Lesson video

Hello and welcome to today's lesson.

My name is Mrs. Brooks and I'm gonna be taking you through the topic of muscle contraction, specifically looking at the different types of muscle contraction.

And this works really well within the unit of the specification, the musculoskeletal unit, and also when you're doing some analysis of sporting movement.

By the end of today's lesson, I hope we will be confident in explaining the different types of muscle contraction and also linking them to a variety of sporting examples.

Our key words for today's lesson are actually the types of muscle contraction we are going to unpick and learn more about.

The first one is isotonic, and we will learn that this is muscle contraction where we get limb movement.

In contrast, muscle contraction, that is called isometric, there isn't any limb movement, and actually the length of the muscle doesn't change, and the movement often stays still because the contraction is constant.

We will go into a bit more detail and learn specifically about two types of isotonic muscle contraction, one of which is concentric, which is when the muscle length gets shorter, and eccentric is when the muscle contracts but the muscle actually lengthens.

So welcome to the lesson.

We're going to start by looking specifically at the difference between isometric and isotonic muscle contraction.

And Lucas is gonna get us started by saying he was in the gym last night and actually overheard a personal trainer talking about muscles and the fact that they can contract in different ways.

And then he wants to know if that's true.

I understand why he would overhear that 'cause it's very common for trainers to set exercises that are either working on isometric muscle contraction, which is when there's no change in muscle length.

So that exercise will probably involve the client holding a position or a movement, but their muscles will be tense.

Or the trainer can be looking at exercises where there's isotonic muscle contraction.

So by that it means that the muscle does either change length and that therefore causes movement.

So actually the answer to Lucas is yes, this is true.

So if we wanna look at this in a bit more detail, we could probably use the press up as an example.

Don't worry, I'm not gonna ask you to do them.

However, you might find that you want to, to get a real sense of what I'm sharing with you.

So for example, if you were in this position here, which is at the top of a press up, and you might just be holding it before you start, the keyword there is hold.

So that position, your muscles will be tense, but the muscle length in the arms is not changing 'cause there's no movement.

So we refer to this as an isometric muscle contraction.

Now if I then asked you to lower to the floor, like what's happening in this image, because your muscles particularly in your arms are contracting and changing length, we refer to this as an isotonic muscle contraction.

So we have to go careful 'cause they're both iso.

No change in length is metric.

Change in length is tonic.

So we've got a footballer here in this image, and if we look at the sport of football as an example, most of the time our muscles are working and creating movement.

So in that game of football we're able to run, we're able to kick, we're able to throw, we're able to maybe head the ball, right, but our muscles are always working so that our limbs can move to allow those sporting actions to take place.

However, there are some times where isometric muscle contraction may happen and that is where there's no visible movement.

So we probably can't think of really key examples in football, but we might do in other actions or other sports where the muscle is really tense but there's no change in length.

So now we've looked at those two types.

Let's just do a quick checkpoint.

Is this true or false? Isometric muscle contraction is when the length of muscle changes under tension.

I'll give you five seconds to decide.

Well done.

That is in fact false.

And that is because what we see in there is a description of isotonic muscle contraction.

Isometric is when that muscle length does not change.

Okay, so can you think of some examples of isometric muscle contractions? So where the body's in a static position and the muscles will be tense but there won't really be any movement, they won't be changing length.

Maybe you can discuss that with the person next to you.

Now Aisha, when she had this conversation, she actually went to a sprint race and said that, you know, at that point where you're asked to hold, you know when they're kind of in the blocks and they come up on the "get ready" and the "set," and they have to hold that position before the gun goes off to to form that sprint start.

If they go any earlier, they might go too quickly and they have a false start.

But Aisha's right, at that point, those muscles will be really tense but they'll be holding that position to be really still to then get that really fast start.

Jacob kind of went to circuit training and was thinking about some of the things he might do in those circuit training activities and chose the wall sit.

And that is often an exercise that individuals are asked to do where they go and put their back against the wall and they sit in a position, a little bit like a squat position but they're back against the wall.

And they stay there and their muscles are really, really tense but they're not changing length.

So in essence, the muscles are being worked in a slightly different way than if they were gonna be changing length.

So in this instance, Aisha and Jacob have come up with some really good examples of isometric muscle contraction.

Here's another really good example from a gymnast, and you've only got to look at that image and know that, one, that gymnast is very still, but look at those muscles, particularly in his shoulders.

Look how you can visibly see the tension.

But they are very still, they're not moving.

All right, so that iron cross, as we refer to it, is another example of that isometric, that static muscle contraction.

So we've got three images here.

Which out of those three images do you also think is an example of isometric muscle contraction? Just give you a couple of seconds to decide.

Absolutely, I agree.

Option A is our example there of an isometric muscle contraction.

We can see the gymnast, a little bit like our previous gymnast, is in a handstand position on the beam, and no doubt she's having to hold that because that will get her some really good marks for her beam routine.

Whereas our swimmer in the middle, that arm is going to continue to move so the muscles will be contracting and causing movement.

And likewise for our basketball player, okay, bouncing the ball, there will be that movement in that upper and lower arm.

We've got a slightly different sport here.

This is really useful for us to keep thinking about lots of different, like a breadth of sports.

So we can see this tennis player is just about to serve the ball.

And that's a good one to look at, 'cause sometimes there might be a really short amount of time where the athlete might hold an isometric contraction before then going into an isotonic.

So we can see her, as she's holding that position, it's a really brief moment, but her muscles will be tense and not changing length, but that then allows her to then swing through and hit the ball.

So she'll get that isotonic contraction of her triceps to extend the arm, extend the elbow and hit the ball.

And some people refer to this as like a back scratcher position.

A good way of trying to learn how to then use the first phase of the tennis serve.

So that small hold is where we use isometric before then going into isotonic muscle contraction.

So let's look at another checkpoint.

Now we've looked at a few examples.

There are some even more here.

Which of these is an example of isotonic muscle contraction? Absolutely, it's our athlete that's running, she's doing her run up before executing or throwing the javelin as far as you can.

We know that because the sumo wrestlers in option A and the dancer in option B are both in a position of static contraction.

So they are pushing or holding, so their muscles will be tense but won't be changing length.

Whereas for our javelin athlete, there'll be lots of isotonic muscle contraction in the legs to allow her to get a nice fast run up before releasing the javelin.

So let's allow that to consolidate and go on to our first task.

We have been given two questions here, quite common questions on this topic area where you are asked to define, to show your knowledge of the muscle contraction, and then apply that knowledge by giving a sporting example.

And just a point to raise here that make sure the sporting example is specific, i.

e.

there is no ambiguity or it couldn't be vague and it couldn't be clear which muscle contraction you're actually referencing.

Pause the recording and come back to me when you're ready.

Okay, so for our first question, the one on isometric you could have written something like, "Is when the length of the muscle does not alter," particularly when there's that state of tension.

So that's the knowledge.

And what I like about this sporting example is it doesn't just say handstand, hoping that someone who's marking it just knows what you mean.

They're being really specific by saying holding a handstand.

So being in that position where you have to stay for a period of time, that could have been our wall sit, our iron cross, our sprint start or holding the sprint start before going.

For isotonic, hopefully you wrote the opposite of that and reminded us that is when we do have that limb movement.

And there are multiple examples we could have spoke about there, some of which we spoke about in this first part of the lesson.

Just look at how this then does reference the muscles and the fact that they might be extending the knee to kick a ball.

All right, so they're almost referencing that change in length to be able to extend the knee and then link it specifically to a sport, so that could be a football or a rugby ball.

So now we feel confident between the difference between isometric and isotonic, we're gonna dig even further and look specifically at isotonic muscle contractions and how they're divided into two categories.

So one of which is known as concentric muscle contraction and the opposite of that is eccentric muscle contraction.

And we can see in the image there that the athlete or the individual is using a weight, and if you've got one to hand or something that you can just simply what I would say curl up and down, so move up and down, you might be able to do the movement at the same time to really get a feel about what those muscles are doing.

So if we look at concentric muscle contraction first, that's when the muscle length is shortening.

Now look at that image there, look what's happening on the upward phase.

We can see that bicep muscle, that muscle that is located on the front of the upper arm, as that weight is coming upwards, that muscle is actually shortening.

Just take a look at the arrows, they're actually coming towards each other, the arrow heads which is trying to represent that that is a shortening of the muscle.

So a really good sporting example of that would be the upward phase of a bicep curl.

So we couldn't just write bicep curl, we'd probably wanna be really specific by saying the upward phase.

Now we can probably see on the way down as that weight is being lowered, the arrow heads are changing and now they're going outwards.

So that is showing that we've got an eccentric muscle contraction and that's when the muscle length is, sorry, the muscle is lengthening whilst contracting.

It still needs to contract because it's got to lower the weight.

Now, often that does happen to kind of counter, cause a counter effect in terms of what gravity is doing.

Right, so often, gravity will pull objects down towards earth, and an eccentric muscle contraction sometimes is trying to resist that or prevent that.

In this particular instance though, an example is that downward phase of the bicep curl, shown really well there in our little moving arm.

So to ensure we feel confident in terms of the eccentric muscle contraction, which of these options in our checkpoint is correct for the definition of eccentric muscle contraction? I'll give you five seconds to decide.

Really well done if you went for option C, that's the eccentric muscle contraction when there is lengthening of the muscle.

Not shortening, which is concentric.

And remember from our previous learning, isometric muscle contraction is where there is no change in length.

Okay, let's now try and in the same way we did in the first part link these to sporting examples.

So look at our individual on the screen there, he's doing a squat.

Can you guys do a squat? Can you go into that starting position, shove the hips back and lower yourself down, and come back up to standing? Just like he's doing.

As you're doing that, what muscles do you feel are working at the knee joint? What are the ones that are really quite tense in that movement? And I'm hoping you are all saying the quadriceps, that group of muscles, big group of muscles at the front of the thigh.

And that we refer to them as the agonist, all right, the muscle that are doing the work, the muscle that's causing that movement at the knee joint.

And if we need to just break it down, we've got that starting position, then we go into that downward face, we get that flexion of the of the knee joint, okay, the knees bending, we can see the angle has got less.

And then as you come back up, we reference that as the upward phase, which is when the knee joint extends to allow you to come back to that standing position.

Now, Alex is quite rightly saying, okay, I understand the squat, I've had a go at it.

Which of that is a concentric muscle contraction? When is it eccentric? And that's a really good question for Alex to ask 'cause the squat is a really common example to reference concentric or eccentric muscle contraction.

So let's break those movements down and let's think specifically about the downward phase, so we can see which one of those that is from the image.

Now remember what I said about gravity.

So gravity pulls us down towards earth.

So when we're going down in the downward phase of the squat, we almost need to control the movement and resists that gravity.

So in this instance, the quadriceps are flexing the knee but they are lengthening, okay? So they're getting longer as we go through that movement.

So therefore that is the example of eccentric muscle contraction.

And you might need to stand up and do it again and almost feel like you can sense that happening in that upper thigh.

So as you go down into that movement, your quads are doing this like an elastic band, which means if you think on the elastic band, if we pull something that way, if we let go, it's just gonna come back to where it was.

So almost happens in the squat.

So on that upward phase, the quadriceps have to shorten, they have to return back to that upward position in order to extend the knee.

So because we know concentric muscle contraction is shortening, the upward phase of the squat is an example of concentric muscle contraction.

Okay, so with concentric in our mind, which of these three actions is correct for concentric muscle contraction? I'll give you a few seconds to decide.

Well done.

C is showing the bicep curl, okay? So bringing that weight up towards the shoulder, towards the chest and that then would mean like our little arm video showed that is a concentric muscle contraction.

Whereas the individual in option A is holding that plank position, so her muscles aren't changing length, and actually the individual is in a similar position in B in that they're holding the squat or they've gone to the downward phase of it, which we've now identified is eccentric muscle contraction.

So that takes us onto our second task of this lesson where we are being given a set shot in basketball and we can see the image there.

Now, this task kind of gives us some different variety in how questions can be asked on this topic area.

So you can see for question one the muscles are already being stated, the triceps, but we are being asked to describe how they contract during that set shot.

Whereas question two is given as the joint but not the muscle, but still wants us to describe the muscle contraction occurring in that movement.

So that's question one and two.

And question three is also quite different but still asking questions on muscle contraction.

The movement shown is a press up and they're being asked to identify the muscle contraction in the downward phase.

All right, so the question will always specify which phase of movement they want you to look at.

And then they want you to build on your answer once you've identified that and actually say why.

So when we have to justify something, we have to support a case with evidence.

So if we've said something, we need to back it up with why we think that.

So pause the recording and have a go at question one, two and three.

Welcome back.

So for question one, how did you do? We knew it was the triceps already.

Hopefully you then said that they will shorten.

Okay, so as we go into this movement, you can almost feel it for yourself.

If you go from there to there, you can see that the muscles have got shorter, they've almost gone bulkier, all right, so they've shortened in length.

And for a set shot specifically, that's so that you can extend the arm to reach up towards the basket.

So that is an example of concentric muscle contraction.

So is the one at the ankle joint, although remember we weren't given the muscle in the question.

So this answer quite rightly picks up on the fact that that's the gastrocnemius, that muscle in the back of the lower leg, and the fact that that's also going to shorten to allow that individual to go up onto their toes and then push and help them push that basketball towards the basket.

Whereas for our press up, we would've identified quite the opposite 'cause this is the downward phase.

So remember we've got that resistance of gravity.

So this is actually an eccentric muscle contraction on the way down.

And then to justify that to support that case with evidence, we would use our understanding of eccentric muscle contraction, knowing that our triceps are lengthening to control the movement towards the floor working against gravity.

If they didn't do that during a press up, then everyone would probably just hit their face on the floor, which is not what the press up is wanting people to do.

So now we know the difference between the two, and we've looked specifically at eccentric and concentric muscle contractions, our last part of our learning is where we now use this knowledge and do more analysis on sporting movements or sporting actions.

And I think we are probably all in agreeance that that's quite straightforward for isometric muscle contractions 'cause the action is being held, but then there's loads and loads of actions in sport where we get that isotonic, that moving contraction.

And I think we recognise that sometimes that can be hard to differentiate whether that is a concentric muscle contraction, i.

e.

getting shorter, or it's eccentric, which means it's getting longer.

So, we're gonna have a little bit of an opportunity now to practise this, so we feel that we can identify correctly concentric or eccentric.

So let me introduce you to a tricep dips or dip, sorry, triceps dip exercise.

It might be that you're in a position where you are that you can have a little go at this.

So you might need a bench or a chair or a table even.

And you need to get yourself in that first position, which I'm going to reference as position A.

And then you're going to try and lower yourself to the ground.

Don't have to touch the ground but just lower yourself.

And you see the elbows are almost at 90 degrees and that's you going down dipping to that position B, hence why it's called a dip.

And it's a really good exercise to emphasise the triceps.

Now if we look specifically at B, let me take you back to what we learned about the squat and the press-up, all right? This is the body is having to lower themselves to the floor, which means that the triceps will be contracting eccentrically.

All right, so you get that flexion of the elbow but the triceps are actually lengthening to cause that flexion whilst controlling the movement and working against gravity.

So the key word there is that muscle will lengthen.

So I've just have a quick checkpoint at this stage.

We're being asked here if this is true or false.

A wall sit exercise is an example of eccentric muscle contraction.

So we've looked at the tricep dips.

Is it true or false that the wall set is also eccentric? And if you ticked false, that's correct.

Why is that the case? Well, we know in the wall sit, they're gonna be in a state of tension but they're not gonna be changing length, so that's an example of isometric muscle contraction.

Another exercise we could look at though is a sit up.

So we can see here that we've got position A where they're in that almost starting position, and then the body or the upper part of the body specifically curls upwards.

You can see that the hands are almost reaching towards the toes, and the head and the shoulders have actually come off the floor.

All right, so those abdominal muscles, those big muscles in the front of our upper body often referred to as our core muscles are doing quite a lot of the work here.

Now when they're moving from that A to B, they're actually gonna contract but they're also gonna get shorter, so we know that this is a concentric muscle contraction.

And that shortening is just to allow you to get your head and shoulders off the floor and perform that exercise.

So if we revisit our biceps curl, this our second checkpoint, which muscle contraction is used in the upward phase? Trying to really reinforce the referencing whether it's an upward or a downward phase.

What would your answer be to this question? Well done.

Okay, that's a concentric muscle contraction.

So as we saw in our little image, that's that moving, getting shorter as it comes up towards the chest.

Okay, final practise is really developing our ability to analyse movement, and where relevant, justify our answer.

So in our first question, we are being given a footballer.

The position A to B are being used in the same way we've been using them throughout the lesson, and they've specified the joint.

So they want us to know what the muscle contraction is at that knee joint when the position is moving from A to B.

So often, we've gotta work out which muscle is the agonist, the one that's doing the work, and then consider what the muscle contraction is.

And once we've done that, we support a case with evidence.

We just say why we think that, and our knowledge of the muscle contraction will help us do exactly that.

After you've done question one, we've got a similar question, only the exercise now is a calf raise, and we're being asked to look specifically at the ankle joint.

Notice in this one that the position A, the athlete is already on their toes, they're in that raised position and B is when they're lowering their heels to the floor.

And finally with question three, we're being given a plank exercise or plank position and asked to identify the muscle contraction for this particular action, and again, support our case with evidence, justify our answer.

Pause the recording, take your time on question one, two and three, and then come back to me when you're ready.

Okay, how did we all do? So we first of all had our football kick.

You could have written something like this, just notifying that it's the concentric muscle contraction, and you will have worked out that it's the quadriceps that are extending the knee.

So your justification is the quadriceps will shorten as part of their contraction in order for the knee to extend, so that they can kick the ball.

For the calf raise, it was the opposite, 'cause remember they were coming from their toes actually lower into their heels.

So at this point, the muscle contraction is actually lengthening to allow the heels to touch the ground.

It's really great practise to mention the muscle that's been used, which is that gastrocnemius.

And you can see that this has been written by even using the correct movement terminology, which is dorsiflexion, okay? Which is when you are not pointing, but when you are lowering your ankle towards the floor.

And finally question three, that was our plank.

Hopefully you all recognise that that was our example of isometric muscle contraction, 'cause when people are holding that position, their muscles will be tense, so the justification is there is tension but there's no change in length, so the position can be held or that the individual can remain still.

So well done for identifying those three, but more so being able to just add a sentence and use your knowledge to justify why you've chosen that muscle contraction.

Now to finish with this task, we've given lots of variety there of different movements, but sometimes you might be asked to actually pick a sport and then give an example of each of those three types.

So to finish with that is your last part of the task.

Can you pick a sport and then think about three different movement examples that would be really good examples for either isometric, eccentric, and concentric muscle contraction? Pause again and then come back to me when you're ready.

Now I'm aware that there could be lots of different answers here 'cause it all really depend on the sport that you have chosen.

And I hope as you maybe discuss this with each other, you are able to give a real, give some real breadth of ideas in terms of the sports that you have chosen.

But on the screen there, I've just given one example from rugby, and for the isometric, I spoke about pushing in the scrum 'cause it's really common that 'cause you're pushing against each other, there may be times when your muscles are so tense but they're not moving 'cause you're almost trying to push against an immovable force.

Eccentric, I reminded myself of that squat is a really good example.

And then I linked that to, you know, the scrum half, that player that goes into the back of the scrum, always gets in that really low position to pick the ball up, and then be able to pass it onto the backs.

At that point when they're squatting down, as we've learned from this lesson, the quadriceps specifically working at the knee joint will be in that eccentric muscle contraction, 'cause that scrum half player stays really low to stay in that position before they stand to execute the pass.

And then for concentric, I remembered us talking about kicking a football and then I then linked that to, or transferred that to a similar skill in rugby and knew, you know, often there's that one player that will kick the conversion after there's been a try.

And that follow through, once they kick the ball towards the post is when you get the extension of the knee, and therefore that's a really good example of concentric muscle contraction.

Hopefully that will help you just check against yours to see if, one, you got the three muscle contractions covered, but also you were really specific in your answers, so you made it really clear about those skills, those movements from the sport that you have chosen.

Okay, let's summarise what we've learned today with regards to muscle contraction.

We know now that isometric muscle contractions do occur and when they do, we won't see a change in muscle length and there'll be no movement.

The opposite of that is isotonic muscle contractions and they do result in limb movement.

And we have two types.

We have the concentric muscle contraction and that's when the muscle shortens.

And then we also have that eccentric muscle contraction and that's when the muscle lengthens.

Hopefully that has really helped in terms of muscle contraction.

Thank you for joining me today and I look forward to seeing you on the next one.