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Fighting athletes' muscle fatigue
Mary Duenwald
International Herald Tribune
Thursday, August 26, 2004
NEW YORK Sprinters, weight-lifters and other athletes who push
themselves to the limit of exertion are familiar with muscle
fatigue, and many of them blame that sore, sluggish feeling on
lactic acid. But a close look at the electrical and chemical
activity that occurs within muscle fibers suggests that lactic acid,
far from causing fatigue, actually helps hard-working muscles keep
going.
Experimenting with a single muscle fiber from a laboratory rat,
researchers at La Trobe University in Melbourne and at the
University of Aarhus in Denmark observed the effects of acidity on
muscle action.
After a muscle fiber has worked intensely for a while, it begins to
lose potassium, and that dampens the fiber's ability to contract.
Lactic acid, by blocking the movement of chloride across the fiber's
surface membrane, helps the muscle fiber recover its ability to
work, said Thomas Pedersen, a doctoral student at the University of
Aarhus, co-author of the study.
The fatigue an athlete feels is probably caused by the loss of
potassium rather than the buildup of lactic acid, Pedersen said.
The finding may explain why some 100-meter runners find it
beneficial to sprint a short distance 10 to 15 minutes before a
race. "You build up a little bit of lactic acid to prepare your
muscles for the coming exertion," Pedersen said.
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Lactic Acid Is Not Muscles' Foe, It's Fuel
By GINA KOLATA
New York Times
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.
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."
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[Definitie:] "An ergogenic aid is any substance or phenomenon that enhances performance."
(Wilmore and Costill) 
