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Introduction to biomechanics

In this video, Kayla and Victor introduce some biomechanical topics and illustrate some important concepts for human movement analysis.
Hi. Welcome back. In this video, we’re going to talk about biomechanics. In the last video, we talked about anatomy, which is that study of structures of your body. Now, we’re going to apply mechanics to that biology and talk about how the body moves and what words we use to describe that. Do you have a favourite definition? For biomechanics? Yeah. Well it is a combination of biology and mechanics, I guess. Yeah, exactly. So it’s a pretty interdisciplinary field– you’ve got physics thrown in there, some biology, some medicine– so you’re going to use a lot of words that you may have seen in other classes.
What I like to do when I talk about biomechanics is to first break it down into two parts. OK, so the first is kinematics, and that’s what you can see– your angles, the positions. And then the next is the kinetics, what you can’t see, what’s going on underneath body movement– forces like good old gravity. So, Victor, do you have a favourite movement? Jumping. Jumping. All right, so Victor jumps, right? He jumped. So in the last video, we talked about words to use to describe what moved– anterior, posterior, flexion, extension. Now, we’re going to talk about how we actually analyse these. There’s different ways to describe Victor’s jump, itself. We could talk about how high he jumped.
We could also talk about how good his jump was. When we quantify things, those– or we could qualify things. So how would you rate yourself from a qualification of your jump? Mediocre. Yeah, all right. Do you know how high you jumped? 20 centimetres? OK, so those are just difference in quantitative variables and quantitative variables. Now if we’d talk about, say, kinematics– you saw that his foot position changed. We could say if he jumped 20 centimetres, his toe moved 20 centimetres. We could also talk about angles, because we have both vector and scalar options. Could you give me a difference between your jump, in vector and scalar?
Vector and scalar could be the speed of the jump– Yeah, so if he jumped, say, at 3 metres per second, that was a speed. If we then make it a vector, we say he jumped 3 metres per second in that upwards direction. So vectors have magnitude– or what we call a direction– to it. So in biomechanics, you’ll see a lot more vector quantities because we talk about how something got from one place to another, not just general scalar quantities. Another thing we like to do is talk about the difference between linear and angular. So when you watch Victor jump, you’ll see that his body moves linearly up.
But his knees, because they’re bending and rotating, they’re actually moving angularly in that knee joint. So they’re moving about the knee angle, in that rotation term. So those are other ways to describe our kinematics. You talked about metres per second, before. What’s the word for that? Speed. Speed. And then, we also have velocity. So if we go even further, to how fast your movement is changing, you have acceleration– how much your speed is changing. So right now, Victor is not really accelerating up at all. But then, all of a sudden, he accelerates up fast, stops, and comes back down.
So those are our three main things we talk about is that distance, the position, whether it’s in scalar and vector; that velocity, whether it’s in scalar or vector– as just a speed or velocity with a direction– in a linear and angular way; and then also acceleration, that change in rate of velocity. Those are our main kinematic variables. In kinetics, that’s a little harder to look at. So right now, Victor actually has a force applied to him. Do you remember what we talked about in the beginning? What’s my favourite force? Gravity. Gravity. So that gravity is keeping Victor from floating out into space. So the gravity is pushing up into Victor, and Victor is pushing back.
If he pushes down more, he’s then pushing against gravity to build up some energy in his body, and then release that kinetic energy so he can move upwards. So what actually happens internally, in his body, is he’s using his muscles to create kinetic energy to actually move that power into generating a jump.
Do you have a favourite force, or do you also like gravity? It was gravity. Gravity is pretty good, too. I like staying on the ground. So forces also exist– a big thing when we talk about kinetics is static and dynamic. So static is when you stay still. So that’s how we look at how his body is moving. So if we’re going to do a static analysis of his body, the force applied would be from gravity up, and then the weight from his body down– so that counterbalance to keep him stationary. When we talk about dynamic motion, it is how the forces then go throughout your body to create movement.
So, say, if I was going to push Victor, I’m then putting a force onto him that makes him go from static to dynamic movement. You can quantify that force, or you could just qualitatively say, Kayla, that’s mean. The other aspect, with kinetics, that we like to talk about is balance. You’ve done a bunch of work with balance, right? Yeah. Yeah, so balance is just that ability to stay at equilibrium. And so you could see, Victor is just balancing on his two feet, here. When we look at balance from a quantitative perspective, we actually look at that centre of gravity. Do you know where your centre of gravity is? Around here. Yeah, it’s just a little bit below your belly button.
So right now, because we look at– all of his body has different weight, his centre of gravity is right here. But if he was going to stand on one foot, his centre of gravity would shift because there’s only one point of contact with that force. And then if, say, you were going to move to the side– yeah, can you stay like that? I can try. Yeah, how’s your balance, there? So his centre of gravity is shifting even more. And then when he can’t overcome, internally, that centre of gravity, he loses his balance. I almost fell. All right. So that’s just a basic introduction to human biomechanics.
There’s a lot more in our worksheets, and then there’s a lot more if you want to go look at any other type of physics textbook or biomechanical resource. Remember, this is a little bit more complicated than you might have seen, but there are a general set of vocabulary that’s used to describe things. So as you’re talking about movement, there’s different things that you can analyse– that you might know existed– and then there’s also different ways to describe what you’re analysing so that everybody can understand. Again, it’s important to note– you don’t have to memorise this now. This is just an introduction so that you know these things exist, and then you can look for them.
When you read something and you find these terms, you know what they mean and you can come back to this video and review these things. All right, see you later. [EXIT MUSIC]

When we try to analyse human movement, we use concepts and tools from biomechanics.

In this video, Kayla and Victor introduce some biomechanical topics and illustrate some important concepts for human movement analysis.

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Motion Capture: The Art of Studying Human Activity

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