#25 – What absorbs impact? Is it your cartilage? Your bones?

In today’s episode, Matt discusses the prevailing ideas of how our bodies absorb impact and how these ideas affect the decisions we make.

Article: Muscle as a molecular machine for protecting joints and bones by absorbing mechanical impacts


Hey, everybody! It’s Matt Hsu and welcome to Episode 25 of the Upright Health Podcast. Today’s episode is about Impact. Specifically, what absorbs impact? Is it your cartilage? Is it your bones? Or is it something else? Today’s topic comes about because I have been doing a bunch of research into orthopedic stuff recently. And this last week, I’ve been looking a lot more in to different kinds of studies on hip joint injections and the role of osteoarthritis in pain. And in doing so, I keep coming across a very familiar idea that I’m sure pretty much everybody listening to this has heard before.

And the idea is stated simply as this: Your ability to absorb impact and to go about your daily life, but really to absorb impact is based on the cartilage and the soft structures in your joints. So for example, you have probably heard somebody say, “Oh, my doctor said I wore through all the cartilage in my knees, so that’s why my knee hurts so much. So I need to stop running.” Or “I can’t play basketball anymore because I’ve done so much jumping that I’ve destroyed my labrum in my left hip, so I can’t handle the impact.” I think the most common version is the one with running. People are often told that “I ran too much and now I’ve worn out my knee. I’ve worn out my hip.” This is a really common thing that people say. It’s a very common thing people are told. But I think it’s based on a theory that lacks explanatory power. I don’t think this is a theory that makes sense and I want to talk about why.

There is actually this great little paper that was published (that I will link to) from a group of scientists. It’s called “Muscle as a molecular machine for protecting joints and bones by absorbing mechanical impacts.” So essentially, in this paper, they are talking about how muscle… they suspect muscle is a much, much, much more important factor in absorbing impact and is commonly accounted for in for the way we look at the human body. They got into a lot very interesting, wonky discussions. But I think one of the most easy-to-understand explanations that they have here that kind of shows the weaknesses of the argument of it’s just the cartilage or the meniscus or the labrum in your joints that’s doing the impact absorption is this one right here: “A trained athlete may easily jump down a height of over 3 m without damaging his knee joints. Suppose that the mass of that athlete who jumps down a 3 m height is 80 kg and the distance that his center of gravity travels from the moment he touches the ground till complete stop is 20 cm (due to bending of his knee joints). It is easy to estimate that the resulting force affecting his menisci, the cartilage pads between the weight bearing joint surfaces of the femur and the tibia, will be over 1,000 kg. The menisci may function as shock absorbers at moderate impacts such as those occurring during walking and running. But without major contributions of leg skeletal muscles to the shock absorption, the jumping down from 2-3 m height will hardly be possible.”

So this a very clear example. If you take somebody who’s well-trained and you have them jump off something high, they can be fine. Like a three-meter high is actually, for most of us, is a fairly frightening height. It’s like a little over nine feet. It’s a little under nine feet, actually. (laughs) Well, I’m displaying my ignorance right now about the metric system. I have not had to convert from feet to meters in a while. So for all my international listeners, I apologize. I do know that one kilograms 2.2 pounds, so there’s that. In any case, jumping from three meters, for most of us, is pretty scary. I personally remember just jumping down from four feet (which is just a little over a meter) used to be really, really scary and difficult. Not when I was younger. When I was younger and healthier, right up until I was about nineteen, it felt fine. No problem. But once I started getting different sports injuries and I started being more sedentary, things started to become more and more difficult to the point where walking down the stairs is getting hard. And then, by my early twenties and definitely in my mid-twenties, the idea of jumping off something that was even just you know, two-feet off the ground was very scary. And doing so actually felt really bad for my hip joints. I could feel my hips and also my knees just felt really, really unstable and unable to handle jumping off of things, right?

Now, the thing is with this trained athlete that they are referring to in this paper, this is somebody who has basically, gradually progressively made their body capable of doing that. So when you look at people like parkour athletes, these are people who… in case you’ve never heard of parkour, you should go on YouTube now and go check out some videos. It’s spelled p-a-r-k-o-u-r. There are some fantastic videos of people doing some amazingly frightening things — jumping off things that you wouldn’t believe they can jump off of. They are absorbing impacts that you literally will not believe they are able to absorb. And what you’ll notice though is they are absorbing it with their entire bodies. They are using the muscles and the coordination of those muscles to handle very high impacts in a very graceful way. They’re jumping, you know, huge distances horizontally and vertically and surviving. And not just surviving but making it look effortless. And it has to do with how their muscles are trained.

In the conventional notion of joint health, we talked about cartilage and we talked about the menisci, the labrum in your hip, those are all things that are generally understood to have no ability to regenerate and no ability to have their impact absorption capabilities improve. Once you tear a labrum it’s torn. Once you tear a meniscus, it’s torn. So if you were to say expose it to a force like say even, in this example, they said a thousand kilograms, right? If we said, “Hey, why don’t we expose it to just 300kg?” That’s probably enough to tear that soft little thing. So as you’re training, something else has to be helping you absorb and mitigate the impact. And it just simply cannot be these tiny little structures. Those things cannot heal. They cannot develop better. There has to be something that can be trained and trained in a fairly quick way. The only thing in our bodies that trains quick enough, that adapts quick enough to deal with that kind of challenge is muscle, right? Bone doesn’t remodel fast enough. And bone certainly does not compress enough to help you absorb that much impact, right? If bone were absorbing that impact, your bones would be super, super, super spongy, right? They would be… maybe not spongy. Spongy may not be the right word but “springy.” You should see them compress a ton and then expand back out – but they don’t do that. Neither do our knee joints or our hip joints. The only thing that’s happening is muscles are acting on the stiffer stuff. The muscles are acting on the bones and helping us absorb the impact of what we’re doing.

So this paper that I’m referring to also talks about muscle on the molecular level. I don’t have a full understanding of everything that’s being discussed. I hadn’t given it a full, thorough read. But it’s very interesting to know because they are noticing that there is a flaw in this idea, that it’s just these soft structures inside the joint that are absorbing impact. It’s simply not possible. So the question you might be asking, you know, how does that affect me? How does that affect the way I should be looking at my body? Well, if it’s the muscles that are helping you absorb impact, then it’s the muscles you should be looking at to figure out how you need to train them, so that you can continue to absorb impact in a healthy safe way. The conventional idea of “Oh, it’s just a cartilage in your joints. It’s just those soft little rubbery things – your labrum or your meniscus.” If those things are truly the only things that absorb impact, then your only option is to not use them. And that’s standard recommendation at this point.

You know, when I was younger and my knee is hurting, I was told, “Oh, you basically have used your knee too much.” And that was when I was 22. You know, that was not a satisfactory answer. It made no sense. There was literally no way I could have used my knee too much by the time I was 22. But that was, verbatim, the answer I was given when I asked, “Why does my knee hurt?” I was following an MRI, that was following a physical exam from a physician. And you know, the answer was, “Well, you’ve just used it too much. These things wear out.” That means, if you’re going to preserve your joints, you’re actually supposed to never move. And that means if you were to never move , your joints would stay in perfect health. And I don’t think you can show me many examples of people who don’t move much and have healthy joints after several years of not moving much. It simply does not happen.

Quite the opposite, it’s those who are moving in a healthy way and moving often and moving in the right amount, that actually have healthy joints. So what does that mean for you? If you move too little, your joints don’t feel so good. And if you move in a certain way too much, your joints also don’t feel good. So what could be mediating that process? Very likely muscles since muscle is pretty much the only tissue that is responsible for locomotion, for actual movement. And it’s the only tissue that can respond to stimuli that… at the same pace that you see people develop joint problems. So if I sit and do nothing for the next six months, I can guarantee my hips and my knees are not going to feel good. And it’s not going to be because of impact; it’s going to be because of the sedentary nature of my life and the fact that the muscles that are stabilizing those joints and protecting those joints are no longer functioning the way they should. And I can say that with a hundred percent certainty because I’ve already let myself of that once in my life. And I will probably never do it again.

So what that means for you now is take a look at this idea of cartilage and menisci and labrums being torn and of those things absorbing impact. Take a look at those things. See if they make sense to you. If they don’t make sense, then what’s the alternative? The alternative is that your muscles need to be addressed to help you move well. That doesn’t mean go out and run a marathon every day, right? Because you can also make muscles do things too much and those will also screw up joints. It means you have to find the balance. You have to find the right balance and understand what your body is supposed to feel like, how it’s supposed to move and what you should be able to reasonably expect from it.

I think for most people, you don’t have to have huge, crazy goals. But having reasonable goals of resiliency is really important. I have clients who have kids. I have clients who have grandkids. I don’t have any kids of my own at this point but I play with other people’s kids. And one of the things I’ve always kept in mind is if I’m going to have a kid, I want to be able to be the fun dad. And I want to be able to run around on the playground. I want to be able to jump off the slide. I want to be able to throw my kid up in the air, catch him and put him down and chase him. And run and jump and do all the things that the kid is doing so that, you know, the kid has a playmate and I’m able to enjoy that time. When I play with my nephew or niece, we’re running around climbing monkey bars. Doing things that, literally, for me, in my early and mid-twenties were impossible — physically impossible — because my body wasn’t trained for those activities. When I do them now, I don’t even have to think about them because I have gradually, gradually gotten my body to the point where it’s not an issue. And that’s what I hope you’ll start thinking about doing for yourself as well.

I just wanna close with this final quote here from the paper. So they say, “Numerous questions arise regarding the role of controlled muscle viscosity in the development of various diseases..” So that goes a little bit into the wonkier side of things but the next sentence is super important. “..Is the development of osteoporosis the only reason for the increased probability of bone fracture in elderly people? In addition to reduction of bone density, could a decrease in the effectiveness of the muscular impact defense system be responsible for broken bones?  Is a slowing brain, less able to direct muscular viscosity, also to blame? Could the improper use of muscles be one of the causes of joint diseases, such as tendonitis, bursitis and osteoarthritis, and could a joint problems be anticipated by monitoring muscle viscosity?” So in this paper, I should explain very quickly, they talk about muscle viscosity in terms of like how muscle thickness kind of affects its ability to help absorb impact, so that’s why they kept bringing that up. So they are actually looking at muscle as a shock absorber and looking at muscles as something that help your joints be healthy.

So these are ideas that are out there that I think are really important. I hope you seriously consider them. And I hope you remember then pain sucks, life shouldn’t.



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