Feeling the Burn: Is it Lactic Acid?

Feeling the Burn: Is it Lactic Acid?


For a very long time we have been told that the burning sensation we feel in our muscles during intense exercise is due to accumulation of lactic acid.  We complain about lactic acid as our muscles start to tremble and fatigue before we can finish our set.  On top of that, we suffer through the delayed onset muscle soreness the next day believing that it to is a product of lactic acid.  Certain elite athletes, like Michael Phelps for instance, have been measured to have much lower blood lactate levels just after intense exercise then us mortal humans.

So lactic acid is BAD – right?  We should try to get rid of it – right?!?

Nope.  We had it all wrong.

First of all, lactate itself does not cause the burning sensation – hydrogen ions do that.  Both lactate and hydrogen ions are produced during exercise and as intensity increases, they are not recycled as quickly and they can accumulate in the muscle.  But lactate is not a waste product – it is just an intermediate.  Lactate itself is actually used as fuel in the muscle cell, and throughout the body.

Lactic acid doesn’t cause the fatigue either.  Fatigue is a result of either your muscles exceeding their oxygen supply, and/or running out of glycogen for fuel.  Lactate actually prevents fatigue by helping to prevent depolarization of the muscle cell.  Your muscle cell must stay polarized in order to contract.

What about that aching and soreness the next day?  When I can’t brush my hair because I can’t bring my arm over my head (not that I brush my hair very often), or walk down the stairs properly?  Nope.  That’s not lactic acid either.  That’s the result of microscopic tears in the muscle tissue and the inflammatory response to that damage.

Alright, well what about all these athletes and their low blood lactate levels?  Lower lactic acid must result in better performance right?

Well remember how lactate is actually a fuel that your muscles can use?  When they used to measure lactate levels, they always measured blood lactate levels.  If the lactate is in your blood, then it isn’t in your muscle cell anymore, where it could be used for fuel.  When scientists decided to measure the lactate levels inside the muscle cells themselves they discovered that normal active people are using about 75% of the lactate they produce as fuel – the other 25% is what leaks into the blood stream.  When they measured the levels of lactate inside the muscle cells of certain athletes (like Michael Phelps) they were actually producing just as much lactate during intense exercise.  But they were using over 85% of it as fuel!  So only 15% leaked into the blood – which meant lower blood lactate levels.  The scientists hypothesize that being able to use that additional 10% of the available lactate as fuel may be one of the things that gives athletes an edge.

So how do you train your body to use more lactate?  Not enough research yet to say definitively, but it looks like “lactate threshold training”, where you bring your heart rate up to 90 percent of your max and keep it there for half an hour might work.  But that sounds miserable.  Thankfully interval training also shows promise!  I’d much rather work really really hard for thirty seconds three or four times than just  pretty hard for half an hour…..

Questions? Comments? I’d love to hear from you!



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