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Lactic Acid and Muscle Burn
Almost everything you've heard about lactic acid may be wrong.

Intense bursts of exercise can build bigger muscles.
Post-workout muscle burn isn't lactic acid...

For decades, articles have been written describing how lactic acid "builds up" during exercise and is then responsible for the burning feeling our muscles get. Lactic acid is blamed for muscle fatigue, it supposedly contributes nothing to exercise performance and it's the reason our muscles are sore after a workout.

The funny thing is, none of those statements are true. It's not your fault if you believe them, fitness professionals and columnists have been making those claims for as long as most people can remember. But endlessly repeating something that's false, doesn't make it true.

Here's what really happens to our bodies during exercise. 

Your muscles store carbohydrates from food in the form of glycogen. As you need energy, the glycogen is broken down into smaller energy units of glucose. Cells break things down even further, into pyruvate. Light and moderate exercise use the oxygen you breathe to create pyruvate and provide energy.

During intense physical bursts, you can't get enough energy from oxygen and pyruvate alone. So your body converts pyruvate into something called lactate (NOT lactic acid). Lactate can provide quick bursts of energy that last from one to three minutes. After that time, our bodies need to protect itself kicks in.

As our bodies break down and use fuels (energy), hydrogen is released. The hydrogen builds up and makes our muscles more acidic. It's much harder to breakdown glucose into energy in an acidic environment. So the energy going to your muscles starts to drop off, slowing you down. It's the hydrogen buildup and inflammation of the muscle from working it that causes muscle fatigue, not the lactate.

We evolved this mechanism for two reasons. The first is a way to give us a shot of energy during emergencies like when a wild animal suddenly appears. Then it trails off quickly, so we don't keep pushing our bodies for extended periods and damaging muscles from overexertion.

Over time, lactate helps improve endurance. Oxygen is used to break down glucose and fat for energy in little organic power plants called mitochondria. When you exercise intensely, the increased lactate production helps create more mitochondria. The more mitochondria you have, the more lactate you can use and convert to energy, increasing your endurance. It's something of a virtuous cycle.

When the workout is finished, it's not the lactate that causes soreness like we've been taught. It's simply the result of the pain we feel from damaged muscle fibers and inflammation.

Remember that our bodies are always trying to stay balanced (retain equilibrium). We're never just making pyruvate or lactate alone, they're both being produced, just at different levels based on our current physical needs.

When elite level athletes are tested, they tend to have less lactate in their blood than the average person. Because we now know how our bodies use it for energy, researchers no longer think athletes are producing less, but rather more.

An average person might have enough mitochondria to burn 70 to 75 percent of the lactate for energy, leaving 25 percent or more to escape in the bloodstream. An elite athlete may burn 80 or 90 percent of the lactate for energy, leaving as little as 10 percent to escape into the bloodstream. So when a blood test is given to the elite athlete, they show low levels of lactate. But it's not because they don't make a lot, it's because their bodies use more of it (and more efficiently) than the average person.


Lactic acid doesn't build up in muscles, it doesn't cause the burning feeling we get when we're pushing ourselves and it doesn't cause muscle fatigue or muscle soreness after a workout.

Knowing this helps explain why interval or high-intensity training is so effective. Short exercise bursts help raise lactate levels, which over time improves our ability to use energy. As we get in better condition, our bodies use lactate more efficiently and that results in the greatest performance gains.

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