How Anaerobic Metabolism and Lactic Acid Affect Your Body

Fueling muscles without oxygen produces lactic acid

Male runners jumping hurdles in race
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Anaerobic metabolism is the creation of energy through the combustion of carbohydrates in the absence of oxygen. This occurs when the lungs cannot put enough oxygen into the bloodstream to keep up with the demands from the muscles for energy. It generally is used only for short bursts of activity.

When there isn't enough oxygen in the bloodstream, glucose and glycogen cannot be fully broken down to carbon dioxide and water.

Instead, lactic acid is produced, which can build up in the muscles and degrade muscle function.

How Anaerobic Metabolism and Lactic Acid Affect You During Exercise

Lactic acid is a by-product of anaerobic glycolysis and anaerobic metabolism, both of which occur during strenuous exercise. Although lactic acid is used as a fuel by the heart, excessive lactic acid in your skeletal muscles slows down contractions, preventing you maintaining peak performance.

When the muscles use anaerobic metabolism, lactic acid is produced in the muscle cells. With moderate intensity exercise, it is able to diffuse out of the cells, but with vigorous muscle contractions it builds up.  As you build up more and more lactic acid, your muscles burn and are fatigued. Often this is felt in activities like weight lifting, but you can reach it when running or racewalking at high speed, such as sprinting. You are forced to back off and slow down so your muscles can recover and allow lactic acid to diffuse out of the cells.

It is further processed by the liver into glucose to use for fuel, completing the cycle.

Here are a few useful facts about how anaerobic metabolism affects your body during exercise:

  • When running or racewalking very fast your body turns to anaerobic metabolism to get enough energy.
  • Sprinters use anaerobic metabolism to fuel their muscles during their short burst of speed.
  • Anaerobic metabolism produces lactic acid, which can build up in the muscles to the point where you "feel the burn."
  • Fast twitch muscle fibers rely more on anaerobic metabolism for quick contractions, but they fatigue more quickly as well.
  • With high intensity intervals, you can turn a normally aerobic exercise like endurance running into an anaerobic exercise as anaerobic metabolism is needed once you exceed 90% of maximum heart rate.

How to Slow the Buildup of Lactic Acid

You can improve the point at which lactic acid builds up with specific training programs. Athletes often use these to improve their performance. They include a regimen of interval or steady state training that will bring them to their lactate threshold. It is also important to have the right diet so the muscles are well-supplied with glycogen for fuel. The lactate threshold is usually reached between 50 to 80% of an athlete's VO2 max (maximal oxygen uptake). In elite athletes it can be raised even further, allowing them to put more effort into their activities.

Anaerobic Metabolism vs. Aerobic Metabolism

Anaerobic metabolism is not as efficient as aerobic metabolism. A molecule of glucose can only produce three ATP molecules under anaerobic metabolism, while it produces 39 with aerobic metabolism.

ATP is what fuels the muscles.

Anaerobic metabolism can only use glucose and glycogen, while aerobic metabolism can also break down fats and protein. Intense bouts of exercise in the anaerobic zone and in the red-line zone with a heart rate over 80% of your maximum heart rate will result in using anaerobic metabolism to fuel the muscles.



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