distribution in the blood.

Some fluid replacement drinks are including lactate as part of their formulation.  The rationale for that is that since glucose is converted to lactate anyways and lactate can provide a faster energy source during intense exercise, why not use it in a drink?  Lactate in the drink can also provide a great source of building blocks to restore glycogen levels in the muscle.

10. Specific training can help the body become more efficient removing lactate from your muslces.

High intensity interval training is perfect for training your body to use lactate more efficiently.  This is critical for an athlete to compete at their best.  It is also important for coaches to know how to train their athletes to most effectively prepare them for their sport or event.  Fortunately, most training programs incorporate elements necessary to speed lactate removal. Training programs should build your capacity to remove lactic acid during competition.

Training programs should aim to tax your body’s ability to process lactic acid production.  Increased intensity and training at a level that exceeds the body’s ability to remove lactate (lactate threshold) will help it to become more efficient.  Training at or above your lactate threshold stimulates your body to produce enzymes that speed the use of lactic acid as a fuel.

High intensity interval training will cause cardiovascular adaptations that increase oxygen delivery to your muscles and tissues. Consequently, you have less need to breakdown carbohydrate to lactic acid. Also, better circulation helps speed the transport of lactic acid to tissues that can remove it from the blood.

“Feel the burn!” The lactic acid myth revealed!

You hear it all the time in the gym when you feel that burn in the muscle. “Oh that is the lactic acid building up in your muscle. That is why it burns.” Is that really what is happening or is there some other chemical or physiological explanation for the burn you feel. You have probably been sore a day or two after a good workout. Again, some attribute this to lactic acid build up. Can there be another explanation for this?

Yes! The idea that lactic acid is the cause of such discomfort is not supported by basic biochemistry, the chemical reactions that take place in your body. It is true that lactic acid exists. However, lactic acid is not the cause of the soreness or the burn.

Maybe a quick summary of basic chemistry will help. Acids are made up of a “free” hydrogen molecule (not chemically combined with another substance) and a salt molecule such as lactate. Under the right conditions, these two molecules chemically combine to form an acid. One of the most common acids is hydrochloric acid. The number of hydrogen molecules that are “free” determines the pH of a solution. The measure of the concentration of free hydrogens in a solution is known as pH. A lower pH value means that the solution or environment has a greater concentration of free hydrogens (more acidic). A higher pH value means that the solution has a lower concentration of free hydrogens. We call this basic or alkaline.

The value of pH is measured on a scale from 0 to 14. Stomach acid has a pH of around 2. Water has a pH of around 7 and liquid drain cleaner has a pH of around 14. When you combine a base and an acid, the solution moves closer to the neutral pH around 7. That is why you add baking soda to your pool if the pH is too low and muriatic acid if the pH is too low. By doing so you are providing a salt for the hydrogen to bond to thereby reducing the concentration of free hydrogens. This increases the pH

At a pH of 3.86 lactate bonds with free hydrogens to form lactic acid. However, when the pH is greater than 3.86 lactic acid becomes sodium lactate and does not contribute to the free hydrogens in the blood, which has a pH of around 7. Even during intense exercise the pH of blood does not drop very far below this. Therefore, lactic acid really does not exist in the body. In fact, the production of lactate in the blood during exercise helps to make the blood more basic and neutralize the pH.

The burn you feel during your workout is not a result of lactic acid. Nor is lactic acid the so-called “toxin” that is released when you get a massage. But that’s another story…

For more detailed information on the biochemistry involved please see the following article by Robert A Robergs:
Exercise-Induced Metabolic Acidosis: Where do the Protons come from?

Interval Training

Lactic Acid Not Athlete’s Poison, But An Energy Source — If You Know How To Use It

ScienceDaily (Apr. 21, 2006) — In the lore of marathoners and extreme athletes, lactic acid is poison, a waste product that builds up in the muscles and leads to muscle fatigue, reduced performance and pain.

Some 30 years of research at the University of California, Berkeley, however, tells a different story: Lactic acid can be your friend.

Coaches and athletes don’t realize it, says exercise physiologist George Brooks, UC Berkeley professor of integrative biology, but endurance training teaches the body to efficiently use lactic acid as a source of fuel on par with the carbohydrates stored in muscle tissue and the sugar in blood. Efficient use of lactic acid, or lactate, not only prevents lactate build-up, but ekes out more energy from the body’s fuel.

In a paper in press for the American Journal of Physiology – Endocrinology and Metabolism, published online in January, Brooks and colleagues Takeshi Hashimoto and Rajaa Hussien in UC Berkeley’s Exercise Physiology Laboratory add one of the last puzzle pieces to the lactate story and also link for the first time two metabolic cycles – oxygen-based aerobic metabolism and oxygen-free anaerobic metabolism – previously thought distinct.

“This is a fundamental change in how people think about metabolism,” Brooks said. “This shows us how lactate is the link between oxidative and glycolytic, or anaerobic, metabolism.”

He and his UC Berkeley colleagues found that muscle cells use carbohydrates anaerobically for energy, producing lactate as a byproduct, but then burn the lactate with oxygen to create far more energy. The first process, called the glycolytic pathway, dominates during normal exertion, and the lactate seeps out of the muscle cells into the blood to be used elsewhere. During intense exercise, however, the second ramps up to oxidatively remove the rapidly accumulating lactate and create more energy.

Training helps people get rid of the lactic acid before it can build to the point where it causes muscle fatigue, and at the cellular level, Brooks said, training means growing the mitochondria in muscle cells. The mitochondria – often called the powerhouse of the cell – is where lactate is burned for energy.

“The world’s best athletes stay competitive by interval training,” Brooks said, referring to repeated short, but intense, bouts of exercise. “The intense exercise generates big lactate loads, and the body adapts by building up mitochondria to clear lactic acid quickly. If you use it up, it doesn’t accumulate.”

To move, muscles need energy in the form of ATP, adenosine triphosphate. Most people think glucose, a sugar, supplies this energy, but during intense exercise, it’s too little and too slow as an energy source, forcing muscles to rely on glycogen, a carbohydrate stored inside muscle cells. For both fuels, the basic chemical reactions producing ATP and generating lactate comprise the glycolytic pathway, often called anaerobic metabolism because no oxygen is needed. This pathway was thought to be separate from the oxygen-based oxidative pathway, sometimes called aerobic metabolism, used to burn lactate and other fuels in the body’s tissues.

Experiments with dead frogs in the 1920s seemed to show that lactate build-up eventually causes muscles to stop working. But Brooks in the 1980s and ’90s showed that in living, breathing animals, the lactate moves out of muscle cells into the blood and travels to various organs, including the liver, where it is burned with oxygen to make ATP. The heart even prefers lactate as a fuel, Brooks found.

Brooks always suspected, however, that the muscle cell itself could reuse lactate, and in experiments over the past 10 years he found evidence that lactate is burned inside the mitochondria, an interconnected network of tubes, like a plumbing system, that reaches throughout the cell cytoplasm.

In 1999, for example, he showed that endurance training reduces blood levels of lactate, even while cells continue to produce the same amount of lactate. This implied that, somehow, cells adapt during training to put out less waste product. He postulated an “intracellular lactate shuttle” that transports lactate from the cytoplasm, where lactate is produced, through the mitochondrial membrane into the interior of the mitochondria, where lactate is burned. In 2000, he showed that endurance training increased the number of lactate transporter molecules in mitochondria, evidently to speed uptake of lactate from the cytoplasm into the mitochondria for burning.

The new paper and a second paper to appear soon finally provide direct evidence for the hypothesized connection between the transporter molecules – the lactate shuttle – and the enzymes that burn lactate. In fact, the cellular mitochondrial network, or reticulum, has a complex of proteins that allow the uptake and oxidation, or burning, of lactic acid.

“This experiment is the clincher, proving that lactate is the link between glycolytic metabolism, which breaks down carbohydrates, and oxidative metabolism, which uses oxygen to break down various fuels,” Brooks said.

Post-doctoral researcher Takeshi Hashimoto and staff research associate Rajaa Hussien established this by labeling and showing colocalization of three critical pieces of the lactate pathway: the lactate transporter protein; the enzyme lactate dehydrogenase, which catalyzes the first step in the conversion of lactate into energy; and mitochondrial cytochrome oxidase, the protein complex where oxygen is used. Peering at skeletal muscle cells through a confocal microscope, the two scientists saw these proteins sitting together inside the mitochondria, attached to the mitochondrial membrane, proving that the “intracellular lactate shuttle” is directly connected to the enzymes in the mitochondria that burn lactate with oxygen.

“Our findings can help athletes and trainers design training regimens and also avoid overtraining, which can kill muscle cells,” Brooks said. “Athletes may instinctively train in a way that builds up mitochondria, but if you never know the mechanism, you never know whether what you do is the right thing. These discoveries reshape fundamental thinking on the organization, function and regulation of major pathways of metabolism.”

Brooks’ research is supported by the National Institutes of Health.

University of California – Berkeley (2006, April 21). Lactic Acid Not Athlete’s Poison, But An Energy Source — If You Know How To Use It.