NYTimes:Lactic Acid is Muscle Fuel


Lactic Acid Is Not Muscles' Foe, It's Fuel


Published: May 16, 2006

Everyone who has even thought about exercising has heard the warnings about lactic acid. It builds up in your muscles. It is what makes your muscles burn. Its buildup is what makes your muscles tire and give out.
Skip to next paragraph
Ben Stansall/European Pressphoto Agency

Coaches and personal trainers tell athletes and exercisers that they have to learn to work out at just below their "lactic threshold," that point of diminishing returns when lactic acid starts to accumulate. Some athletes even have blood tests to find their personal lactic thresholds.

But that, it turns out, is all wrong. Lactic acid is actually a fuel, not a caustic waste product. Muscles make it deliberately, producing it from glucose, and they burn it to obtain energy. The reason trained athletes can perform so hard and so long is because their intense training causes their muscles to adapt so they more readily and efficiently absorb lactic acid.

The notion that lactic acid was bad took hold more than a century ago, said George A. Brooks, a professor in the department of integrative biology at the University of California, Berkeley. It stuck because it seemed to make so much sense.

"It's one of the classic mistakes in the history of science," Dr. Brooks said.

Its origins lie in a study by a Nobel laureate, Otto Meyerhof, who in the early years of the 20th century cut a frog in half and put its bottom half in a jar. The frog's muscles had no circulation -- no source of oxygen or energy.

Dr. Myerhoff gave the frog's leg electric shocks to make the muscles contract, but after a few twitches, the muscles stopped moving. Then, when Dr. Myerhoff examined the muscles, he discovered that they were bathed in lactic acid.

A theory was born. Lack of oxygen to muscles leads to lactic acid, leads to fatigue.

Athletes were told that they should spend most of their effort exercising aerobically, using glucose as a fuel. If they tried to spend too much time exercising harder, in the anaerobic zone, they were told, they would pay a price, that lactic acid would accumulate in the muscles, forcing them to stop.

Few scientists questioned this view, Dr. Brooks said. But, he said, he became interested in it in the 1960's, when he was running track at Queens College and his coach told him that his performance was limited by a buildup of lactic acid.

When he graduated and began working on a Ph.D. in exercise physiology, he decided to study the lactic acid hypothesis for his dissertation.

"I gave rats radioactive lactic acid, and I found that they burned it faster than anything else I could give them," Dr. Brooks said.

It looked as if lactic acid was there for a reason. It was a source of energy.

Dr. Brooks said he published the finding in the late 70's. Other researchers challenged him at meetings and in print.

"I had huge fights, I had terrible trouble getting my grants funded, I had my papers rejected," Dr. Brooks recalled. But he soldiered on, conducting more elaborate studies with rats and, years later, moving on to humans. Every time, with every study, his results were consistent with his radical idea.

Eventually, other researchers confirmed the work. And gradually, the thinking among exercise physiologists began to change.

"The evidence has continued to mount," said L. Bruce Gladden, a professor of health and human performance at Auburn University. "It became clear that it is not so simple as to say, Lactic acid is a bad thing and it causes fatigue."

As for the idea that lactic acid causes muscle soreness, Dr. Gladden said, that never made sense.

"Lactic acid will be gone from your muscles within an hour of exercise," he said. "You get sore one to three days later. The time frame is not consistent, and the mechanisms have not been found."

The understanding now is that muscle cells convert glucose or glycogen to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.

Mitochondria even have a special transporter protein to move the substance into them, Dr. Brooks found. Intense training makes a difference, he said, because it can make double the mitochondrial mass.

It is clear that the old lactic acid theory cannot explain what is happening to muscles, Dr. Brooks and others said.

Yet, Dr. Brooks said, even though coaches often believed in the myth of the lactic acid threshold, they ended up training athletes in the best way possible to increase their mitochondria. "Coaches have understood things the scientists didn't," he said.

Through trial and error, coaches learned that athletic performance improved when athletes worked on endurance, running longer and longer distances, for example.

That, it turns out, increased the mass of their muscle mitochondria, letting them burn more lactic acid and allowing the muscles to work harder and longer.

Just before a race, coaches often tell athletes to train very hard in brief spurts.

That extra stress increases the mitochondria mass even more, Dr. Brooks said, and is the reason for improved performance.

And the scientists?

They took much longer to figure it out.

"They said, 'You're anaerobic, you need more oxygen,' " Dr. Brooks said. "The scientists were stuck in 1920."

Hmmm very interesting

"I need to learn how to apply this now. This changes lots, I was just explaining the lactic acid theory to my gf last night, now I feel like a dummy!"

No reason to. Knowledge is fluid not static.

  • goes to GNC and waits for new Xyience NOX-CG3-LA *

People who do their own research have known this for decades.  Shit, anyone who's watched "The Science of Lance Armstrong" already knew this too.  Lance's body uses lactic acid for energy at a crazy efficient rate.    

passedgas is correct, thanks.


the article is correct with respect to DOMS.

however, an alternate explanation is that the body, through adaptation, becomes more efficient at increasing the lactate threshold.

i'm not ready to throw the krebs cycle out the window b/c of one article.

For those that want to read more:

10 THINGS YOU SHOULD KNOW ABOUT LACTIC ACID: OLD MYTHS AND NEW REALITIES, by Thomas Fahey, Ed.D., Professor of Exercise Physiology, California State University at Chico

Lactic acid has a bad reputation. Many people blame it for fatigue, sore muscles, and cramps. They think of it as a waste product that should be avoided at all cost. Guess what? Scientists have discovered that lactic acid plays a critical role in generating energy during exercise. Far from being the bad boy of metabolism, lactic acid provides fuels for many tissues, helps use dietary carbohydrates, and serves as fuel for liver production of glucose and glycogen. In fact, lactic acid is nature's way of helping you survive stressful situations.

Lactic acid has a dark side. When your body makes lactic acid, it splits into lactate ion (lactate) and hydrogen ion. Hydrogen ion is the acid in lactic acid. It interferes with electrical signals in your muscles and nerves, slows energy reactions, and impairs muscle contractions. The burn you feel in intense exercise is caused by hydrogen ion buildup. So, when you fatigue, don't blame it on lactic acid. Rather, place the blame where it belongs- on hydrogen ion.

Lactate has been made guilty by association. Far from being a metabolic pariah, the body loves lactate. It is an extremely fast fuel that's preferred by the heart and muscles during exercise. Lactate is vital for ensuring that your body gets a steady supply of carbohydrates, even during exercise that lasts for many hours. Lactate is so valuable, that taking it as part of a fluid replacement drink before, during, or after exercise improves performance and speeds recovery.

Lactate is a friend to triathletes, distance runners, swimmers, and cyclists. When you learn the facts about lactic acid, you will think of it in a whole new light. Harness the power of lactic acid and you will increase your energy level and stave off fatigue.


Here are ten things you should know about lactic acid:

1. Lactic acid is formed from the breakdown of glucose.
During this process the cells make ATP (adenosine triphosphate), which provides energy for most of the chemical reactions in the body. Lactic acid formation doesn't use oxygen, so the process is often called anaerobic metabolism. Lactate-related ATP production is small but very fast. This makes it ideal for satisfying energy needs anytime exercise intensity exceeds 50% of maximum capacity.

2. Lactic acid doesn't cause muscle soreness and cramps.
Delayed onset muscle soreness, the achy sensation in your muscles the day after a tough workout, is caused by muscle damage and post-exercise tissue inflammation. Most muscle cramps are caused by muscle nervous receptors that become overexcitable with muscle fatigue.

Many athletes use massage, hot baths, and relaxation techniques to help them rid their muscles of lactic acid and thus relieve muscle soreness and cramping. While these techniques probably have other benefits, getting rid of lactic acid isn't one of them. Lactate is used rapidly for fuel during exercise and recovery and doesn't remain in the muscles like motor oil.

3. The body produces lactic acid whenever it breaks down carbohydrates for energy.
The faster you break down glucose and glycogen the greater the formation of lactic acid. At rest and submaximal exercise, the body relies mainly on fats for fuel. However, when you reach 50% of maximum capacity, the threshold intensity for most recreational exercise programs, the body "crosses over" and used increasingly more carbohydrates to fuel exercise. The more you use carbohydrates as fuel, the more lactic acid you produce.

4. Lactic acid can be formed in muscles that are receiving enough oxygen.
As you increase the intensity of exercise, you rely more and more on fast-twitch muscle fibers. These fibers use mainly carbohydrates to fuel their contractions. As discussed, whenever you break down carbohydrates for energy, your muscles produce lactic acid. The faster you go, the more fast-twitch muscles you use. Consequently, you use more carbohydrates as fuel and produce more lactic acid. Increased blood lactic acid means only that the rate of entry of lactic acid into the blood exceeds the removal rate. Oxygen has little to do with it.

5. Many tissues, particularly skeletal muscles, continuously produce and use lactic acid.
Blood levels of lactic acid reflect the balance between lactic acid production and use. An increase in lactic acid concentration does not necessarily mean that the lactic acid production rate was increased. Lactic acid may increase because of a decreased rate of removal from blood or tissues.

Lactic acid production is proportional to the amount of carbohydrates broken down for energy in the tissues. Whenever you use carbohydrates, a significant portion is converted to lactate. This lactate is then used in the same tissues as fuel, or it is transported to other tissues via the blood stream and used for energy. Rapid use of carbohydrate for fuel, such as during intense exercise, accelerates lactic acid produciton. Temporarily, lactic acid builds up in your muscles and blood because it can't be used as fuel fast enough. However, if you slow down the pace of exercise or stop exercising, the rate of lactate used for energy soon catches up with the rate of lactate production.

Dr. George Brooks, a Professor from the Department of Integrative Biology at University of California at Berkeley, described the dynamic production and use of lactic acid in metabolism in his "Lactate Shuttle Theory." This theory describes the central role of lactic acid in carbohydrate metabolism and it's importance as a fuel for metabolism.

6. The body uses lactic acid as a biochemical "middleman" for metabolizing carbohydrates.
Carbohydrates in the diet are digested and enter the circulation form the intestines to the liver mainly in the form of glucose (blood sugar). However, instead of entering the liver as glucose and being converted directly to glycogen, most glucose from dietary carbohydrate bypasses the liver, enters the general circulation and reaches your muscles and converts into lactic acid. Lactic acid then goes back into the blood and travels back to the liver where it is used as building blocks for making liver glycogen. Your body produces much of its liver glycogen indirectly from lactic acid rather than directly from blood glucose.

Scientists call the process of making liver glycogen from lactic acid the "Glucose Paradox". The theory was formulated by famous biochemist Dr. J.D. McGarry and his associates. It shows the importance of lactic acid in carbohydrate metabolism.


7. During endurance races, such as marathons and triathlons, blood lactic acid levels stabilize even though lactic acid production increases.
This occurs because your capacity to produce lactic acid is matched by your ability to use it as fuel. Early during a race, there is a tremendous increase in the rates that muscle uptake and use glucose and breakdown glycogen. The increased rate of carbohydrate metabolism steps up production of muscle lactic acid, which also causes an increase in blood lactic acid.

As your body directs blood to your working muscles, you can shuttle the lactate to other tissues and use it as fuel. This reduces lactic acid levels in your muscles and blood, even though you continue to produce great quantities of lactic acid. However, you often feel better during the race or training. This relief is sometimes called "second wind".

Scientists use radioactive tracers to follow the use pattern of fuels in your blood and muscles. Their studies show that during exercise, lactic acid production and removal continue at 300-500 percent of resting rates, even though oxygen consumption has stabilized at submaximal levels.

8. The heart, slow-twitch muscle fibers, and breathing muscles prefer lactate as a fuel during exercise.
In the heart, for example, the uptake of lactate increases many fold as the intensity of exercise increases while uptake of glucose remains unchanged. These tissues suck up lactate at a fast rate to satisfy their energy needs.

9. Lactic acid is a very fast fuel that can be used to athletes' advantage during exercise.
The concentration of both glucose and lactic acid rise in the blood after a carbohydrate-rich meal, but the blood lactic acid concentration does not rise much because it is removed so rapidly. The body converts glucose, a substance removed from the blood only sluggishly, to lactate, a substance removed and used rapidly. Using lactic acid as a carbohydrate "middleman" helps you get rid of carbohydrates from your diet, without increasing insulin or stimulating fat synthesis. During exercise, you won't want an increase in insulin because it decreases the availability of carbohydrates that are vital to high performance metabolism.

Why is lactic acid so important in metabolic regulation? The exact answer is unknown, but there do appear to be several physiological reasons. Lactic acid- in contrast to glucose and other fuels- is smaller and better exchanged between tissues. It moves across cell membranes by a rapid process called facilitated transport. Other fuels need slower carrier systems such as insulin. Also, lactate is made rapidly in large quantities in muscle and released into general circulation. Muscle cells with large glycogen reserves cannot release significant amounts of this potential energy source as glucose because muscle lacks a key enzyme required to produce free glucose that can be released to the blood.

Including lactate as part of a fluid replacement beverage provides a rapid fuel that can help provide energy during intense exercise. The rationale for including lactate in athletic drinks is simple- since the body breaks down so much of dietary carbohydrates to lactate anyway, why not start with lactate in the first place? Lactate in the drink can be used rapidly by most tissues in the body and serves as readily available building blocks for restoring liver glycogen during recovery.

10. Proper training programs can speed lactic acid removal from your muscles.
This can be achieved by combining high intensity, interval, and over-distance training. Athletes and coaches must learn to deal effectively with lactic acid. Fortunately, most training programs incorporate elements necessary to speed lactate removal. Training programs should build your capacity to remove lactic acid during competition.

Lactic acid formation and removal rates increase as you run, bike or swim faster. To improve your capacity to use lactate as a fuel during exercise, you must increase the lactic acid load very high during training. Training with a lot of lactic acid in your system 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.

Over distance training causes muscular adaptations that speed the rate of lactate removal. Over distance training in running, swimming, or cycling increases muscle blood supply and the mitochondrial capacity. Mitochondria are structures within the cells that process fuels, consume oxygen, and produce large amounts of ATP. A larger muscle mitochondrial capacity increases the use of fatty acids as fuel, which decreases lactate formation and speeds its removal.


Nutrition is also important, strenuous training depletes glycogen reserves in the muscle and liver. A diet high in carbohydrates is essential for all endurance athletes. Carbohydrates supply an immediate source of glucose so the athlete has a feeling of well-being and a source of quick energy. Further, glucose is used to restore muscle glycogen from exercise. When the blood glucose and muscle glycogen reserves are renewed, glucose provides a source of lactate that helps replenish liver glycogen.


Lactic acid is an important fuel for the body during rest and exercise. It is used to synthesize liver glycogen and is one of our most important energy sources. Lactate is the preferred fuel source in highly oxidative tissues, such as heart muscle and slow-twitch skeletal muscle fibers. It is used rapidly by the body and is a valuable component in athletic fluid replacement beverages.

Lactic acid also is a powerful organic acid, and its accumulation can cause distress and fatigue during exercise. Athletes need both high intensity and over-distance training to improve the capacity to use lactic acid as a fuel during exercise and recovery. High intensity training develops cardiovascular capacity that reduces lactic acid transport to tissues that can use it as fuels. Over distance training causes tissue enzymes adaptations that increase use of fatty acids for energy. This helps slow lactic acid production from carbohydrates and to enhance tissues ability to use lactic acid as fuel.


Ahlborg G., Felig P. Lactate and glucose exchange across the forearm, legs and splanchnic bed during and after prolonged leg exercise. J. Clin. Invest. 69: 45-54. 1982.

Ahlborg G., Wahren J., Felig R. Splanchnic and peripheral glucose and lactate metabolism during and after prolonged arm exercise. J. Clin. Invest. 77: 690-699, 1986.

Brooks G.A., Fahey T.D., White T. Exercise Physiology: Human Bioenergetics and Its Applications. Mt. View, CA: Mayfield Publishing Co., 1985.

Brooks, G.A. Lactate production under fully aerobic conditions. The lactate shuttle during rest and exercise. Fed. Proc. 45: 2924-2929, 1986.

Brooks, G.A. Mammalian fuel utilization during sustained exercise. Comp. Biochem. Physiol. 120: 89-107, 1998.

Brooks, G.A., Mercier J. The balance of carbohydrate and lipid utilization during exercise: the crossover concept (brief review). J. Appl. Physiol. 80: 2253-2261, 1994.

Brooks, G.A. and Trimmer J.K. Glucose kinetics during high-intensity exercise and the crossover concept. J. Appl. Physiol. 80: 1073-1074, 1996.

Donovan C.M., Brooks G.A. Endurance training affects lactate clearance, not lactate production. Am. J. Physiol. 244: E83-E92, 1983.

Hultman E.A. Fuel selection muscle fiber. Proc. Nutr. Soc. 54: 107-121, 1995.

Zinker B.A., Wilson R.D., Wasserman D.H. Interaction of decreased arterial PO2 and exercise on carbohydrate metabolism in the dog. Am. J. Physiol. 269: E409-E417, 1995.

Bottomline: You need more oxygen. Practically nothing in your body is coverted to anything with out the breaking down of oxygen (aerobic cyles). To help neutralize the lactic acid and to help metabolize it you need O2.

Nothing new.