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Physical activity and the body

Michael Trenell talks us through one of these tests, explaining what is happening to heart rate and breathing, and what this means for our health.
Fitness is really important to ageing well. And fitness, remember, is not about running around a running track. It’s about your ability of your body to do different things. It’s how well your heart works, your lungs work and your muscles work. We measure this doing a maximal exercise test. Now this is where you pedal up an impossible hill or walk up an impossible hill, where it get steeper and steeper. And we can look at how well your heart, lungs and muscles work at all points through that. What we’re really interested in is the maximal amount of blood that your heart can pump, air that can go into your lungs, but also the maximum amount of oxygen that your muscles can use.
The reason why we’re particularly interested in it with ageing is because as you age, your level of fitness decreases from about your mid-30s. And in later life, it’s a key determinant of your ability to do the things that make you you, so go to the shops, play bingo, see your friends. But also, it’s very important in terms of your risk for developing diseases, like type 2 diabetes, cancer and dementia. So it’s a really powerful biomarker.
The aim of this test is to look at the level of cardiorespiratory fitness. And the way that we do that is we measure it by getting people to cycle on a bike, and then they go up the impossible hill. So this is a hill that gets steeper, and steeper, and steeper, and it’s impossible because you never reach the top. But what it does allow us to do is measure how well the heart, the lungs and the muscles are functioning. And at the end of this, we’ll be able to see how much fuel they burn.
We’ve got all the data coming through well. We’re also measuring the ECG. Now, what this allows us to do is look at how well the heart is beating. And we do this because every muscle contraction is started with an electrical impulse. By measuring the ECG, we can just make sure that there’s nothing wrong.
How you feeling, OK? Good.
So if you’re OK, we’ll start the test.
So we’ve started the test now, and the amount of work that Dave’s having to do is going to get harder, and harder, and harder, and it will go up every minute. And the idea is for Dave to keep going as long as he can do, and it can show us the maximum capacity of the heart, the lungs and the muscle. We’re getting two data streams coming through. The first one is from this mask that Dave’s wearing. Every breath is taking a sample of the air that Dave breathes out. And it can measure the amount of oxygen and carbon dioxide from that gas.
And we use that to calculate how much oxygen is being used by the muscles and how much carbon dioxide, which is the waste product, is being produced by the muscles.
So as Dave is starting to exercise, one of the ways that his heart responds is by increasing his heart rate, which is getting more blood to go around the body. The other way that the vascular system responds is by increasing the blood pressure. So that’s where the blood vessels get a little bit tighter, and that allows the blood to go through and get to where it needs to go to, which is in the muscles not in the other parts of his body. Also the data coming through, we can see that heart rate is about 93, so Dave’s finding this really quite easy.
We can also look at the amount of oxygen to carbon dioxide, and this tells us how much fat is being burned. So the lower it is, the better. And at the moment, we can see this ratio is under one, which means that actually this is really easy exercise and that there’s lots of fat being burned, not lots of carbohydrates.
So you can see the heart rate is starting to go up now. It’s gone up from 90 to about 95. The work rate’s getting a little bit harder, but because we can see here this is still under one, so this is still really easy.
So the maximum that we’d be expecting for someone like Dave, who is relatively young, is probably 170, 180. Whereas for an older person, it’s less because the heart is relatively a little bit smaller. So here you can see the 12 channels from the ECG, which is showing us how well the heart’s contracting. We’re able to put those together to get a 3D map of how well each heart contraction is working. We can also see not only how the heart’s contracting, but also how it’s relaxing because you consume quite a lot of energy when your muscles relax.
And that’s quite important because if you don’t have the capability to relax muscle and it stays contracted, that’s not very good for the heart. Imagine it constantly being contracted. It’s also important for skeletal muscle in exactly the same way that you need the energy to help the muscle relax. It sounds crazy, but you do use a lot of energy just turning the system back at off again. So we’re starting to see the heart rate climb up as Dave’s having to work harder. And his heart’s working harder to try and get the fuel to the muscle but also get the waste products from the muscle back out again.
We can see that the muscles are working harder because the respiratory exchange ratio is getting higher. That means that Dave is taking in lots of oxygen but is also producing lots of carbon dioxide as his body is losing its efficiency slightly. Now, for somebody who’s relatively fit, like Dave, that threshold, where you go from being very comfortable to being slightly uncomfortable, or where you go from burning mainly fat to mainly carbohydrates, is about 70% of his peak. But for people who aren’t physically active, that could be as soon as you start exercising. And that’s why a lot of people who aren’t physically active find physical activity hard.
The heart rate is rising. Oxygen consumption is very good. Now, for somebody who is relatively fit we would expect a fitness level of about 40 or plus. An elite athlete has a peak aerobic capacity of about 70 or 80 millilitres per kilogram per minute. Normal people, people like me, are around about 40 to 50 millilitres per kilogram per minute. Somebody who’s old and somebody who’s inactive might have a peak aerobic capacity of around 20 to 25. That means that as soon as they start moving, they’re nearly working at their maximum. Five, four, three, two, one - and I’ll just put you into recovery.
So one of the things that happens after quite intense exercise is that when your body becomes less efficient, it produces a thing called lactic acid. Now, this is why most of us feel slightly tired when the muscles work. At the end of exercise, you should carry on going for a little bit. Now, this is not about cooling down, as in getting cooler. It’s about having the blood go through the muscles to try and clear out some of that lactic acid. It will help your muscles recover.
Great. We can see the heart rate recovering nicely. Heart is still beating very, very nicely and is slowing down as well. And it slows down as less oxygen is needed by the muscles.
Well done. Great.

Cardiorespiratory fitness is a useful way to assess physical fitness and can be objectively measured using an exercise stress test or maximal oxygen uptake test (VO2max). In this video, Michael talks us through one of these tests (taken here by our volunteer, Dave) explaining what is happening to heart rate and breathing, and what this means for our health.

Cardiorespiratory fitness is the ability of the circulatory, respiratory, and muscular systems to supply oxygen during sustained physical activity. Low cardiorespiratory fitness not only presents challenges for physical independence and quality of life but has been consistently linked to diseases such as type 2 diabetes, cancer and dementia.

Ageing is associated with a decline in cardiorespiratory fitness with VO2max declining at a rate of 1% per year after the age of thirty.

Is cardiorespiratory fitness something that you are aware of? Have you noticed any decline in your own fitness or in the fitness of friends/relatives?
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The Musculoskeletal System: The Science of Staying Active into Old Age

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