Lactate Threshold Explained… Sorta

4 08 2009

The below was written by F4 Coach  and Exercise Physiologist Adam St. Pierre.

In 1922 scientists determined that lactate was produced when carbohydrate broke down in an anaerobic environment. They also saw that increasing energy expenditure resulted in acidosis, decreasing pH of the cell.Their research never proved that lactate production resulted in acidosis, but a cause and effect relationship was assumed and not questioned for nearly 80 years!

During exercise, ATP is broken down into ADP and a phosphate molecule, releasing a hydrogen ion in the process. Under aerobic (moderate and low intensiy exercise) exercise, these hydrogen ions are used for cellular energy production. During high intensity exercise you produce more hydrogen ions than you can use for energy production and they build up in the cell. This build-up decreases the pH of the cell (increase the acidity). This acidity has been referred to by athletes and coaches as “the BURN.” I will now try to explain why lactate is not the cause of the BURN.

During intense exercise, the body breaks down carbohydrate and stored muscle glycogen to form energy quickly through glycolysis. The end product of glycolysis is pyruvate and ATP. As pyruvate builds up in the cell, energy production slows so the body converts some of that pyruvate to Lactate (pyruvate+2hydrogen ions=lactate). Lactate production is a result of cellular acidosis, not a cause. Lactate is actually a buffer molecule that serves to delay the onset of acidosis and fatigue.

So why do we even bother measuring blood lactate or talking about a lactate threshold? Despite lactate not causing fatigue, it is a good marker for fatigue (and relatively easy to measure). As you exercise harder (i.e. run faster) you produce more energy through glycolysis, therefore you produce more pyruvate, therefore you produce more lactate. Lactate leaves the muscle (pyruvate can not) and enters the blood stream where it can be taken up by other cells and used for energy (lactate can be converted back to pyruvate and used for energy aerobically (in the same way fats are used for energy). Eventually you reach your maximum sustainable energy generating capacity, called the lactate threshold. Above this speed/effort lactate begins to accumulate in the blood, it is still being produced but not being removed as quickly.

Dr. George Brooks from UC-Berkekely’s Physiology Department has done some research showing that IV infusion of lactate during exercise actually improves performance.

This kind of research excites me. At this point in time we do not know what causes fatigue. Scientists love having a question to answer!

We do know that Lactate has gotten a bad rap for a long time. Lactate is not the cause of fatigue, rather lactate is an easily measured compound that is created by your body during high intensity exercise in an effort to prolong fatigue. Lactate is a valuable molecule, essential for life and exercise.

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