Lactic Acid and Muscle Fatigue

What is anaerobic muscular function?

When the muscles are working at a high intensity, the cardiovascular and respiratory systems cannot deliver oxygen fast enough for the muscles to function aerobically. In this situation, the muscles go into anaerobic function, or function without the presence of oxygen.

The Formation of Lactic Acid:

Lactic acid is a byproduct of the chemical reaction between glucose and oxygen.

C6H12O6 C3H6O3 + (smaller amount of) Energy

Glucose and oxygen react during anaerobic respiration. The energy produced in this reaction is used by the muscles for contraction. Lactic acid builds up in the muscles, causing fatigue, and eventually muscle failure.

What is the Function of Lactic Acid?

During anaerobic function, muscular cells convert glucose or glycogen to lactic acid. Lactic Acid is used as fuel in the mitochondria. The mitochondria have a unique protein that transports the lactic acid into them, where it can then be converted into usable energy for the muscles.

The Cycle of Lactic Acid:

(https://thefitnessgrail.wordpress.com/2012/04/01/lactic-acid-training-for-fat-loss/)

Lactic Acid Recovery:

Oxygen must be present to rid the muscles of lactic acid build-up. The body has responses to excess lactic acid that ensure sufficient oxygen is present to clear the lactic acid. Due to the high concentration of CO2 in the blood, part of the brain, called the medulla oblongota, alters the blood's pH. Meanwhile, the respiratory rate and heart rate increases to bring more oxygen into the body and deliver it to the muscles.

The recovery time - during which the body's heart and respiratory rates slow and come back to normal - depends on the person's fitness, but is typically between twelve and sixteen seconds. All the lactic acid is cleared from the muscles within an hour after intense exersize.

What is Lactic Acid?

Lactic acid is the byproduct of anaerobic glucose metabolism. It is produced during muscle contraction when the muscles are working anaerobically.

The chemical formula for lactic acid is C3H6O3. It is a water-soluble substance. Its consistency is syrup-like, and it is typically colorless or slightly yellow.

Lactic Acid Molecular Structure:

What is the Connection between Lactic Acid and Muscle Fatigue?

Muscle Fatigue:

The buildup of lactic acid causes muscle fatigue. The muscles can only function for a short amount of time (this length depends on the person's fitness) when lactic acid is present. After lactic acid floods the muscles, the muscles give out and cannot function until the lactic acid has been cleared.

Lactic acid does not cause delayed-onset muscle soreness (DOMD). This is caused by microscopic tears in the muscle fibers.

Sources:

Burke, Edmund R., Ph.D. "It's Not About the Lactic Acid: Why You're Still Sore After Yesterday's Ride." ACTIVE.com. N.p., n.d. Web. 23 Mar. 2017.

Kolata, Gina. "Lactic Acid Is Not Muscles' Foe, It's Fuel." The New York Times. The New York Times, 15 May 2006. Web. 23 Mar. 2017.

"Lactic Acid." Dictionary.com. Dictionary.com, n.d. Web. 23 Mar. 2017.

"Lactic Acid Formation." Formation of Lactic Acid in Muscles (Simple Explanation). IvyRose Holistic, n.d. Web. 23 Mar. 2017.

The Lactic Acid Cycle. Digital image. The Fitness Grail. N.p., n.d. Web.

Lactic Acid and Muscle Fatigue

Brooke Doughty

Chemistry

Unit 3, Week 6