After strenuous exercise, such as lifting heavy weights or sprinting, you may experience a burning sensation in your muscles. The culprit is lactate, or lactic acid, which in the past was viewed as a caustic waste product. However, muscles use lactate, burning it as a form of fuel in situations where oxygen is limited.
Oxygen
During less intense exercise, your body uses aerobic methods, or methods using oxygen, to power your active muscles. During more intense exercise sessions, your muscles need energy faster than the rate at which oxygen is delivered. In this latter situation, your working muscles have a method of producing energy anaerobically, or in the absence of oxygen.
Lactate
Your muscles break down glucose into pyruvate, which is converted into lactate during exercise when oxygen is scarce. Lactate allows glucose to break down, continuing energy production in the absence of oxygen. Working muscles can maintain this type of energy production at a high rate for one to three minutes. The muscles produce high levels of lactate during this time.
Effects
Lactate raises the acidity of your muscle cells and causes a deterioration in their ability to break down glucose into energy. This acts as a defense mechanism, preventing your body from sustaining a level of exertion that could cause permanent damage. After you slow down, the lactate turns back into pyruvate, permitting the aerobic methods of energy conversion to take over.
Pain
Lactate produces the burning sensation felt in active muscles, but it is not responsible for muscle soreness in the days following exercise, referred to as delayed-onset muscle soreness. Lactate leaves your muscles within an hour of exercise. Delayed muscle soreness normally peaks 24 to 72 hours after a period of intensive exercise. The cause is not known for certain, but researchers believe it may result from damage to the muscle cells and the release of certain metabolites into the tissue around the affected cells.
Interval Training
Some athletes use interval training -- short, intense bursts of exercise -- to teach their bodies how to use lactic acid as a source of fuel. Using it efficiently prevents lactate from building up in the muscles and produces more energy than the body could obtain otherwise. Interval training generates large amounts of lactate that your body learns to use quickly.
References
- "The New York Times"; Lactic Acid Is Not Muscles' Foe, It's Fuel; Gina Kolata; May 2006
- "Scientific American"; Why Does Lactic Acid Build Up in Muscles? And Why Does It Cause Soreness?; Stephen M. Roth; January 2006
- UC Berkeley News; If You "Feel the Burn," You Need to Bulk Up Your Mitochondria; Robert Sanders; April 2006
