It seems that almost every conversation about resistance training or anaerobic activity always centers on “The Burn”. I’m talking about that deep burning sensation in your muscles that feels hot or stingy when reaching muscle exhaustion during weight training or short burst energy activities like sprinting. What exactly causes that burning sensation and is it a sign that you’re exercising correctly?
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Without getting too technical, that burning sensation is caused by a buildup of lactic acid. When we do exercise for short periods of time (up to 3 minutes), our bodies are in an anaerobic state. Anaerobic means “without oxygen” and means that when we need immediate energy, oxygen is not a readily available source of energy. So, our body relies on another form of quick release energy called glucose. When this happens, glucose is broken down into pyruvate and when we are in anaerobic activity, pyruvate is converted into lactate. When your body has high levels of lactate (lactic acid), there is also an increase in the acidity of the muscle cells themselves which creates that burning sensation. This is exactly why when you are truly in an aerobic state, you do not feel “The Burn”.
Although there are those that believe lactic acid is what causes us to have DOMS (Delayed Onset Muscle Soreness), it has never been proven that this is the case. Muscle soreness is caused by microscopic muscle fiber damage. When you have muscle fiber damage from exercise, your muscles become inflamed and swell which is what causes the soreness you feel from exercise during the next 2-3 days afterwards.
There you have it, the truth on lactic acid. It’s a perfectly natural part of exercise and is the direct result of spent energy during anaerobic activity. So, the next time you here a conversation pairing that burning sensation with muscle soreness; you can step right in and tell the burning truth.
Bobby Whisnand 