** Lactic Acid Is Not Muscles' Foe, It's Fuel ** - nytimes 2006

[BSHC]

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

Published: May 16, 2006

 http://www.nytimes.com/2006/05/16/health/nutrition/16run.html

 

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.

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."

 http://www.nytimes.com/2006/05/16/health/nutrition/16run.html

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Muscles burn lactic acid as well as carbos

April 19, 2006

Most athletes see lactic acid as their enemy, and think that training helps them eliminate the metabolic waste product from their muscles so they will function longer and harder. But UC Berkeley physiologist George Brooks has found that training actually teaches your muscle cells how to use lactic acid as a fuel source to get more bang for the buck.

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.

1.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.

2. 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."

Source: UC Berkeley, By Robert Sanders

여기 기사내용에 긍정적이다.

젖산은 이제 싫어 할 것이 아니다. 고강도 운동에서 필연적으로 생산되고 다시 에너지로 사용되기 때문이다.

그러나 강도를 아주 미세하게 올려가면서 훈련을 쌓아 간다면 무산소 대사작용을 피하여 젖산이 생기지 않거나 극소로 생겼다가 소멸하게 하여 근력도 키우고 지구력도 키울 수 있을 것이라 생각한다.

* Lactic acid (=lactate)는  고강도 운동을 할 때 근육내에 있는 glucose를 산화 시켜 ATP를 만드는 과정에서 근육내에 만들어지는 또 하나의 다른 에너지원이다. High intensive exercise 를 할 때 는 순간에 큰 에너지가 필요하므로 근육에서 glycolysis작용이 일어나는데 산소가 충분하면 많은 에너지를 내고 물과 탄산가스가 남지만, 산소가 부족하면 적은 에너지를 내고 (ATP 생산이 유산소 때 보다 약 1/20로 적지만 순간적 폭발적 힘을 내기 위해서는 다른 방법이 없는것 같다)  lactic acid(lactate)가 남긴다. 잠간 쉬는 시간 또는 유산소 운동시에 많은 산소 호흡으로 충분한 산소를 만나면  근육내 motochondria에서 enzyme을 이용하여 Lactic acid를 산화하여 다시 ATP를 만들어 큰energy를 발생한다.

* * Lactic acid (lactate) 는 Hight intensicty exercise에서 짧은 시간에 강한 힘을 내는 과정에서 ( glycolysis) 산소부족으로 Oxygen Independent Glycolytic System에서 glucose를 완전 ATP화 하지 못하고 남은 것이다. 이것은 근육에 해로운 작용을 하지 않고 곧 다른 근육( 적근, 심장, 간)으로 혈액을 타고 흘러들어가 Oxygen Dependent Glycolytic System 으로 들어가 에너지원으로 이용된다.
( 젖산이  이것이 열감을 내거나 통증을 유발하는 것은 아니다. 열감은 에너지 발산으로 나고, 통증은 근육의 손상으로 신경을 자극하여 오는 것이다. burning을 통해 근육을 강화한다는 말은 무의미하다. 또한 다. lactic acid threshhold를 넘지 않도록 운동해야 한다 말도 의미가 없는 말이 된다.)

* 무산소운동을 한 후에는 정리운동을 통하여 혈액 순환을 돕고 충분한 산소를 마셔서 젖산을 산화하여 해소 할 필요가 있다.

* interval exercise( 고강도 저강도운동 혼합)를 하면 고강도로 생긴 젖산을 저강도에서 에너지로 소모하므로 근력과 근 지구력을 동시에 키울 수 있어 좋을 것이다.

* 피로감은 에너지 고갈에서 느낄 것이다. 저혈당이 되고 근육내 glycogen 소모가 많으면 힘이 빠진다.

* 숨을 막고 운동(무산소 운동)하면 호흡이 가쁘고 산소부족으로 머리가 띵하고 아픈 증상이 나타난다. 뇌에 산소부족으로 생명이 위험할 수도 있으니 숨을 막고 강한 힘을 쓰는 일이 있어서는 안된다. 또한 큰 힘을 써서 혈관압박을 받고 혈압상승으로 뇌 혈관 파괴가 일어날 수 있다. 무리하게 힘을 쓰는 일이 있어서도 안된다.

 hanngill

go to see 

http://cafe.daum.net/bshealthclub/LwKy/46

* 바르부르크(Otto Heinrich Warburg) 박사 (- 독일 생화학자, 세계적 암 연구학자, in 1931 awarded the Nobel Prize)는
“암세포의 발생은 산소부족에 있다고 확실히 단정하고 있다. 인체의 세포는 공기 중에 산소가 있어야 하는 유산소(aerobic) 생활을 하고 있기 때문에, 산소가 부족하면 생명을 이어 가려고 하는 생체 내의 세포는 변화를 일으키고 해당작용(glycolysis)을 비롯하여 무산소(anaerobic)생활로 바뀐다. 이렇게 바뀐 세포의 핵은 암세포의 핵과 일치한다고 생각한다.”