What is cardio?

Cardio is short for cardiovascular, which is the system in your body run by your heart and lungs. So cardio exercise refers to exercise which raises your heart rate and your breathing rate over a period of time. There are different forms of cardio training, which we will explore later, but that’s a basic description. You might also hear Cardio being described as aerobic exercise or endurance exercise. You might traditionally think of running, swimming or cycling as cardio workouts, but technically it could be anything that gets your heart rate up – so dancing, gardening or even vacuuming could be considered a cardio workout. Depending on how dirty your carpets are…

Technical bits – the cardiovascular system

The cardiovascular system involves your heart and lungs. This is the system responsible for the circulation of blood around your body. When you breath in, the lungs take in oxygen, which is transferred to the blood. The heart then pumps this oxygenated blood around the body. Once the blood has done its job, it returns to the heart, which pumps it back to the lungs to get more oxygen so the cycle can start all over again. The volume of the lungs depends on the individual, and can be changed by regular exercise – in other words if you do cardio exercise on a regular basis your lung capacity will increase and your lungs will get better at their job. Similarly, your heart is a muscle, and as with any muscle if you train it, it will get stronger. As it does so, it can pump a greater volume of blood in one go, and therefore needs to beat less often. This is why endurance athletes who train cardio a lot have very low resting heart rates. This is only one of many, many benefits cardio exercise brings, which we’ll look at later.

The different levels of cardio workouts

The mention of heart rates brings us nicely to the different levels of cardio workouts. These are generally defined by how hard your heart is working, as a percentage of your maximum heart rate (maxHR – the highest number of beats your heart can do in one minute), or by how hard you feel that you’re working as per the Rate of Perceived Exertion (RPE) scale:

The RPE is a good scale to use for beginners or people who are not used to exercising as it is easy to follow and it is individual to you – what I think sits as a 7-8 effort might be a 4-6 effort for someone else. That’s not to say it’s only for beginners though! The RPE scale has the other advantage of allowing you to judge your workout based on your circumstances at that exact time – you might do a workout on a Monday morning and feel amazing because you’re rested and enthusiastic, but if you do that same workout on a Friday afternoon or after a nightshift you might feel absolutely knackered and can’t be bothered. The RPE scale allows you to work at the intensity that your body can cope with at that exact time.

In terms of heart rates, these are often split into ‘zones’ which define how difficult the exercise is and how hard your heart is beating. This is most easily explained by way of an image. This first one shows four training zones as a percentage of your maxHR:

Now, before I go any further, it’s worth noting that heart rate zones can be quite difficult to work out without proper testing. There are a number of formulae on t’internet that will help you to work out your maximum heart rate (for example the basic 220 – your age) but these will only give you a rough estimate and do not take into consideration your individual circumstances. There is also a bit of debate around ‘training zones’ themselves and how many there are, and what percentage of heart rate they cover, and what each zone is good for, etc etc. My advice for those starting out would be to use RPE, and if you get to a stage where you want to use HR to train, do some research and find a formula to work out your maxHR that is relevant to you, then find a set of training zones that also make sense to you and stick to it. I’ve given the four-zone example above as an illustration because it’s simple and easy to follow, but you’ll see some with up to six zones mentioned.

It’s also worth highlighting that if you’re looking up information on cardio or HR zones you’ll likely see a lot of references to the ‘fat burning zone’’. This most-often refers to light-to-moderate exercise, sometimes called zone 2 depending on the zone system used, or usually around 50-70% maximum HR. It’s referred to as the fat-burning zone, because at this exercise intensity the body uses its fat stores as its primary fuel. So it logically follows that if you exercise at that intensity all the time you’ll simply use your excess fat as fuel and burn it all off… Doesn’t it?

Well not quite. While it’s absolutely true that when exercising at a lower intensity the body uses fat as fuel, it’s also true that exercising at a lower intensity also uses less energy overall. Let’s say I do a brisk walk for half an hour. I’ve used fat as fuel and maybe burned 100 calories. However if I run for half an hour, while my body has likely changed from using fat for fuel to using glycogen for fuel as my heart rate rises, I’ve also used more calories, let’s say 250 calories. To say nothing about the after-effects on the body of more intensive exercise (which I won’t, because I keep going off on tangents). As it’s overall energy expenditure (calories burned) that governs weight loss then if that’s my goal then the run is likely going to help me more than the walk, regardless of the fuel source my body is using.

Anyhoo, we digress.

I mentioned earlier that two of the benefits of cardio exercise were strengthening your heart and lungs. Regular aerobic exercise has a number of other benefits, including reducing blood pressure and cholesterol, and therefore your chances of having a heart attack or a stroke. It also decreases your risk of developing Type 2 diabetes and various types of cancer. There are various studies that demonstrate that regular exercise is a great tool for preventing or countering depression. Weight-bearing exercise such as running can help prevent bone density loss and therefore osteoporosis. All of this information can be confirmed on the UK National Health Service website if you don’t believe me (Benefits of exercise – NHS).

So how much should I do? What’s “regular”?

Well, both UK and US guidelines suggest that adults (18-64) should do 150 minutes of moderate intensity exercise per week. So divided by 7 days that’s just under 22 minutes per day. Their definition of moderate intensity is a brisk walk. While they’re not prescriptive about how you achieve the total of 150 minutes, they do suggest trying to spread exercise evenly over at least four days. But the more the merrier!

Alternatively, instead of 150 minutes of moderate exercise, 75 minutes of vigorous exercise is also suggested. Again this should be spread out over t least four days. Vigorous activity examples provided are running, swimming, or sports like hockey or netball.

As I said right back at the start though, it’s anything that raises your pulse and your breathing rate. It might be following along with a YouTube aerobics video in your front room, or skipping in your back garden. Or dancing. Or anything you enjoy that gets you moving really, because that’s how you’ll stick with it. It doesn’t need to be fancy or need expensive kit.

To quote the UK Chief Medical Officers, “For good physical and mental health, adults should aim to be physically active every day. Any activity is better than none, and more is better still” (UK Chief Medical Officers’ Physical Activity Guidelines)

Ok, so I should do cardio?

Yes.

There’s a current social media trend which says the only exercise you need is strength training. While this is important (and the topic of my next post) you should also be doing cardio. Strength training is very good for you, and very necessary, but it does not bring the benefits to your cardiovascular system (and therefore all the related benefits to your body and health) that aerobic exercise does. It’s not a case of one or the other. Do both. For all the reasons benefits listed above, do cardio. Include it in your workout schedule. Please.