What Is Muscle Soreness? It Isn't Muscle Tears... | Dr. Andy Galpin & Dr. Andrew Huberman
00:00:00.000 | I do have a question about recovery and it's one that I think most people are familiar
00:00:06.220 | with themselves, which is soreness.
00:00:10.540 | We think of it as a muscle soreness, but I was trained early on in my scientific career
00:00:15.900 | to always question the seemingly obvious.
00:00:19.940 | So a couple of questions about soreness.
00:00:22.300 | First of all, what does soreness really reflect?
00:00:25.500 | Is it really muscle soreness?
00:00:28.500 | It feels like it's in the muscles, but what other organ systems and tissues and cell types
00:00:34.020 | does it involve?
00:00:35.580 | And then I'm particularly interested in this concept or this experience that many of us,
00:00:41.780 | including myself, had, which is delayed onset muscle soreness.
00:00:46.380 | Why would it be that when we are less in shape or when we perform a movement that is extremely
00:00:51.460 | novel to us, the soreness seems to arrive after a reasonable delay of maybe even a day.
00:00:58.660 | You know, we're fine the next day, but then 48 hours later, we are exceedingly sore.
00:01:03.180 | And as we get more fit or more familiar with the movement, the soreness seems to arrive
00:01:06.940 | earlier.
00:01:07.940 | So I realized I just asked you about three questions or more.
00:01:11.100 | First of all, what is muscle soreness at a cellular level, which cells, which organ systems
00:01:15.980 | and so forth?
00:01:17.460 | What does it mean if we are sore is something I know we'll get into a little bit later.
00:01:21.500 | And then why the delayed onset muscle soreness?
00:01:24.180 | It's actually one question.
00:01:25.740 | So it's totally fine.
00:01:26.740 | You answered all, you asked all three because I'm going to actually answer number three,
00:01:30.780 | which will answer number two, which will actually answer number one.
00:01:34.260 | I'd love to tell you that I set it up that way intentionally, but I'm just happy to hear
00:01:38.340 | that where I was unable to be concise, you are able to be concise.
00:01:41.900 | Thank you.
00:01:42.900 | Yeah.
00:01:43.900 | We are still learning a lot about this area.
00:01:45.560 | It's actually really difficult to perform these studies.
00:01:48.540 | Anytime you ask a question about something like pain or soreness, you're immediately
00:01:54.220 | talking about perception.
00:01:56.900 | And there is obviously a physical component to that, and there's also perception.
00:02:01.140 | And so teasing those things out is extraordinarily challenging.
00:02:04.020 | That said, there has been a lot of work in this area.
00:02:06.060 | And in fact, probably you may have a show already out on pain or maybe one's coming
00:02:10.580 | down the road.
00:02:11.660 | We did an episode on pain a while ago, but it's definitely time to revisit that literature.
00:02:17.480 | I also have some amazing colleagues at Stanford who work on pain, both from the cellular and
00:02:23.480 | molecular side, but also from the psychological side about how our understanding of pain and
00:02:29.520 | what we believe about pain shapes the experience of pain and pain relief.
00:02:33.400 | Amazing.
00:02:34.400 | That stuff is incredibly important, and I'm glad we flagged that, and maybe we'll just
00:02:37.760 | call that good for now.
00:02:38.760 | They can come back later for another one of your shows.
00:02:41.320 | So that being said, why does it happen 28 to 48 hours after you exercise?
00:02:47.960 | Well, that actually should give you some clues into what's happening.
00:02:51.520 | So the traditional dogma of delayed onset muscle soreness is what this is called, is
00:02:56.120 | that it is a result of "micro tears" in the muscle.
00:02:59.920 | And so you can sort of think, I challenged the muscle, there were some small tears in
00:03:03.760 | there and I'm feeling the results of that.
00:03:06.400 | Well, in fact, that certainly does happen, and it can happen.
00:03:11.680 | That is not what's explaining your muscle soreness, and in fact, you can be quite sore
00:03:17.200 | from exercise and have no measurable amount of muscle damage.
00:03:22.040 | And so much like anything else, when we're in this idea of pain, it's not a one-to-one
00:03:27.360 | explanation.
00:03:28.980 | There are multiple factors that are probably causing your perception of pain.
00:03:32.960 | Muscle damage can be one of them.
00:03:35.800 | It is not the only one, and it is probably, in my opinion, though this is yet to be shown
00:03:40.080 | definitively, probably not even the leading cause of it.
00:03:44.660 | And so what's actually happening?
00:03:45.760 | Well, the reason it's taking you 24 to 48 hours is you can actually find various papers,
00:03:51.320 | literature reviews dating back a number of years now, over a decade, that show these
00:03:55.400 | wonderful curves of an inflammatory and immune response, and we don't need to necessarily
00:04:01.000 | go through the entire physiology right now, but effectively what's happening is those
00:04:04.880 | things have a little bit of a time delay.
00:04:07.160 | And so some of those steps happen immediately, like right when the exercise is there, and
00:04:11.120 | then some of them are delayed 6 to 24 to 48 hours.
00:04:14.840 | If you know a little bit about this physiology, you have a combination of neutrophils and
00:04:19.520 | macrophages and a bunch of things happening, and this has a time sequence.
00:04:22.860 | So what happens is by the time we get to this 28 to 48-hour window, now the muscle soreness
00:04:28.500 | kicks in, which, wait a minute, if this was a result of my muscles being torn and that
00:04:34.640 | happened immediately, wouldn't that pain start immediately?
00:04:38.800 | Well, the answer is it would.
00:04:40.520 | And so that is your first clue that that's not responsible for it.
00:04:43.840 | When we look at that immune response and we see that that has actually peaked 24 to 48
00:04:47.640 | hours later, and then that's the same time the pain kicked in, that's calling you in
00:04:52.520 | at the problem.
00:04:53.520 | So we have this immune response happening in inflammation, then all of a sudden we start
00:04:56.360 | getting fluid accumulation, and now there are what are called nociceptors, and you're
00:05:01.060 | probably very, obviously you're very familiar with these, and these are your pain receptors.
00:05:04.620 | What's actually interesting is we don't necessarily know a lot of information about how many pain
00:05:09.340 | receptors are in muscle.
00:05:11.740 | They're not really in the belly.
00:05:12.740 | In fact, this is why I can perform my muscle biopsies and they don't really hurt.
00:05:16.040 | You mean in the belly of the muscle?
00:05:17.460 | Correct.
00:05:18.460 | Yeah.
00:05:19.460 | We do have pressure sensors though, and so if you change the volume of the tissue, you
00:05:22.680 | will respond to that very, very quickly.
00:05:24.300 | So by enhancing swelling in the actual muscle, that is immediately putting pressure on those
00:05:30.580 | pressure receptors, if you will.
00:05:33.300 | That's the signal.
00:05:34.300 | So what's probably happening here, and I just hate to give you another bone, but a lot of
00:05:39.260 | delayed on some muscle soreness is probably just a neural feedback loop rather than it
00:05:43.620 | is actual muscle damage.
00:05:44.620 | Yeah.
00:05:45.620 | It makes a lot of sense.
00:05:46.620 | There's a lot of interactions between the types of neurons that control touch sensation
00:05:53.540 | and pain sensation and itch sensation.
00:05:55.380 | In fact, a lot of people kind of collapse itch and pain together.
00:05:59.500 | Bingo.
00:06:00.500 | Yeah.
00:06:01.500 | You know, that something is painful and it itches is a familiar thing for people, mosquito
00:06:04.900 | bites and such.
00:06:07.020 | And of course, there's the classic gait theory of pain, which people will be familiar with
00:06:13.740 | and then I'll explain why I'm explaining this, which is if something hurts, you bonk your
00:06:20.140 | knee or you stub your toe.
00:06:21.780 | We tend to grab that body part and try and rub it totally.
00:06:25.460 | And that rubbing is not a coincidental thing.
00:06:28.260 | It activates a set of touch sensors that are that respond to kind of broad, dull touch.
00:06:36.860 | And that actively inhibits through the release of an inhibitory neurotransmitter, the fibers
00:06:42.860 | that control the pain signal.
00:06:44.560 | So anytime we rub a, you know, like a Charlie horse, our leg, or we, or we stub our toe
00:06:48.800 | and we, you know, we wince and then we grab the toe and we got like squeezing it a little
00:06:52.380 | bit, that's actually deactivating or partially inactivating the pain mechanism.
00:06:58.940 | So the idea that a swelling response would then trigger a neural response that then would
00:07:06.380 | recruit the pain receptor response here, I'm using broad, broad brush strokes here to explain
00:07:13.020 | this makes very good sense to me now.
00:07:16.580 | And only now that you've explained how this process works.
00:07:18.840 | I can actually even add more to that.
00:07:20.200 | So if you remember how muscles work, so we have to have some sort of signal from the
00:07:25.820 | nervous system that has to actually go in and tell the muscle to contract.
00:07:30.720 | Well, remember there a few episodes ago, we covered the physiology here of what's called
00:07:35.320 | a motor unit.
00:07:36.320 | Okay.
00:07:37.320 | Well, what I didn't explain to you are called muscle spindles.
00:07:40.920 | And we have talked about proprioception in an episode of before as well, but we never
00:07:45.300 | tied this picture together.
00:07:46.300 | So let me walk you through that really quickly.
00:07:48.180 | And it's going to tie this loop into a nice bow.
00:07:50.760 | So what happens is this motor unit is coming in from what's called an alpha motor unit.
00:07:58.440 | And that's going to be innervating your muscle fibers and that's going to tell the muscle
00:08:00.920 | fibers to contract.
00:08:02.580 | Those are typically spread out throughout the all sides of the muscle in interior, exterior
00:08:08.600 | all over.
00:08:09.600 | On the outside though, there is another type of muscle called a muscle spindle.
00:08:13.280 | Now these are non-contractile, so they don't have that actin and myosin and they don't
00:08:16.640 | produce force.
00:08:18.080 | They are responsive, they are proprioceptive.
00:08:20.920 | So what that means is they sense stretch.
00:08:23.680 | And this is why, for example, if you were to stretch a hamstring, stretch any muscle
00:08:28.200 | group, it doesn't really matter, or muscle, its innate response is to fire back to close
00:08:33.400 | that distance.
00:08:34.400 | And this is what keeps you from, say, if you're leaning to the right, you can imagine that
00:08:38.520 | the example we give is if you're standing on one foot and you start swaying to the right.
00:08:42.960 | All right, let's say you're standing on your right foot, and let's make this easier for
00:08:46.800 | folks.
00:08:47.800 | And you start swaying to the right, like you're going to fall on your right ear, will hit
00:08:51.040 | the ground.
00:08:52.280 | The inside of your right calf muscle will start being stretched.
00:08:56.280 | The outside will start being compressed, right?
00:08:59.000 | So the stretch on the inside of the right calf muscle will sense that stretch and it
00:09:03.400 | will respond by contracting.
00:09:04.880 | That pulls you back to the middle and stops you from falling.
00:09:08.500 | That's proprioception.
00:09:09.600 | And muscle spindles sense stretch and tell you to contract.
00:09:12.640 | The way that they work is through gamma motor neurons.
00:09:15.800 | And so these are sensory things.
00:09:17.000 | So what's happening is, unlike when you tell your muscle to contract, it goes alpha to
00:09:21.320 | the muscle, contract.
00:09:23.240 | These muscle spindles work such that it is, "Oh, I've been stretched," sends signal back
00:09:28.920 | to some central point, typically in the spinal cord, and we don't actually want to go all
00:09:32.680 | the way up to the brain.
00:09:33.680 | We've got a time delay.
00:09:35.080 | This is why these are subconscious, autonomic, right, versus somatic.
00:09:39.460 | So that gamma is going to go back to the central location and then come back through the alpha
00:09:43.500 | motor neurons and tell it to contract.
00:09:45.820 | So you have this wonderful mechanism of sensing stretch going back.
00:09:49.060 | Well, one theory that's been put forward regarding muscle damage is that the pressure is actually
00:09:56.700 | being applied to those nerve endings of the muscle spindles.
00:10:01.860 | And that's actually responsible for the pain signal that's going back and coming up to
00:10:06.400 | your brain and you're registering that as pain rather than it is actually in the contractile
00:10:10.360 | units, so the muscle fibers.
00:10:12.120 | That's a very intriguing idea because it would suggest that stretching muscles in order to
00:10:20.520 | alleviate soreness might be the exact incorrect thing to do.
00:10:25.200 | Yeah.
00:10:26.200 | Now, I'm not saying that's for certain.
00:10:27.680 | I'm just building off the mechanistic logic that we've laid out here.
00:10:31.980 | Yeah.
00:10:32.980 | Really that you've laid out here.
00:10:34.140 | There is a more effective principle based on exactly that, which is this is generally
00:10:38.700 | why low level movement is effective at reducing acute soreness.
00:10:43.340 | Because that's low level contraction of the muscles.
00:10:45.340 | And you're going to contract and get tissue out and get fluid out.
00:10:49.060 | Wow.
00:10:50.060 | You're literally pumping it out of the cell.
00:10:52.740 | Yes.
00:10:53.800 | In our previous episode where we were talking about programming or confusing the we, but
00:10:58.200 | let's be fair here, where you were educating us, including me and the audience about different
00:11:04.200 | structures for programming, exercise for specific adaptations, et cetera, the month, week, year
00:11:11.360 | scales, et cetera.
00:11:13.360 | We had a brief discussion about the fact that if one trains legs very hard with resistance
00:11:20.240 | training, some heavy squatting or dead lifting it, and there's some soreness that oftentimes
00:11:25.920 | doing some "lighter cardio" or some low impact work the next day or any number of different
00:11:34.080 | things that involve not high intensity contractions of the muscles, but that do require contractions
00:11:40.840 | of the muscles, that it can alleviate soreness more quickly than if one were to simply lie
00:11:45.700 | around and watch Netflix or something.
00:11:47.920 | Yeah, that's exactly right.
00:11:49.200 | The, to go back just a little bit as well, if that's really the case, the question is
00:11:55.400 | like, where is this inflammatory signal coming from?
00:11:59.120 | And while there's much to be learned there, there is a little bit of information right
00:12:05.400 | now that suggests it's potentially coming from free radicals released from the mitochondria.
00:12:10.240 | Again that may or may not hold up as more research comes, I'm not sure.
00:12:13.680 | But if you remember back to our conversation on endurance, so we talked about the electron
00:12:18.160 | transport chain and aerobic metabolism, regardless of whether or not you're getting energy from
00:12:22.440 | glycolysis or carbohydrates, remember they have to be finished through aerobic metabolism.
00:12:29.080 | So even if you're lifting weights and you're using carbs for your fuel, you have got to
00:12:34.600 | finish that metabolism by running it into the mitochondria and performing oxidative
00:12:38.320 | metabolism.
00:12:39.320 | As a result of that, that electron transport chain runs.
00:12:42.240 | So theoretically, if free radicals, which are hyperreactive oxygen species, basically
00:12:47.520 | they're oxygen molecules that are missing an electron so that they react to a lot of
00:12:51.480 | things.
00:12:52.480 | They're the opposite of antioxidants by the way, this is oxygen molecules with extra protons
00:12:57.600 | so they can balance the charge.
00:12:59.480 | If those leak out, that in and of itself is going to be a massive inflammatory signal
00:13:03.640 | and that's probably what signals the cause of these neutrophils and macrophages and kicks
00:13:07.740 | off this entire cascade.
00:13:09.680 | Again I believe we need more research there.
00:13:11.600 | I need to look into it, maybe it's more definitive than I know.
00:13:16.080 | But that's probably what's happening, potentially what's happening rather, that causes that
00:13:20.580 | cascade in signal.
00:13:22.520 | Also what you have is this combination of, well if that's the case, why am I not getting
00:13:28.720 | tremendous amount of muscle damage when I do more aerobic based exercise?
00:13:33.920 | Well because you don't have the mechanical tension pulling on the fibers that's actually
00:13:37.640 | causing damage to the cell wall that allows these free radicals to escape the mitochondria
00:13:43.360 | and the cell wall.
00:13:44.360 | It's the best we can postulate at this moment as to why those things are happening.
00:13:48.560 | And then why, again, low level exercise tends to enhance, even things like percussion.
00:13:55.200 | So using either instruments that put a low level of vibration into your leg or like pneumatic
00:14:00.520 | boots so you can massage, all these things are generally probably helping because they're
00:14:05.300 | moving that stuff out, edema most specifically, so pressure comes off of those nerve endings
00:14:12.160 | and the muscle spindles and allows you to stop receiving that signal of pain despite
00:14:17.040 | the fact that you didn't actually regenerate tissue at all yet.
00:14:20.400 | [Music]