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Default 08-21-2005, 09:03 AM


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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

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

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

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.
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Default 08-21-2005, 09:10 AM

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

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

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

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,

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,

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.
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Default 08-23-2005, 04:17 AM

The fourms are acting weird lately I posted on this one also.

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Default 08-23-2005, 04:53 AM

Yeah, I said earlier that there is a direct correlation between the presence of lactic acid in the body and increased levels of growth hormone.
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Default 09-25-2005, 06:56 AM

someone dont like you and deleting your posts!!

btw it sounds like i did it, I just got that power last night so it wasnt me
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