Does Lactic Acid Really Cause Muscle Pain?

Does Lactic Acid Really Cause Muscle Pain?

[♪ INTRO] It’s one of those basic ideas you hear scientists
repeating all the time: correlation does not imply causation. Just because two things happened together
doesn’t mean one caused the other. Well, back in the 1920s, they ignored their
own advice. And the result was a major misconception that’s
still around today. Because, despite what you probably were taught
in high school, lactic acid does not make your muscles hurt when you exercise. In fact, it might actually help. It all started around 1920, with a German
biochemist named Otto Meyerhof. He helped figure out many of the steps of
glycolysis, which is the series of chemical reactions that cells use to make energy from
glucose — aka sugar. He also kind of fit the “mad scientist”
stereotype. If you’ve ever seen a scientist in a movie
electrifying disembodied frog legs, well, Meyerhof did that in real life. He took frog legs — just the leg parts — and
he gave them electric shocks, making them jump and twitch. But, after a while they stopped jumping, Meyerhof
found that the legs were full of lactic acid — or, more accurately, lactate, which is
lactic acid minus a proton. He and another scientist, Archibald Hill,
correctly figured out the steps of glycolysis that led to higher levels of lactate in the
muscles. But Meyerhof also assumed that the lactate
buildup contributed to muscle fatigue, stopping the frog legs from jumping around. When you exercise, your body uses up its main
source of energy, ATP, within a few seconds. Then it starts to make more, using a bunch
of different chemical reactions. And during a hard workout, your muscles start
to rely more heavily on reactions that also produce more lactate. When you exercise, the pH in your muscles
goes down, meaning they become more acidic. That’s called — appropriately — muscle
acidosis, and the drop in pH may be part of what causes the famous burn while you’re
exercising. There was a clear correlation between the lactate
buildup and acidity in the muscles, and Meyerhof assumed causation, too: that lactate was responsible
for lowering the PH in muscles. This became a generally accepted hypothesis,
and you still see it all over the place today. Unfortunately, as we all know, assuming causation
can be risky. And in this case, Meyerhof was wrong. Even though the lactate idea was well-accepted,
there wasn’t much empirical evidence for it, and over the years researchers started
to question whether it was accurate. Around the second half of the 20th century,
they started to pick apart what was really going on. One important clue was the fact that unlike
lactic acid, lactate isn’t an acid. That missing proton means it’s a base — it
accepts, rather than donates, protons. Meyerhof’s idea assumed the reaction that
produced lactate also produced a proton at the same time, making the muscles more acidic
overall. Turns out, it doesn’t. The series of reactions that generate more
ATP in muscles do produce extra protons, which lowers the pH in your muscles. But the extra protons don’t come from the
step that generates lactate. And, in fact, lactate bonds with some of those
protons, making the muscles less acidic. Lactate also isn’t involved in delayed onset
muscle soreness — the pain you feel a day or two after a hard workout. Scientists think that comes from microscopic
tears in your muscles, although they are still investigating that. It’s weird that we don’t 100% know, but
we don’t. So, despite what you hear from personal
trainers everywhere and sometimes even see in textbooks, there’s no reason to be so
hard on lactate. It’s just trying to help. Also, a side note here: you’re gonna want
to tell people about this. When they say “ah, the lactic acid!” Do it – but in the least pedantic way possible. We have to be accurate. But don’t be condescending! Thanks for asking this lovely question, and
thanks especially to our community on Patreon: your support keeps these answers coming! To learn more about how you can join — which
will also give you access to our quick questions inbox — just check out [♪ OUTRO]

100 Replies to “Does Lactic Acid Really Cause Muscle Pain?”

  1. Lactic acid doesn't make your muscles burn?!?! My AP Biology teacher lied to me!!! Huh, I wonder if I can get my high-school tuition back…

    Also, excuse me while I go apologize to my niece for lying to her about why her muscles hurt after Muy Thai…

  2. Sure we tell freshmen in stats 101 that correlation does not equal causation. They need it simple at first. But in fact it is a flag for further investigation. If you think otherwise then I invite you to take an advanced class – or talk to an investigator at CDC. That is a trope that grows tiresome and I wish it wasn't bandied about like a big club.

  3. I always thought the theory was that the burning feeling in your muscle as you work out was cause by lactic acid, not the pain days after. That once your limb had use up is oxygen supple for aerobic respiration then it started to produce lactic acid and doing so hurt but that you could push through the pain of it. Whether that pain was because its acid or not i never believed, just that your body didn't want you to keep doing that too much so naturally it makes us feel pain so we know we should probably stop.

  4. Okay, so why is that guy in (what I think is) Ireland so well adept at running, seemingly forever without lactic acid build up?

  5. I think a video on what we really DO know about how the body works, would be really useful. And it would be short. It would go something like “people who eat less seem to weigh less, and people who weigh less, seem to live longer. The rest is commentary. Also we have no real idea.”

  6. I just heard my uncle say my muscle soreness days after a workout was from lactic acid, "I didn't stretch afterwards, so it wasn't squeezed out."
    I just let him have that one. It's really hard to not sound condescending.

  7. Although yes correlatin is not causation there was strong evidence at the time for this. He didnt assume anything, by your logic everything is assumed to be causation and what do we aftually know than?

  8. Poorly constructed….. A quick demeaning description of Otto Meyerhof to workup to what sounds like a valid and reasonable test that would have been performed in the 1920's, all to get to the point that his work helped to correctly figure out the steps to glycolysis. Then, (I can only assume this part because your sources only show ((again what I can only assume, due to some of your sources needing to sign up to their sites to view the entire paper)) what appears to be papers that support your argument.) you speak of his assumptions (based on his previous experiments) and state that it became a "generally excepted hypothesis", yet you don't state if he conducted anymore experiments or research to prove or disprove his assumptions…..just that "Meyerhof was wrong".

    "The drop in pH may be part of what causes the famous burn while you're exercising" "In fact, it might actually help" These are direct quotes from your video, not only spoken but written to further drive the point, yet both are opinion statements….I dare say like an assumption.

    In the video you speak of "empirical evidence" and studies in the second half of the twentieth century, yet I could use a little more source material for this ( I say this only as a point of clarification, while the studies could have, and more than likely took place between 1950-2000 (second half of the twentieth century), your sources date 1921, 1933, 2004, 2008, 2010, 2017….

    One of the sources, that is able to be fully viewed, ( ) does give some interesting information about metabolic acidosis (I didn't see how it fit in with the video, but I will freely admit I only read the highlights being that its around 3a.m.). I should note that this link did have links to other corresponding topics …( )(Honestly don't know if it has anything to do with this topic either but I figured what the hell.)

    Sidebar to the main complaint of this video, around the 3:00 mark, "it's weird that we don't 100% know, but we don't"…..three things came to mind when you said that; 1) I think it is more weird that we don't 100% know why we have an appendix, 2) What experiments would you think about doing that would give use 100% knowledge on that, and 3) Do you think that there is 100% knowledge of any science out there???

    "We have to be accurate, but don't be condescending"…..Where in this video were you accurate? You made a few statements, but don't site reference. You have source material that will definitely make sure I get to sleep within a few pages of reading, yet don't do your viewers the service of referencing any of it. Not to be an ass (probably too late), but Meyerhof did get a Nobel Prize for his work, and without proper references, sources, or even general fact finding checks and balances you are just a guy in front of a camera. I watch this channel because you have interesting topics, but I feel the more videos I watch the more I have to fact check your opinions.

    ((This is just a personal critique of your write up, but I did find it curious you choose to add the modifier German, yet omitted such modifiers as Jewish or Nobel Prize winner…))

  9. Hahaha the tip at the end, you read my mind! I was wondering how to tell this to the other trainers when they bring it up, without sounding like captain gym douche…

  10. I've never thought that Lactic Acid caused muscle soreness, I was always told it was caused by tearing muscle fibers.

  11. Well actually …. i dont know how to correct people without that phrase, which is inherently condescending please help

  12. of course we don't know 100 % of our body, if you want to know you have to cut people legs after exercise and check it to lab which is human experiment hahahaha

  13. Hah I wish more people listened to the correlation does not equal causation thing. That would fix a lot of arguments that people have.

  14. THANK YOU HANK. Also, lactate is actually an important fuel source, as it is extremely similar to It's precursor, pyruvate.

  15. I had a guy at the gym tell me that the tingle in my ears hands etc from my preworkout was from lactic acid. And being a personal trainer i have known that was bs for a while but this guy was absolutely unwilling to accept that he was wrong.. (The tingling is from the diameter change of blood vessels and the nervous system being stimulated, both caused by various stimulants in the preworkout)
    Side note.. Pre workout is NOT healthy to take long term.. Most recommend taking it in cycles with off periods.. Mine is 8-10weeks on 8-10 weeks off… Be safe guys.. Only pain you want is muscle pain not liver and kidney!

  16. Somewhere, Muscle Hank is just curled up in a muscular ball, rocking and muttering, "My whole life has been a lie" over and over. EDIT: Also, I'd love to see a SciShow episode talking about protein shakes and other popular weightlifting supplements. Is there any science behind them? As an old guy trying to get back in shape, I'd love to know if any of that stuff actually does anything useful.

  17. "It's weird that we don't 100% know, but we don't" is maybe the most common phrase I say while teaching science to general audiences haha.

  18. Hank came through! Just got back from leg day and stairclimbers. It's too bad we still don't know what causes muscle soreness smh.

  19. About 20 years ago, I was about 13-14 years old when I was hospitalized for some injury on my left arm. I was working out a lot back then for reasons, and one day my arm just hurt like hell. The pain was so hardcore I just couldn't use it.
    Doctor's diagnosis was that most muscles on my arm were fractured due to the high amount of lactate.
    He told me something about the range of the concentration being 100-1000 and my blood test showed some 6 plus thousands.
    I have never thought about it much, but watching this video made me wonder;
    did he know what he was doing or is it possible I suffered the worst diet I've ever had just cause?

  20. It's hard to not come off as condescending to the kind of person who spreads disproved scientific "facts" about fitness because chances are they're doing that to show off how knowledgeable they are about fitness science! Luckily this is one of those "facts" that isn't likely to cause some unassuming novice any trouble so there isn't much need to correct (unlike them using bad form or advocating dangerous exercises).

  21. Some time ago i saw a program where they put an ultra-marathoner on a treadmill. This person does dawn to dusk runs for FUN! While on the treadmill they measured his lactate (acid?), and as he ran longer and longer the measurement went down!

  22. Calmly states that electric shocks caused fast twitches and movements that produce lactate and that lactate is good for you? maybe? Now looking at electrostatic to get a six pack.

  23. We were just learning that Lactic Acid causes muscle soreness in my college level Prevention and Treatment of Athletic Injuries class. Haha. I wonder what the best way is to show this video to my teacher…

  24. I need a gif of 3:28 : "We have to be accurate, but don't be condescending!" … And the sparkly text – I love it!
    Or even better mugs, Tshirts, EVERYTHING!

  25. lactate gets turned back into pyruvate which then gets turned into ATP again aye its a good thing and aye it took me a long long time to get this science right

  26. When u just give bio exam yesterday and wrote that lactic acid causes muscle pain because ur text book says so and THEN U WATCH THIS….

  27. If lactic acid is more acidic than lactate, why the video (at 3:00) says that the lactate bonds with some of the protons (so it becomes lactic acid), making the muscles LESS acidic ??? If it becomes lactic acid, it should be MORE acidic. Am I right ?
    (I don’t speak english perfectly because I’m belgian so maybe i just didn’t understand correctly)

    And what do y’all think ?

  28. But do mechanisms that reduce the build-up of lactic acid help here? Do they take lactate and one of the extra protons at the same time? I'm thinking of Michael Phelp's famed genetic advantage that means he processes lactic acid twice as fast as his competitors. Is this actually raising the pH (through removing additional free protons) or just getting rid of lactate (and so actually making the muscles more acidic)?

  29. does this mean that "lactic acid" isnt actually a thing. its just lactate(isnt an acid and never has been)…and the extra protons where just being blamed on them?! wtactualf

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