Cardio exercise: How much do you really need?
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Hello and welcome to Zoe Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolfe and today I'm joined by Professor Javier Gonzalez, a professor and world expert on nutrition and exercise. And today's subject is cardio exercise.

Now, most of us know that we need to exercise regularly to get health benefits, but it's often hard to work out exactly what sort of workout and how much of it we should be doing. We're often inundated with different methods and formats like HIIT training, endurance, circuit training and even Zumba.

And each one of these promises certain improvements to our health. So the whole thing can get quite confusing. And what we really want to know is which one of these is best? And is it better to stop one of them in favor of another? Well, that's the million dollar question. And luckily, there's some great research we can call upon to help us answer it. OK, then let's get moving. So, Javier, I was talking to a friend the other day who wants to do more exercise, something that I'm sure many of our listeners are familiar with.

My friend, she's a busy working mother and she's finding it really hard to figure out what would give her the best bang for her buck.

And as you said a minute ago, she was looking at all sorts of different types of exercise classes that she was discussing with me. HIIT classes, Zumba, yoga, you know, to name the three that I remember. And she was telling me that she's specifically interested in cardio exercise. Now, before we go any further, I hear this word cardio used a lot, but I'll be honest, I don't really understand exactly what it means. Can you explain it? Yes, I think we should perhaps firstly address what isn't considered cardio.

And that would be things like strength type activities, things like weightlifting. And these activities are sometimes called anaerobic activities. And that word means your body is generally creating movement without using oxygen.

Alright, so Javier, so far it's getting more complex, not yet. What does this mean to say not using oxygen? Because I know that when I'm weightlifting, I am still breathing and if I stop breathing, I'm in trouble fast. Yeah, so our muscles can produce force and movement using different energy pathways. Some of these pathways require oxygen and others don't. And when we're doing this strength exercise, we're mainly using the pathways that don't necessarily need oxygen.

But the downside to these pathways is that we can only use them for very short bursts of activity. Got it. And so I guess if strength isn't using oxygen, then cardio exercise is where I am using oxygen? Yes, that's right. Cardio exercise is generally called aerobic exercise.

Anything like jogging, hiking and most team sports have a big aerobic component to them. And these types of activities are utilising your cardiovascular and cardiorespiratory systems. These are the systems responsible for drawing oxygen into your lungs, through your blood and into your muscles.

Now, Javier, help me to understand this a bit more. When someone does an activity like weightlifting or strength training, the effects can be quite noticeable, right? Their muscles may be getting bigger, their body shape may be changing. But with cardio, would I be likely to see results like this? Is that what you're aiming for? Not really. You may get some of those same effects, but the main benefits of aerobic exercise are more internal.

And put simply, you're improving the capacity of your heart and your muscles to utilize oxygen. And the best way we measure this is something called VO2 max. Okay, so we're getting a little bit geeky, which I partly love, but also always want to make sure I understand. What is VO2 max?

And what does it tell you, Javier? And you're a professor, so what would it tell me? Yeah, so let me get a little bit technical for a second, but then I'll bring it back to the basics. It's going to be worth it. So VO2 max is the maximum amount of oxygen that an individual can use during intense or maximal exercise. So the higher your VO2 max, the better your cardiovascular and cardiorespiratory systems are functioning. Got it.

Got it. So I'm thinking a bit like in the olden days when you used to buy a car and they'd like tell you how fast you can go from zero to 60. It's sort of like this measure of your peak performance. And so you're saying it's sort of how much oxygen I can use during exercise. And so therefore, I guess, practically speaking, like how well my heart and lungs are working. Is that right, Javier? Exactly. Yeah. And so what is considered a good VO2 max?

So it varies depending on age, gender, and of course, the amount of physical activity that we do. And for someone like me, a good VO2 max might be somewhere between 44 and 51. And this number is the milliliters of oxygen that I would use per kilogram of my body weight in one minute. So looking at you, Javier, if you're 44 to 51, I'm guessing I'm probably 10. Yeah.

So how important is it to have a good VO2 max, or maybe if you can't measure that, like how important is it to have this good cardio fitness when someone is listening to this and they're probably thinking about their overall health, right? They would like to live more years of healthy life. Well, it's absolutely crucial, Jonathan. It actually turns out that the level of someone's cardiorespiratory fitness is a very strong indicator of

of how at risk they are of getting certain cardiovascular diseases and also overall mortality. So just to make sure I've got that, what you're saying is that someone's cardio fitness level can predict not just their risk of heart disease. And I think, listen to that, there's certain logic, like your heart is sort of a muscle and we sort of have that link. But you're also saying it's their risk of dying from anything. And then amazingly, this sort of cardio fitness level is actually...

more reliable thing than their weight, whether they smoke, even if they have type 2 diabetes, to predict whether someone is going to die. Yes, that's right. Compared to all of these, cardiorespiratory fitness is an often overlooked measure from a clinical perspective. So that's amazing. And part of why we're so pleased to have you here on the show. So I guess that means it's quite obvious that improving our cardio fitness is really important if we want to avoid those sort of

cardiovascular problems, you know, the heart and stroke and things like that, but just prolonging our lives in general. So I guess what I really want to know is how can we design our exercise routines to have the best chance of boosting the health of that cardio system and also being realistic, right? We all lead busy lives. There are lots of people like me who don't really love doing exercise. It's more something they do because they feel that it's

it's for their health. And if we go back to my friend who I was telling you about, right, she's really busy. She has young kids. So she's really interested actually in sort of how little exercise is going to be enough for her to get these health benefits. Yeah. So first of all, it's important to say that when it comes to cardio and exercise in general, anything is better than nothing and more is better than less. But if people have limited time to exercise and they want to try and get the very most out of the time that they have,

then there are three main things we can look at to optimize the health benefits of exercise. These are intensity, duration, and frequency. Okay, so we're getting a bit complicated again. So do our listeners need to use like a mathematical formula for these things to figure out like exactly how to work out? No.

No, they don't need a mathematical formula. Let me take you through some of the studies that have compared different types of exercise to help you understand how these factors work together. We can start with a review from 2015 in the journal Sports Medicine. They compared the health effects of people doing high intensity interval training to people doing more classical endurance or prolonged continuous training. And Javier, I keep asking these questions, what's the difference between those two types of exercise?

So high intensity interval training has become very popular recently. It involves short, quick bouts of high intensity exercise, one after the other, with short rest periods in between. So that might be one or two minutes of exercise and then another one or two minutes of rest in between those repeated bouts.

Whereas endurance training is of a lower intensity overall, but it's more prolonged. So a 30 minute continuous jog or continuous bike ride, for example. And this is sometimes thought of as the more traditional method of cardio. All right. So that's really interesting because the second one, they're clearly spending way more time exercising, right, than in the first with all the gaps. So it seems obvious that the one with longer time is going to be better. Right.

What did the researchers find out when they compared these two? Well, interestingly, both types of exercise elicited large improvements in the VO2max of healthy young to middle-aged adults. But actually, the gains in VO2max were greater with the high-intensity interval training compared with the more classical endurance training.

So just to make sure I got that, you're saying that the high intensity exercise, even though actually it had a lot more gaps in it, actually improved the participants' cardio fitness more than when they're just like literally nonstop for the full 30 minutes doing the endurance training? Yes, exactly. And we know that exercise intensity can act as a replacement for exercise duration. It's a bit of a trade-off. So if the intensity of the sessions is very high,

then less time is needed to obtain some of these health benefits.

So I think I'm finally starting to understand why my trainer likes me to do something that wipes me out in 30 seconds, which always feels really unpleasant. And it feels like we're getting a bit closer to the answer to our question. Yeah. So if we really want to know what the absolute minimum amount of time needed to get a benefit from exercise is, then one study has shown as little as six times 10 to 20 second sprints per week. So that's just six sprints per week.

with some lower intensity activity just as a warm-up and a cool-down, has been shown to improve fitness by almost 10% within two months. 10%? Just with like six 10-second runs? That's totally crazy. That's like two minutes of exercise a week. Yep. In 2022, we took a huge risk. We put our reputation on the line to prove that Zoe membership could improve the health of millions.

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simply go to zoe.com slash podcast. Okay, back to the show.

So this information is definitely useful for anyone who is time pressed. And our team did some research before this podcast. And what they found is that 80% of Americans do not achieve the CDC's exercise guideline, which is for at least 150 minutes of moderate intensity aerobic exercise every week. But I think what you're saying is they could increase the intensity of the exercise and actually get away with doing a lot less than 150 minutes. Is that right?

Yeah, these recent studies would suggest that would work. Yeah. So that's amazing and exciting, I think, for anybody who's really struggling with the time. But what about if I really don't like doing these intense bursts of exercise or maybe physically I can't, right? Lots of people may be listening to this who have restrictions.

but maybe I do have a bit more time on my hand, like what should I do? Yeah, so if the intensity is lower, then the duration needs to be longer. And even very low intensity activity has been shown to have a number of health benefits. And something just like fidgeting might even be enough. A recent study showed that just lifting your heel off the floor repeatedly whilst you're sitting down in your chair, just like you and I now,

can lower the rise in blood sugar after meals by as much as 50%. And one thing to bear in mind with intensity and time is that for the longer term changes in your health, a certain amount of intensity is probably needed.

Whereas the low intensity exercise gets you some of these immediate effects on metabolism, albeit not as long lasting. Amazing. So you've told me that I can either do a quite small number of short bursts of exercise like this, like 10 to 20 second sprints six times a week, or I can do a lower intensity exercise for longer. But how often do I need to do that? Is it every day, you know, a few times per week?

Well, we have an interesting study that looked at links between the amount and the intensity of exercise and cardiovascular mortality in nearly 4,000 people. These people were aged 40 years and over and were based in the US. And these were all volunteers who didn't have cardiovascular disease when they entered the study.

They wore a type of tracker called an accelerometer for a week, which is a device that measures movement. And Javier, is this a bit like a fitness tracker or a smartwatch? Yes, it is very similar. And so what did the study find? Well, they found that most people didn't do very vigorous exercise. And instead, those who met the CDC's exercise guidelines of at least 150 minutes of moderate intensity aerobic activity every week

achieved this mainly through activities like walking or cycling or even doing household chores or playing a sport. All the participants who were active enough to meet those guidelines still had a lower risk of all-cause mortality. And so that like lower risk of all-cause mortality in like normal speed basically means they were just less likely to die from anything. Is that right? Yes, exactly. Exactly.

And they were able to do that, you're saying, even without the high intensity exercise. So even just with, because in fact, you're saying not many people in reality were doing this. Despite this, people who were just walking more, maybe doing a little bit of sport with their friends or cycling, were having this really big impact on just being alive. That's right. So the lower intensity activity was enough to have this beneficial effect on their risk of death.

But what the researchers also found was that people who exercised more vigorously had an even lower risk than those who exercised more moderately. Brilliant. So, Javier, you've taken us on this tour of the topic. What's your verdict on cardio exercise? How much and how often should we be doing it? So, as I hinted at earlier on, something is better than nothing.

but more is better than less. So movement is key and doing it relatively frequently, trying to incorporate some into our daily routine can be helpful. And if we enjoy doing shorter amounts of exercise, then we should probably raise the intensity.

If we're not so keen on the intensity, then that's fine. We can still get a load of health benefits from exercise, but we probably need to do it either even more frequently or slightly longer in duration. So finding what works for you is probably key. And I think...

Life is also about compromises, right? I think about my own exercise regime, which is definitely driven by health benefits rather than the joy of going to the gym. I get no joy going to the gym and a great deal of joy at the end of the session knowing that I've finished it, haven't you? And so I end up going three times a week, which feels like an acceptable compromise because I just think I can't do more with Zoe and my family and all the rest of it. Is

Is that a good trade-off? Am I losing out massively by not going five times a week? No, that sounds great. We get most of the beneficial effects from going from very low or nothing to something. And then it's diminishing returns thereafter. So the three days a week, you're getting a whole load of health benefits there. And I guess the other thing I'd be keen for listeners to think about is that

Physical activity is more than just those exercise sessions in the gym. And there are small things we can do in our daily life to increase our overall physical activity. Things like taking the stairs or just increasing the number of steps we take throughout the day. And I was going to ask a bit about that because...

On the other hand, what's happened for me from the start of COVID and then continued is suddenly I do a lot more working from home than I did before. And I suspect there'll be quite a lot of people listening to this call who are also sort of at home more than before. How worried should I be about the fact that actually I'm basically sitting in this chair and I'm not doing the

the commute that I would have done before. I'm sure it's really early, so you're going to tell me there's not all the papers, but what's your sense? Yeah, like you said, I haven't seen hard evidence, but I would agree with you, at least my own experience of working from home from the office is my step count is always lower on a day working from home than working in the office without that commute.

as a practical message, I think we should probably be aware of that and try to incorporate some kind of movement throughout the day, maybe build it into your schedule in the time that you would be commuting if that's possible. I think it's really interesting. We should come back to specifically that topic because I think that it is harder to be

active. I'm definitely less active, but I've been starting to try and add things into my day to sort of force me to do things because it's really tempting. And the biggest plus for me is that my study where I'm sitting right now is at the very top of the house and the kettle is at the very bottom of the house. And as anyone who knows me knows, I'm completely addicted to

tea. So half a dozen times a day, I have to go all the way down in order to make a cup of tea. Exactly. That sounds like a great tip with the habit of making a cup of tea and you get a little goal at the end of it of a nice cuppa after you've walked down the stairs. Javier, thank you so much. If you've enjoyed today's podcast, and perhaps you'd like to learn a little bit more about how your exercise and your health works for you, you may be interested to try Zoe's personalized nutrition program.

You can learn more and you can get 10% off by going to joinzoe.com/podcast. I'm Jonathan Wolf. And I'm Javier Gonzalez. Join us next week for another Zoe podcast.