In this Episode of the Handstandcast, Emmet and Mikael have a special guest: Dr. Helgi Freyr Rúnarsson, handbalancer and Dr. of Physics, to discuss the physics of the handstand. Going deep into detail about the difference between centre of mass and centre of gravity, the inverted pendulum and more, plus how these variables are important to understanding the handstand.
We hope you enjoy it!
S1E31 – Physics of the Handstand
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Transcript of Episode 31: Physics of the Handstand
EL: Hello, and welcome back to the Handstand Cast with me, Emmet Louis, and my cohost, Mikael Kristiansen. We have a very special show this evening, because we are joined by a guest, a good friend of ours. I’ll introduce him by his formal title of Dr Helgi Freyr Rúnarsson, from Iceland.
Mikael, how would you describe Helgi?
MK: That’s very clear actually. I would describe Helgi as the ultimate life form because he has several desirable traits. First of all, he has a PhD in physics. He can do a one arm handstand. He has a wife and three kids, and is able to somehow manage with this. And he doesn’t drink coffee. Take that in, for a good 10 seconds. Imagine where you would be without your cup of coffee. I know I sure as hell wouldn’t be any of those things.
So welcome, Helgi. Really nice to have you on.
EL: Helgi has been a good friend of ours for quite some time, so I’m excited to have you on.
MK: I forgot to say, he’s also level 100 in Path to Exile, and that is as fucked up as all the other things combined.
EL: So Helgi, why don’t you tell us a bit about yourself, what you do, and all these kinds of things, so people get an overview of how the ultimate life form functions, day to day?
HF: Well, you forgot to mention I’m from Iceland, so that already puts me in a very small pool of people. I’m a 33 year old from Iceland. You guys have said I have a physics PhD. I finished that in 2017 in Portugal, on black holes, namely scalar hair, whatever that means. I’m not going to go into it what black holes with hair actually means-
EL: What I want to know is, is there a black hole comb?
HF: Probably. Yeah, how far do I go back? I used to play football as a kid, that was how I got introduced to exercise and stuff. I got very injured around 16-17 and basically gave up all exercising and went into studying physics and playing video games, as Mikael mentioned, for about 10-12 years. I basically didn’t do anything else. I studied for 8-12 hours a day, and the rest was sleeping or playing video games.
When did I get in touch with you, Emmet?
EL: 2014 or 2015 maybe?
HF: Yeah I think ’14 was the time you helped me with my back bend. After this huge injury I didn’t move at all. Then I started exercising again via some random bootcamp class yoga stuff. I met you on Reddit I think in 2014, 2015. You were beta testing all your programs of back bending, head to toe, and stuff. It worked for me, so I said I’m not going to do yoga anymore. I’m going to do what this guy Emmet is doing. I started focusing on handstands.
That’s how I got to know Mikael. I think it’s funny because when I met you for the first time, Emmet, in Berlin, you had just come back from the workshop with Mikael when you were meeting him for the first time. I think it was a week or two later.
Then I somehow transitioned from training with you to training with Mikael-
EL: “I don’t really want to train flexibility or strength or conditioning; I just want to do handstands so I’m going to train with Mikael.” I was like, have fun, off you go.
HF: I didn’t know Mikael played Path of Exile. I would have left a long time before if I’d known that.
MK: The first time I came to Iceland we were sitting there, talking. I was teaching a workshop in Iceland the first time I met Helgi. We go to his place and drive quite a long way from the airport. We were speaking about enthusiasm or something. I said I was so hyped for this new patch for this new game. He said, wait a second, what game is that? It’s this obscure small indie company from New Zealand, called Path of Exile. He said, do you play that? Then he slams my face with all these obscure builds and solutions I’d never heard of, like shit, this guy knows what he’s talking about.
EL: What you’re getting is a glimpse of our conversation when these two are around. I don’t play Path of Exile. They’ve been trying to make me play but I’ve been holding off since it’s not the type of game I like. It’s just obscure builds and running maps, staying up to 5am to run maps when they should be sleeping.
MK: Yeah, so why are you with us today?
HF: It’s not for sure…but what it could be is we were going to talk about some physics related stuff in relation to the handstand.
I don’t even remember the first conversation me and Emmet had about it. Since I’m a physicist and Emmet technically did some time in th physics department-
EL: Have not got my doctorate, but spent some time
HF: The idea is to go through in a physics sense, what it means to balance on your hands, stuff about levers, basically any questions you guys have.
EL: There’s some stuff I’ve been brushing up on the last couple of weeks leading up to this. It’s a very interesting topic. One of the things I realized is the terminology – and we’re partly responsible because we use a very dumbed down terminology – it’s not actually what’s going on.
It’s like most examples in most maths and physics stuff: we use a simplified thing just so you grasp the idea, but that’s not really it. Ignore friction, because it doesn’t exist in the model, but it does in the real world.
MK: The first thing that strikes me then, the most talked about thing in handstand: the line. I mean that is a phenomenon of physics that does not express as it seems it might when looking intuitively at the body line and imagining everything is stacked on top of each other. That must make it easier, like if you stack bricks on top of each other they will stay more nicely in one configuration than another, but there are differences between static objects and our fluid filled bodies.
HF: For sure, the thing people think about the first time when they hear a straight line in a handstand is especially in a mathematics or physics kind of sense is, everything should be 180º. Your hips should be fully extended to 180º, your knees, ankles, shoulders, and that will make you hold a straight line.
As you guys have talked about in the podcast, that is not strictly true. What you call the mechanical line, Mikael – that’s not the definition of that, but people seem to aim for that. That is what straight means in this mathematical sense. People latch onto that and it’s a part of the confusion. People think straight in the math sense, while straight can mean something completely different, in terms of balance.
EL: Could you explain for people the difference between the centre of mass and the centre of gravity?
HF: The official difference?
EL: What I understand, the physics understanding, is the centre of mass is basically a fixed location in the object where the mass coincides. The centre of gravity, if we were to break your body into individual points and project a line from that point to the centre of the next gravitational body – correct me if I’m wrong now – that would be the centre of the earth for all intents and purposes here. You would do an equation that would sum up the locations of all these points and find out where they all coincide, or where their cumulative centre is.
This can move around. The way we deform the body, it can even be outside the body.
HF: It’s this idea that, and you might remember this, when we’re talking in physics, especially in Newtonian physics, we talk a lot about point masses. We say we can model a body that has a mass by one point. We don’t actually need to know its shape, just its centre.
Kepler derived his laws of planetary motion. He’s not considering the sun is made up of a lot of atoms. It’s just a point mass at a certain distance. Because those objects are basically spherical, with some small deformations, the centre of mass and centre of gravity are in the same place. They aren’t deformed.
For the human body, you can say the centre of mass…not quoting you Mikael, but you say this very often: it’s around your navel, slightly beneath your navel. But as soon as you pike, or do something else, your centre of gravity will go outside your body. Which doesn’t make any sense if you actually think about it. If you’re thinking about centre of mass, centre of mass isn’t the same as centre of gravity.
Centre of gravity is like, if you would model your complicated structure as a point object and how gravity affects it, that’s the point where it would be, in a sense. Obviously it’s very hard to calculate anything with a concrete shape.
The only thing I knew I was going to say on this podcast is this thing I was told while I was studying. It’s a story about how physicists work. Physicists in the UK were asked to calculate greenhouse gas emissions from cows in the UK, or something. They wrote a huge paper on it, I don’t know how many pages. It started with, “The assumptions of this paper are that we have cows that are spherical, in a vacuum.” Because it simplifies everything. They somehow stimulated or did something for the process of greenhouse emissions. It helped that they would be spherical in a vacuum. It’s the same thing you have to do for almost everything. You have to make some simplifications so you can actually do math. That is almost a problem of physics.
A lot of things we do have to be very idealized, in the sense that they don’t really represent anything in the physical world anymore. They will still get this pretty good idea of how things work.
EL: Black holes don’t actually have hair.
HF: They can, but the hair I was studying doesn’t describe any physical particles.
MK: Essentially a wig then.
What it made me think Helgi, and I’ve always been wondering so I’m happy to get it cleared up and have a useful distinction between centre of mass and centre of gravity. I’ve even heard the terms thrown around interchangeably, or that centre of gravity doesn’t exist as a term. Obviously it does. What it makes me think, as a random thought – obviously I am aware when you’re doing a pike handstand or Figa, that point will be outside your body. That centre of mass point.
The interesting feeling when doing that, and I’m sure both of you can easily relate to this, when you do a good pike, and that point is above your hands, or the middle of your hands. You never feel you need to go excessively over your fingers. That point is not moving over your fingers even though your ass is technically past your finger point. This is a thing I’ve been demonstrating as well, with the fingerless press, fingerless pike handstand, and so on. It never actually moves outside.
If you move your shoulders forward excessively in the same type of pike, then you’re actually moving that point forwards, putting more pressure and strain over your wrists.
HF: Just to reiterate the point of how physicists work, if you go to Wikipedia and type in ‘centre of gravity,’ which is found in a subsection of the article for ‘centre of mass,’ it starts with, “The center of gravity of a body is the point around which the resultant torque due to gravity forces vanishes.”
It doesn’t really tell you anything about how it actually works. It’s also a problem because….
EL: It’s too complicated, let’s leave it as an exercise to the reader.
MK: I have a concrete question. I remember I asked you this in the lead up to us doing this podcast. In terms of…since for a lot of our listeners, a lot of the lingo is abstract and obscure. One thing I’ve been thinking a lot about is how to define our various body parts in a handstand, like in a straddles and even more in a one arm handstand, and so on.
I asked you about a specific term. I can’t remember what I was using, maybe talking about the radius of a circle. You called it a lever. From my understanding, the lever is a useful term for determining the extremities of the body, ish? Am I correct?
HF: Basically the lever is describing not just the length away from the centre of your body, which is what the length or radius would imply. The lever is actually telling you it’s applying more force, more torque, due to the length of the lever. It describes the difference between a tuck, a diamond, or a straddle. Then you’re putting more mass further away from your centre, basically. It creates a larger level.
The easiest way to describe it is a see-saw. If it’s very short it’s going to have different forces than a see-saw that is very long. If a fat kid sits on the end of a see-saw, and a light kid on the other end, there’s a very different force at play. Most kids will do this, if you watch kids in kindergarten, you can still balance it by moving the kids to a different part of the see-saw, to have the same amount of torque on the see-saw.
That’s kind of the idea and why we call it a lever and not just the length. Obviously the lever has a length that plays a huge role. Also it’s the mass on the lever.
EL: Here’s an interesting thing on the modelling side of these things. Because our legs have mass at every individual segment, imagine if we slice it into slices, each bit of that acts on the length of a lever.
If you imagine a kid and a plank, and the weight is inconsistent with the weight of the kid at the other end, you get a leverage force. It kind of goes to this point with the levers, and, say, the straddle and the changing of the centre of mass. Is there any way we could calculate that meaningfully?
MK: Swing your legs into a vacuum?
EL: Yeah. We start with a circular hand balancer and a vacuum, with completely uniform thickness legs, of length L on each side. Can we work up, if the legs are overhead, how high that raises the centre of mass, compared to being in a full straddle, at a perfect 180º?
HF: You can calculate it. We talked about this a bit. I looked at it, especially for straddle because it’s the easiest case. The problem with physics, again, is you always have to make assumptions. The first one you have to make with something like this is the upper body, so from your hips and then down to your fingers in a handstand, remains absolutely still. It has to. You’re doing an open straddle, no pike, is the assumption I did. Then it’s very simple. The centre of mass of your legs is reduced by the cosine of half the angle of your straddle, or something. Cosine of an angle goes between 0 and 1.
You can reduce the centre of mass of your legs – not the whole body, obviously. The thing is the centre of mass of your whole body is a combination of these two things. It’s very simple; if you just google centre of mass, I think one of the first images is the centre of mass of two point objects.
The assumption you have to make is your upper body is one point object, the lower body is the other point object. The upper body doesn’t change, so the centre of mass of your lower body will then lower a bit, which will lower the total a tiny bit.
It’s very hard to say, “You straddled 45º, therefore it’s lowered y 10cm.” It obviously depends on the weight ratios of upper and lower body. There are some relations, but they’re all intuitive, I guess, in a sense.
If your legs are light, then your centre of mass will not move as much.
EL: If the legs are longer, would the centre of mass move more?
HF: No, technically not, because it’s only the angle between the legs that matters.
EL: Ahhh, interesting.
HF: Assuming fixed weight. The weight is always going to be the biggest part.
MK: If you would want to calculate the weight per cm of a leg, things would start getting really complicated, I would assume.
EL: I don’t know, you could get a meat slicer and do it.
HF: You can technically do it, and we looked at some papers before about weight distribution through the body. A lot of our weight of our body is in the trunk, so the centre of mass…it’s moving something. You can easily plug in some numbers and see for so and so tall person, it will move so and so cm. It will obviously depend on the person’s straddles and stuff.
What I find interesting is a deep tuck can lower it even more. You can get your knees below your hip line. That’s the thing; you have to pike your hips.
MK: The equivalent of a deep tuck would be a press to handstand, angle wise.
HF: Basically. The thing too, is the lever almost stops mattering since you’re on two arms. They always balance each other out. A diamond and straddle doesn’t change any forces to the side because they balance each other out.
MK: As we all know, the practicality of standing on your hands becomes drastically more complicated when you take away an arm. I guess we’re going to get into that as we roll on in the discussion. A lot more forces apply, things I don’t understand.
What I find interesting is, let’s say we continue down from the deep tuck, or let’s now say we’re going from handstand and legs straddle and start going into press to handstand. At some point, the legs are passing inside the line of the arms. You’re essentially starting a stalder negative press. You’re starting to approach the straddle L position.
What I have understood from my purely intuitive understanding, when you’re sitting in a straddle, your centre of gravity is somewhere around your sternum. As you’re going down deep enough, when you lower down you either stay with the hips extended and you planche, leading to that massive angle. If you pike a lot you reduce that angle so significantly. There’s a point where you go so significantly forwards that the legs come inside your arms and start counter balancing your ass, and so on.
What I found with straddle L, and the reason I mention this is there’s a spotting technique I use for straddle L. I think I used it on you Helgi when you start in the straddle L and I grab the sternum rather than the hips in the beginning. It seems to make sense to help the person from where their actual centre resides, rather than pulling the hip, at that point.
It does seem that since you’re so compressed, your centre actually goes up a significant amount.
HF: Yeah. If we think about it from the other direction, when you’re standing on your feet, where is your centre of mass or gravity? It’s around your navel. Now you’ve moved your legs to your hip level. That means your centre of mass or gravity will go up.
It’s definitely going to be higher than your hips. Is it at the sternum? I don’t know; it depends on every person. How much do they flex their spine? How high can they push the floor away? All that stuff. How high do they actively pancake? It’s definitely higher-
EL: It will probably come farther forward as well when piking at the hip.
HF: That’s the thing. That helps as well, now it’s a bit forwards. What people usually do is grab behind your thighs, under your thighs, almost over your head. This means you’re grabbing super far away from this point.
If you’re grabbing the sternum and around the ribs, then you are kind of lifting that point. If that point lifts, you can maneuver the legs better.
You’re lifting people.
MK: If you grab behind the thighs and pull, you’re going to be applying forwards force as well. Unless you block their knees, you’re literally sending them into a forwards roll. There’s no way your forearms and fingers can handle that much extra force when your shoulders are already front.
EL: That way of spotting the shoulders is the worst thing I’ve ever seen.
MK: It doesn’t seem to do much. I’ve seen people do 10-15 reps of spotted ones of those. Are we talking for very long periods of time in circus school, then you ask them to do a slow lower down, and they collapse around when the feet have come inside the arms. This is very evident to me, and it isn’t one person. I’ve seen at least 4-5 cases. It does seem to be you’re not getting to do that work. Shoulders are being blocked and you’re being pulled away from your centre, rather than ‘manoeuvre’ around the centre.
HF: I think especially the lower down to straddle like you were describing, or straddle L sit, it’s a nice way of thinking about lever stuff. As you said, the better your pike and the better your pancake, the less you have to lean. If you’re not piking properly, your lever out to the sides of the legs is going to be longer.
The legs still weigh the same, but since they’re further to the side, something has to counter balance the other side, creating a larger lever on that side.
MK: I got this mental image in my head of things I’ve seen several times: someone stands in a handstand. They go pike handstand and start lowering towards the floor. Instead of getting their legs close to their body, the legs stop quite far away. Then as they’re going to go into the straddle L, it looks as if they do this large swing into the L sit, I mean, so it becomes a large swing into the L-sit. If done to a straddle L, you usually fall into your ass and backwards. You end up as in some kind of bad parallel bar swing at the bottom, where your ass rocks back and forth.
You’d have to have lots more of that planche strength to deal with a lever that is further out.
EL: I’ve got a question, or an explanation for people. Can you explain to people what an inverted pendulum is, and how you balance one, and how it relates to human bodies?
HF: Sure. An inverted pendulum is literally what it sounds like; a pendulum that is upside down. I love it because, again, this is such a physics thing when you think about this problem.
The pendulum is the first harmonic oscillator that physicists learn about. It’s a nice way of saying it’s a solvable problem, a differential equation that describes the motion of a thing.
Basically everything in quantum mechanics is usually reduced down to a harmonic oscillator. It’s one of the first things people learn about in physics and you’re going to be using this for the next 20 years, if you’re a physicist.
It’s completely true. We try to reduce everything to a harmonic oscillator. You learn about this in the pendulum. It’s all pendulums, all the way down: vibration of atoms….but it’s very funny how they describe the inverted pendulum.
Yeah, it’s just like a pendulum, but gravity is inversed.
HF: If you think about it, you take a pendulum, it’s fixed at the top and swinging at the bottom. Okay now imagine gravity is now not going down but up. Okay now it’s an inverted pendulum.
The equations that describe it are basically the same as a normal pendulum. There’s just a minus sign.
Then you can solve those differential equations, and you will see they give you four ways to balance an inverted pendulum, which they describe as moving the pivot point.
The pivot point is basically the point where it’s fixed at the bottom. If we think about handstands, it’s essentially walking on your hands. It isn’t really balancing it, if we think about it. It still describes it in that way.
You can find this on YouTube and everywhere, if you type in ‘balancing’ and ‘inverted pendulum,’ you will see small robots balancing wine glasses on big sticks, or something, driving back and forth. They do these super well.
MK: That’s basically how you balance on the rings, too. You move the ring underneath you constantly.
HF: Hand to hand, it’s very, yeah.
Then you can basically apply torque at the pivot point, which is what we do, as hand balancers. It’s using your wrists and fingers and forearms to apply torque at the pivot point so you do not fall. Problem with us is obviously we can only apply torque in one direction with our hands.
Then comes the third one, which again is physic speak: changing the rate of rotation of a mass mounted on a pendulum, on an axis parallel to the pivot axis.
EL: Makes total sense, I do that all the time in my handstands.
HF: It’s basically saying the pendulum is rotating, as in it’s swinging back and forth, or something. You apply a force that is perpendicular to the axis of the pendulum. You move a mass on the pendulum either to the left or right, which is: piking your hips, closing your shoulders, bending your knees.
You’re moving a mass to the left or the right in order to balance. Again, just like balancing a handstand.
The last one, and maybe you don’t think about it that way, but you oscillate the pivot point up and down. You take the bottom of the pendulum and you move it up and down. It’s kind of what a lot of beginners do, at least in what I see. They will continuously drop their shoulders, elevate their shoulders. You see this in people who can’t hold their elevation. They go up and down, up and down, up and down. Then they’ve changed their pivot point from their hands to the shoulders. It’s called Kapitza’s Pendulum, probably a Russian physicist.
MK: This is like when you do strange experiments where you shake something and it stays upright, yeah?
HF: Yeah. You get like a drill saw… You basically tie a stick to a drill saw and make it punch up and down really fast, and you can balance a stick upside down that way.
This is again, from circus – I’ve seen you do this Emmet, with a bundle of sticks, holding them in your hand and balancing them. Obviously you move them back and forwards, but sometimes also up and down.
But, I have one more thing to say. I think this is the best thing. We were talking about doing this podcast and I went into research mode and looked at this, and thought this makes perfect sense for the handstand. The four ways to balance the inverted pendulum: it’s just like the handstand ! Oh my god, this is just the same.
Then at the bottom for the Wikipedia article for the pendulum, it says, “types of inverted pendulum.” It basically says, arguably the most prevalent example of a stable inverted pendulum is a human being. On our feet, everything I just said about a handstand also applies.
Going back to one of your first YouTube videos, Emmet, on using your hands as feet. It’s the same. Which is great though, it means we’re on the right path.
EL: It’s interesting you’ve basically described in physics terms. Now we’re missing one kind of thing related to the one arm handstand, which I’ll talk about in a second.
We’ve basically described, in physics terms, all the strategies you see how people balance and how they occur. There’s one thing I want to do some nerd math on. You have to correct me if I’m right or wrong, as it leads into something else.
I can remember when you’re working out the physics of a simple pendulum or simple harmonic motion that when you are calculating small angle swings of less than 15º, because sin 15º is negligible, it doesn’t translate to…. Maybe if we start exceeding 15º of balance correction, that’s when we need to actually do one of these line break corrections, or stepping.
You could probably figure out- we have a model in one of our programs, I think in Push Harder. We’re talking about the type of correction you’ll need to do relative to your stability. If you’re super balanced the corrections are just happening at the finger levers, since that applies leverage to the centre of mass.
As you lean farther forwards, your options are either to apply more force – but if you exceed the force you can’t, or if your line of gravity gets too close to the edge, then you have to do a line break.
I’m wondering, if it gets to 15º – is it every 15º, the horizontal force…?
HF: I’m going to refresh your memory. It’s basically because you can, in mathematics, do something called a Taylor series expansion of any function. Basically the thing is, it means you can take the function, like the Sin of something, and expand it into what’s called a power series.
If you had Sin of some angle, the power series is the angle to the power of 0, plus angle of power 1, angle of power of 2, with some coefficients in front.
This means that if the angle is very small, the angle to the power of 2 is also very small. The angle to the power of 3 is even smaller. For small angles, the sin of something is very small.
You can skip the rest of the series. You can basically say for small angles, the sin of an angle is equal to an angle. That is the assumption people can make.
I’m not sure if it translates over to corrections and which ones you would be using. I think that’s more to do with how much torque can you generate at your hands. Imagine building a pendulum that has a motor at the pivot point that can generate infinite force. Then it can technically rebalance itself from any angle.
The problem is we can’t.
MK: I’ve heard these terms before and discussed it a bit with Emmet. This is a bit of a tangent, but I don’t have any balance memories. I just go up and do things. You don’t need to remember how to bike, so it’s weird to think back on the response mechanisms. When I do various things, they involve all of these possibly, several times per second. Except the one where I don’t actually move my hand underneath myself, so that one is excluded, unless I walk or hop on my hands.
Even that, I remember when I do a lot of switches, I often have this response where I jump to my left hand and am off and am going to fall. I have weight for a split second, so I push and go back to the other hand and re-establish. I wasn’t actually in balance. I’ll just sort it out by pushing off, travelling force to other side, and re-establishing. All these things, in terms of the inverted pendulum, will be applied at any given moment.
It’s also very interesting as you said that the levers have very little to do in a two arm handstand. The lateral forces are virtually negligible. If you were a hand balancer in a vacuum, you would be opening your legs at exactly the same time to the exact same speed. Even in practice, the differential between that opening will be negligible since your balancing system and muscles are quite fast and strong.
HF: The thing with Emmet’s question from before is you could calculate relatively simply how much you’re able to produce with your fingers, just by doing a handstand on a scale and pushing down with your fingers. You pulse on a scale, basically.
MK: We have some scale experiments in the works.
HF: You could calculate the maximum angle you could save yourself from. Is that relevant? I don’t know. But you could do it.
If you think about it as your body remaining in a straight line as you’re falling over, when can you not save yourself? When do you have to do something other than pushing with your fingers? There might be some general-ish rule.
Clearly you guys have taught a lot of people. There is a breaking point for most people, no matter how strong you are in your finger. It seems to be about the same place once people have trained it. It’s more related to how tall you are, how heavy you are, and how strong you are in your fingers.
MK: I remember this guy in Australia was fucking stacked, an enormous man – a muscle monster. He must have been nearly 2m. He had great shoulders, super great mobility.
EL: Was it Thor?
MK: Not that Thor. Everyone was like damn, he should be able to handstand because he’s so strong and mobile and had good technique. He just couldn’t. I took a look at the guy and had him try toe pulls.
It was really obvious that with the amount of force he would have to produce in his hand to be able to balance, it would actually take him work. He was bodybuilder sized everywhere and was extremely tall. Obviously that equates to literally taking more hand work than 95% of people.
HF: There’s one thing to wrap up the inverted pendulums, to quote Wikipedia like I’ve been doing. They basically write down the placement acceleration from the central position, in terms of the length and gravitational exploration, and the initial displacement.
They basically say if you lean to the right by 1º, this is how fast you will start to accelerate to the right. It’s basically the idea of the equation. The equation says this acceleration is inversely proportional to the length of the pendulum.
Which means….tall pendulums fall more slowly than short ones. Throughout this whole thing of bodyweight fitness and everything, it’s always ‘it’s harder to be tall when doing bodyweight stuff, because the levers are longer.’ But in the case of the straight handstand you actually fall more slowly.
EL: But you require more force to save yourself, so you basically have a slower fall….you feel you’re falling but can’t save yourself because your fingers are too weak.
HF: It’s obviously a tongue in cheek thing I want to put out there, because I’m not tall.
EL: I have a question that I just thought of and have not mentally prepared over the last week or two.
I was wondering if we could talk about rotation in the one arm handstand, and how we can transfer the moment of inertia and the length of the lever, and how that actually speeds up the rate of rotation.
HF: Basically when things are rotating, in physics terms, it’s described by something called the angular momentum. This is because the rotational equivalent of momentum, which people kind of know what it is, though they wouldn’t be able to give you a definition. They do realize what momentum is.
It’s a bit more complicated when rotating. There’s a simple equation; it has to do with something called a moment of inertia and the angular speed. The angular speed is basically how fast you move, either degrees per second or radiance per second.
The moment of inertia is very similar to momentum. Angle of momentum is very similar to normal momentum, or linear momentum, in the sense that it’s some kind of mass or inertia, times some kind of speed or velocity.
The moment of inertia is obviously tied to the mass of the object, but also its shape, levers and everything. You can calculate the moment of inertia for a lot of things; a sphere, a cylinder, just a thin lever, a lot of things. What you basically find is the further the mass is displaced from the axis of rotation, the more moment of inertia it is. This means it’s going to slow it down, which most people kind of know.
There’s a lot of playground toys that exploit this thing. I actually have this right outside my house. My kids play on it. It’s basically a stick coming out of the ground, on platform that spins. The kids will go on it, and kicking the ground next to it, and spinning very fast. They will shoot either out a leg or arm, and that will slow it down. Then they pull it in and they start spinning faster.
I’ve seen hand balancing arms on two arms that do this. It’s very clear when they’re doing it. They go up, start spinning, usually starting in a straddle, then a tuck, then extend one leg to straight, then both to straight, and keeps spinning faster and faster and faster.
Even though there’s friction in the actual spinning table, it doesn’t matter because it’s changing the moment of inertia by deforming the shape.
EL: There’s an interesting video we’ll put into the notes for people to check out. If you think of the difference between a straight one arm handstand and a straddle one arm handstand. You think of the rate of rotation being one of the things Mikael’s been working to get into the public consciousness. When you feel stable on two arms and are doing a four finger support or something like this in a straight handstand, it feels stable because it’s rotating so fast you can’t feel the rotation.
I can think in the video about when he puts his legs together when going fast, basically the rate of rotation almost triples or quadruples.
HF: People will probably know this example more. Look at a figure skater, what do they do? Or a head spin or any spinning moment. My physics teacher in high school did this with us. He brought dumbbells to class and would go on his chair that could spin and start spinning. Then he’d extend his arms with a couple kg dumbbells in each arm, and slow down. Then he’d pull it in and speed up again.
By the way, he was like 75. Basically why this happens Is because this angular momentum quantity is a conserved quantity in a closed system, in the sense it doesn’t actually change.
Angular momentum is the product of the moment of inertia and angle of velocity. That product has to be the same number no matter what the moment of inertia is.
If you decrease the moment of inertia, the speed has to increase. If you increase the moment of inertia, the speed has to decrease. Basically two numbers have to equal the same when you multiply them together. If you change one, the other has to change in the opposite direction. That’s basically what is happening.
Why is conservation of angular momentum a thing? We would need a new podcast for that.
MK: It’s very obvious also, if we apply it directly to a one arm handstand, and the classical difference between how much harder a straddle one arm and legs together one arm is. Helgi can actually do a legs together one arm, and you know how much longer it took you to get that from the point of being able to do the straddle. That is the thing. You will see it even among professional hand balancers. If they do a legs together one arm and something goes south, the first thing they will do is open the legs. What is it, increasing the moment of inertia, is that the correct term?
HF: Yep, which in turn, because of conservation of angular momentum, will decrease the angle of velocity.
MK: As this happens, and like Emmet said, when people are learning, they often say, in straddle I rotate. How do you fix rotation?
The idea I get is the reason you are speaking about rotation in a straddle is because you actually feel it happening. It goes slow, you feel it and fall out as it happens.
With legs together, you might be in straight arm support and everything is fine. You take off your hand and fall, but don’t feel any rotation. It happens so quickly that you’re destabilized immediately.
HF: It’s also going to back to the levers. In a straight handstand it’s very short, basically the thickness of your thighs that is your cylinder that is rotating. It’s not going to move very fast, even though it’s rotating fast. It’s more its rotation in the angular velocity sense, more radiance per second.
In a straddle handstand, now you’ve extended your legs to the side, I don’t know how many – a metre or something, depending on how tall you are. Your foot is going to move faster in metres per second, but not in radiance per second. Its angular velocity is slower, but it feels faster because it technically is in a spacial sense. The rotation is still less.
Let’s put it this way. In a straight handstand compared to a straddle, your butt cheeks are rotating faster in a straight one. They’re in the same place. But your legs are in a different place.
Your torso will rotate slower in a straddle, that’s kind of the idea.
EL: That makes sense. If you think of the example a physics teacher gave; if you have two ants, and one of them is walking around the centre of the pizza, and the other is walking around the outside of the pizza. They have to finish at the same time. The one on the outside has to go super fast, even though they’re still rotating at the same time. So.
HF: It’s the same thing. The rotation in a straight is going to be faster because the moment of inertia is smaller. But the feeling…you don’t feel that kind of rotation as much in your body. You feel that in the straddle, oh my god, my legs move to the front or back. That’s what you feel. But you…you do later. I can say when I do a bad set up of a straight one arm now, I feel that I am rotating. It took me a year to start feeling, compared to straddle.
MK: There’s one example, a little physics experiment you all can do at home right now. I’ve used this example as well before, but this is very specific in terms of this rotation, and to speak about the balancing correction of the hand applying torque to the pivot point of the inverted lever? Yeah.
Stand on one leg, extend both arms out to the side, basically mimicking a one arm handstand in straddle, on one leg. Then you close your eyes and as you close your eyes, you feel your foot blade moving faster to correct your balance. Your legs wobble more and so on. This is fine.
Now you’re going to take your arms and hold them overhead. You grab your hand so they’re together above your head. Then you do the same thing, stand on one leg and close your eyes. Notice how much faster the blade of your foot will have to work. It will be very direct analogy to the one arm handstand. On the foot, since you’re so acclimatized to balancing on it, you will just immediately feel this quicker oscillation of the foot happening, with the legs together over your head. You will also feel the rotation quicken. Your shoulders might jerk out to the side quickly and you have to reestablish very fast. This is an apt comparison of those two in relation to these physics.
HF: Just to tell people a bit about physics though, the concept of angular momentum and conservation is all around us, basically. It’s like the Force.
The reason why the solar system rotates is because the thing that formed the solar system rotated. Before the solar system was the solar system, it was a cloud of dust. Before that cloud of dust, there was a sun or star that exploded into a supernova.
That sun or star rotated, in the same direction we rotate, and the earth rotates. The earth rotates around the sun. The rotation of the earth is like the conservation of the rotation of the thing it actually came from.
It’s used a lot in physics. When we describe systems it allows us to simplify things. It’s the same in handstands. For us it’s just simplifying calculations.
There was one thing I was thinking about. Okay, people always ask, what do you do? You’re in a straddle and start rotating. What should I do?
And what did you tell me a million times, Mikael?
MK: Just don’t allow yourself to fucking rotate. I would assume in my very limited physics understanding that somehow through this understanding of this code of the one arm handstand, you need to find a way to apply the opposite force somehow to this rotation, to be able to stop it.
HF: The idea is obviously you shouldn’t rotate. Then we think, where would the rotation be coming from? Most people will not rotate their spine, so it’s probably coming from the shoulders. So, locking the shoulders in place. That’s why recently I really like the idea of externally rotating the shoulders, or at least thinking about it a tiny bit.
One thing I’ve seen, since there are people around me here in Iceland starting the one arm journey, and I see a lot of bent legs when they start rotating. It’s very classic. People start rotating, and especially if the top leg is going over they will bend the top knee of the leg.
Why? Because they shorten the lever. They’re going to rotate faster by doing it. The initial rotation is now bringing their centre of mass outside of base of support, so they are losing the balance. Oh my god, it’s actually going out, I’m going to bend my knee to try to move it back in. This makes them rotate faster and even spinner out faster.
But you can obviously save it that way if falling, but it’s interesting because you see people doing it all the time. They don’t realize it’s rotation, they think it’s a linear fall out.
MK: I thought about that quite a lot. If we assume the pressure from hand to hip is rather stable and solid, and you begin falling into over balance on one arm, I would assume that within the statistical probability of you falling directly over, meaning both outer points of your legs will start moving backwards at the exact same speed and time – it’s a possibility, but extremely unlikely.
What tends to happen then, is as that over balance happens, it starts to manifest to us viewers and performers of the skill as some sort of rotation. There is so little probability of it not starting to rotate as it falls in that direction.
If we’re thinking about the torque from the hand, and ability to move the shoulder and so on-
EL: This gets into the level of levers, and deformable levers. You’re always making the assumption in physics the lever can’t deform, but the human body can deform under force. Force also transmits as a wave. I apply force at my fingers, and that takes a while to propagate to my centre of mass and correction, or provide something to do the correction against.
MK: Is there a way to calculate the speed of that? A random question out of my ass. If I apply pressure to the floor with my fingers, how long does that actually take for it to act upon my centre of mass? Suffer !
EL: I actually looked into this, and you can….you can work it out with a high speed camera and pressure plates. They have done it for running. Then it gets into tendon stiffness and how fast tendons will store and transmit force across them.
HF: If it’s just a stick it’s pretty much instantaneous. But we’re not sticks, so that’s a problem.
MK: There’s also muscles that need to tense up the chain specifically.
EL: We got from fluid filled, organ and bone sacks to sticks. Now we’re back again, tell us more about your fluid dynamics and how they work in simple harmonic motion.
HF: You could do this. The paper you sent me, Emmet with calculations for the human body – that was an old…you could do simulations of this stuff, which would basically be the only way to do it. You could simulate it, write a program that calculates all this for you.
It’s technically quite simple.
EL: I think the correct thing is you could write the program for us. I don’t think my programming skills are good anymore.
HF: I’ll wait until my kids are in high school, and have them solve the problem.
EL: I think we’ve given a lot of people some stuff to think about. I think we’re going to end it on that point.
I’m going to shout it out for anyone who’s managed to make it this far in the podcast. Hopefully you got your notebooks out and are doing equations and want to send them to us.
If you have any physics questions or anything else, send them to us @HandstandFactory or via the contact form on the website. We’ll see if we can get Helgi to answer them for us, or we can answer them ourselves with our made up science.
MK: I’m sure this could also be a topic to come up again in the future. Once we flesh out the thinking around it there’s more to dive into.
EL: I was trying to work out the three dimensional vector forces into a one arm handstand, and how we can translate the moment of inertia to the raising of the centre of mass to the rotation speed, and basically give every handstand a battle rating. How hard is this handstand? You’d know.
It was giving me some interesting stuff, so that’s something to look forward to.
MK: Thank you to Helgi Freyr, the ultimate life form.
EL: Helgi, if anyone wants to check you out or find out more about you, where can they do that?
HF: Mainly on Instagram, @Helgi_Freyr. That’s about it. I run a gym called Primal Iceland. We sometimes host these two guys, Emmet and Mikael. They’ve both been there quite a few times.
EL: They have an awesome sauna and…cold things.
Iceland is amazing and if you want to go for holiday and do some handstands, check out the gym Primal Iceland. Definitely gets three thumbs up. The funny thing is they’re above one of the biggest Crossfits, but we never stepped into the Crossfit because Helgi’s gym is so good. Not saying the other is bad, Helgi’s is just better.
We’re going to wrap up now. We’ve been Handstand Factory, that’s been Helgi. Thank you so much for listening, see you next week.