Fitness Myth Busting Part 1: Lactic Acid

The fitness world is full of myths, legends, and downright BS. Sometimes I think it’s harder for people to sift through the nonsense on the internet than it is for them to complete their first workout.

Should I lift weights? Should I do cardio? Should I NEVER do steady state cardio? Will I get bulky? Higher reps, lower reps, heavy, light…wait, WHAT?

There are a thousand questions you can ask about fitness and exercise, and odds are you’ll get a different answer for each of them depending on who you ask. While there are some things out there that are just a matter of differing opinions, there are others that are continuously shared in the fitness world, despite heaps of evidence and science disproving (or at least strongly questioning) their validity.

I was going to take today to talk about 3 of the top three fitness myths out there, and why you need to stop believing in them, stat. However, once I got started on the first one, I realized it was a post in itself. The other two in this series will be coming soon, but for now, myth #1!

The Lactic Acid Myth

We’ve all heard it: if you work out at a high intensity, lactic acid will build up in your muscles. And if you don’t do something to “get it out” at the end of your workout, it will stay there and cause soreness later on. I’ve always pictured this like Ghostbusters slime that seeps into your muscle belly and just sits there for all of eternity.

So, what’s the truth here? Well, get ready for the shock of your life:

Lactic acid doesn’t “build up” in muscles. In fact, lactic acid basically doesn’t exist.

*Mic drop*

So, that thing you’ve been hearing about since your days as a middle school track star is nonexistent? Than why oh why does everyone keep talking about it? That’s honestly a good question. So here’s the breakdown:

When you exercise, your body uses different substrates to create energy for your muscles to continue to contract (so that you don’t end up a heap of Ghostbusters Slime on the floor).Energy for your muscles comes first from carbohydrates and fats, and then in more dire times, from protein. The first and easiest source of energy for your working muscles are carbohydrates, which can be turned into energy rather quickly. However, the one downfall to this is that your body needs plenty of oxygen to convert glucose into energy, and when we do high intensity exercise — think hill sprints, sled pushes, heavy KB swings, sets of dreaded burpees– the body lacks enough oxygen to continue this energy making process.

So instead of just shutting down, since our bodies are wild and crazy machines that power through some of the most amazing circumstances, lactate is formed.  Essentially (without going into too much detail and losing all of you), during normal aerobic energy production, glucose is broken down to form pyruvate, which is then converted into energy through a series of steps that utilize oxygen. When oxygen isn’t available, however, pyruvate is converted into lactate. Lactate allows the glycogen breakdown and energy production to continue, even when you’re sucking wind and have very little oxygen on demand for your cells.

Lactate, commonly called “Lactic Acid” is then utilized during those periods of low oxygen. And I’m talking just a few minutes at a time here, not days upon days of some slime sitting inside of your muscles making you sore.

But, here’s the catch that most people don’t realize: once that period of low oxygen is over and the body recovers from that last sprint, sled push or set of burpees, lactate is shuttled out of cells, converted back into pyruvate and the oxygen utilizing process of energy production continues. Thus, lactate is almost immediately cleared from your muscles after a tough workout session; it is only there for the short time that your muscles absolutely need it for energy production. Once it’s need has passed (that is, once your high intensity bout has finished), the body gets rid of it rather quickly and efficiently. Essentially, lactate is an important form of fuel for your muscles, not the enemy. Converting that built up lactate into pyruvate allows your muscles to keep contracting (and your exercise session to continue).

So, lactic acid doesn’t build up in my muscles?

Well, yes and no. During those times of high intensity exercise — I’m talking short bouts of about 1-3 minutes here, lactate does build up in your muscle tissue. And it can build up to quite high levels –but your body will use this quite efficiency as fuel.

After that high intensity bout though, that lactate does not just hang around. It does not become comfortable, kick it’s shoes off, and crash on your bicep’s couch for a few days. It is just about immediately converted back into a usable form for your muscles, so that you don’t end up in a sweaty heap on the floor.

This cycle can happen over and over again, depending on your fitness level and “lactate threshold”, which is why we are able to do things like HIIT incline hill sprints, and still have legs to walk on afterward. The recovery period is key when training into your lactate zone, and is what allows you to do rep after rep of those torturous hill sprints.

So Why did You Say Lactic acid doesn’t exist?

Because it’s a misnomer, and one that people overuse in the fitness world. Yes, lactate is very important when training at high intensities for short bouts; it allows us to take our training to the next level. However, that’s all it is. Lactic acid is not a byproduct of lactate that hangs around and creates soreness, and in the fitness works, it’s simply a different name for lactate. That’s it.

Now, at times of high intensity exercise, your body produces lactate, while at the same time producing hydrogen ions (acid). When people refer to lactic acid, they are referring to this acid formation, however that assumption is incorrect. This acid does not stay with lactate, and therefore is not “lactic acid”. There is lactate (fuel for your working muscles) and acid — these are two seperate entities. That acid, along with other metabolites in your blood, contribute to the burning sensation during exercise. But again, this is not lactate or “lactic acid”.

Now, all of this being said, lactate is very important to training, especially if you are trying to improve performance, or perform at higher intensities for a longer period of time, as in cycling or running road races. Or heck, just squeezing out a couple more hill sprint reps. But training to improve your lactate threshold is a completely different post for a different time (and one that you can find a thousand articles about on the interwebs with a quick search).

The bottom line for this post is that I hope you understand one thing: lactic acid does not build up in your muscles long term and it is not what causes that crippling delayed onset muscle soreness after a tough gym session. And next time someone tells you otherwise, hopefully you’ll be prepared to let them know that any lactate that did form during your workout has cleared rather quickly on its own, thank you very much.

If you want to really sound like a smarty pants, you can even throw around some fancy words like pyruvate or glycolysis. Now go drop some knowledge bombs on those gym bros!

8 thoughts on “Fitness Myth Busting Part 1: Lactic Acid

  1. Yup I probably looked like the dog, but on read 2 it clicked! Thank you!


  2. Lactate is not another name for lactic acid. Lactate is the salt form of lactic acid. That burn one feels can be attributed to an increase in hydrogen ions (protons) but not to lactic acid. Also lactate can leave the muscle that produced it and diffuse into nearby muscle fibers where it can be lconverted to pyruvate and then enter the Krebs (citric acid) cycle to create more ATP.

    1. Hi Sam. You are correct– the chemistry is different between the two, strictly speaking. But when referred to in the fitness world, what most people are referring to as lactic acid is actually lactate. As the body produces lactate, it also produces the hydrogen ions you mention, but these do not stay with the lactate, hence it is not actually “lactic acid” production or build up. I meant to convey this but certainly misspoke. I have edited the original post to make my point more clear.

  3. I see the point and the usefulness of this article. It’s important for people to know that it’s not necessarily the intensity they are working at that causes muscle soreness.

    But like Sam says above, the physiology behind it is all wrong. Lactic acid and lactate are definitely not the same, and it is indeed acidosis from H+ ions that causes burning/contributes to fatigue.

    1. Hi Danny, thanks for your input. Please see my reply to the above comment.

  4. really informative post, Stephanie! I’ve definitely been guilty of using that phrase before- oops!!

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