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What happens to our muscles when we exercise?

Michael guides us through a muscle function test and explains the different types of muscle contractions that happen during physical activity.
Muscles are integral to the way that our body works, whether that’s breathing, your heart, whether it’s about the ability to move around. And in ageing, they’re particularly relevant because muscles change with age. In particular, you start to lose muscle mass and muscle strength with age, and you lose about 0.5% to 1.5% per year. So we’re going to have a look at how you measure muscle strength, but also how you have a look at it in its different context, so when it is getting shorter, getting longer, and when it’s stationary. These are the three types of muscle contraction. But we’re also not just going to have a look at the bulk of muscle, but have a look at the neural supply.
This is the electrical impulse that makes the muscle work. The reason why it’s relevant for ageing also, is because as you start to move more, you keep the muscle function. As you move less, you lose muscle function. And this is vital when you’re old because if you don’t move, you lose muscle function. But eventually, you lose the ability to gain muscle mass back. So if you’re going to hospital, for example, and you don’t do anything, you lose muscle mass, your likelihood or your ability to regain it by doing rehabilitation when you leave is a lot less. We’re really interested in how muscles work, and there are three main ways that muscles contract.
The first one is called isometric, which means it contracts, but doesn’t really go anywhere. It’s like pushing against something. The second way is called concentric, which is the one that we’re most used to, which is where a muscle gets shorter. And the third type of muscle contraction is called eccentric, which is where you push against something, but the muscle gets longer at the same time. When a muscle contracts, there are two main things that are driving it. There’s the contractile machinery, so this is the actin and myosin filaments that work together and pull together to get closer. But the second part is actually the neural firing of that, and the two work together to create a muscle contraction.
In the exercise test, we saw the ECG, and the ECG was measuring heart contraction. Now this time, we’re going to look at an EMG which is where we can measure the muscle contraction of a different type of muscle. In this case, it’s the thigh. So what I’d like you to do now is push your leg out, which is a concentric muscle contraction. With this, the muscles on the front of Nduka’s thighs are going to get shorter, and what we’ll be able to see here is the torque, or the amount of contractile force, that the muscle can generate. We’re going to do this four times. The first two times quite easily, and the last two times a lot stronger.
Now at the same time, you’ll be able to see the electrical impulses coming through. This is the thing that makes the muscle contract. So four times, twice quite low, and twice a bit harder. OK? Off we go. You can see this is nice and easy, not much of a trace. And now give it everything. Good work. And again, great. And then just wait there. There’s quite an amount of energy being created by the muscle when it contracts. But it has a peak. It doesn’t start and it’s not the same all the way through. It’s at its peak after a certain angle, which is about here, and then it lessens down again.
Now, the electrical impulses are really important because you need them to make the muscle contract, but also, it needs to relax to go back to its original point. And this is something that’s very important in ageing because the ability to make a muscle contract, and also relax, is what makes the muscle function. We’re going to look at the second type of muscle contraction, which is called eccentric. Now at this point, the muscle is going to try to contract as hard as it can, but instead of getting shorter, it’s going to get longer. Now this is a pretty powerful machine, so no matter how strong Nduka is, it’s going to push him back.
So instead of just seeing the power on the way up, we’re going see the power on the way down. That’s important for exercises like walking down the stairs. So it’s where you’re trying to go down, and the muscle is getting longer as its working. Again, we should see the electrical impulse on the screen next to it. So I want you to do two, and I want to do them as hard as you can. OK, on your marks, get set, go. And push, push, push, push. Carry on pushing. Carry on pushing. OK, great.
There’s energy not only on the way up, but also when the muscle’s relaxing again too. Well done. Good test. The final type of muscle contraction is called isometric. This is where Nduka will push, but the muscle won’t get longer or shorter, just stay the same. So in a couple of seconds, we’re going to get Nduka to push his leg, but you won’t see it move, but you’ll see lots of energy generated on here. OK, now, push, push, push, push, push. Keep going. Nearly there. And relax. Great work. Well done.

Muscles are integral to the way our body moves.

In this video, Michael guides us through a muscle function test with our volunteer Nduka and explains the different types of muscle contractions that happen during physical activity;

  • isometric – stationary contraction in which the muscle contracts but the length doesn’t change
  • concentric – the muscle gets shorter
  • eccentric – the muscle gets longer

Ageing is associated with a significant decline in neuromuscular function and muscle mass. But whilst muscle deterioration is a natural process, a sedentary lifestyle can greatly accelerate it. As you move less, you lose muscle function, and as you age, you begin to lose the ability to regain muscle mass. Resistance training such as lifting weights, can help us to maintain muscle function.

Is resistance training something that you are aware of? Is this a type of exercise that you incorporate into your daily life?
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The Musculoskeletal System: The Science of Staying Active into Old Age

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