links re lactic acid, lactate and carbohydrates

[Guest guest]

http://tkdtutor.com/11Training/LacticAcid.htm

http://www.cytosport.com/science/lacticacid.html

http://members.shaw.ca/bodybuilding/Muscles/Lactic_Acid.html

Did a little searching this afternoon and these links and others helped me

understand the connection between glucose and lactic acid. Note that most of

the experts on these sites are talking about normal metabolism in athletes,

but the basics were very helpful and there is some mention of excess lactic

acid or lactic acidosis and one mention of mitochondria. (pasted below)

Most of these articles were authored by university professors, either

biochemistry or exercise physiology and the information all seemed to jive.

So I think they are reasonably accurate.

Several sites were trying to dispel " myths " among athletes about lactic

acid.

There's quite a bit about pyruvate too and its role.

I also learned there is something called the Cori cycle whereby lactic

acid/lactate is recycled by the liver into glycogen via gluconeogenesis.

This was one of those aha! moments because I know that gluconeogenesis is

impaired in people with CPT deficiency. But the " backward " Cori cycle also

allows for the utilization of carbs without a large surge of insulin. Very

interesting.

Some highlights:

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 uses increasingly more carbohydrates to fuel exercise. The more you use

carbohydrates as fuel, the more lactic acid you produce.

--------------

Approximately 75% of the lactic acid made during exercise is used as fuel.

The remaining 25% is converted to glucose in the kidney and liver. The

removal of accumulated lactic acid helps avert excessively high levels, and

the conversion of lactate into glucose helps maintain sufficient levels of

blood glucose, which is important during prolonged exercise.

-------------------------

Lactic acid starts to accumulate in the muscles once you start operating

above your anaerobic threshold. This is normally somewhere between 85% and

90% of your maximum heart rate (MHR).

If your lactate threshold (LT) is reached at a low exercise intensity, it

often means that the " oxidative energy systems " in your muscles are not

working very well. If they were performing at a high level they would use

oxygen to break lactate down to carbon dioxide and water, preventing lactate

from pouring into the blood.

If your LT is low it may mean that:

---you are not getting enough oxygen inside your muscle cells

---you do not have adequate concentrations of the enzymes necessary to

oxidize pyruvate at high rates

---you do not have enough mitochondria in your muscle cells

---your muscles, heart, and other tissues are not very good at extracting

lactate from the blood.

-----------------------------

Why this backward path for liver glycogen formation? Lactate is removed much

more rapidly from the circulatory system than glucose, which expedites the

disposal of dietary carbohydrate without a tremendous insulin surge and

stimulation of fat storage.

-----------------------------------