All About Cardio Fitness

Here’s a brief overview of cardio fitness and training. I advise all my personal training clients in London to include some aerobic training in their weekly exercise regime. Yes, aerobic training and cardio training are essentially the same thing. As a personal trainer, I include cardio-boxing in most of my sessions with my London clients, sometimes running too.

running woman

running woman


My Chambers Dictionary has a great definition of aerobic exercise:

“Exercising by means of such rhythmic activities as walking, swimming, cycling etc in order to improve physical fitness through increased oxygen consumption.”

The key here is oxygen. This is the key component of energy production and human survival, together with food and water. Increasing your aerobic fitness is about increasing the efficiency of your heart, lungs, and blood vessels to absorb and transport oxygen to all the cells of your body. Your ability to do this is known as your ‘aerobic capacity’.

The most simple measure of your cardiovascular fitness is your resting pulse rate, or heart rate. This is measured in heart-beats per minute. If you’re extremely fit, this is anything between 40-60 beats per minute. Most people are in the region of 60-75 beats per minute. ¬†If you’re unfit, it will be more like 75-100 beats per minute.

‘Stroke volume’ is the amount of blood your heart pumps per beat, and the higher your stroke volume, the stronger and more efficient your heart, and the fewer beats per minute you need to transport a given amount of oxygen around the body.

‘Cardiac output’ is the volume of blood your heart pumps per minute. This is your stroke volume multiplied by number of beats per minute. The higher your cardiac output, the fitter you are. Your heart is a muscle, the most important muscle in the body, and the more you exercise it the stronger it gets.

Another associated definition is ‘cardio-respiratory endurance’, which brings the lungs into the equation. The greater your lung ¬†capacity, the more oxygen you can absorb from the lungs into the bloodstream.

Measuring the efficiency of your lungs

There are 3 measures of lung fitness:

Peak Flow: the maximum force at which you can expire your breath, measured by a peak flow meter, and measured in litres of air per minute (L/min). The fewer constrictions you have, the better your peak flow. If you smoke, or have asthma, or generally unfit, your peak flow will be compromised.

Lung Function: there are two measures of lung function, FVC, and FEV1.

FVC: This is the capacity of your lungs, from one maximum inhalation to one maximum exhalation, in other words your lung capacity, how much air you can take in.

FEV1: this is the volume of air you can exhale in the first second of your maximum exhalation, so it’s linked to your lung capacity and your peak flow. FEV stands for forced expired volume.

Measuring your cardiovascular fitness

The key measure is VO2 Max, which measures your maximum oxygen processing capacity. For most people this is measured by estimating VO2 max with sub-maximal tests. Most people are too unfit to safely push them to their maximum aerobic capacity, hence a range of sub-maximal tests to suit various levels of starting fitness.

These sub-max tests measure your oxygen consumption at lower levels of aerobic exercise.

There’s the ‘one mile walk test’ which measures your heart rate at the start and end, and takes into account your speed. Then there’s the Chester Step Test, devised by the human performance lab at University College Chester. This is where you step on and off a 30cm high step at various rates per minute, and your heart rate is measured every 2 minutes.

The true VO2 max test takes you to your aerobic capacity, and this is measured by a sophisticated piece of kit called the SRM Ergometer. It looks like a stationary bike, but meaures power output with laboratory accuracy. It’s linked to a computer, and an on-line gas-mass spectrometer to measure oxygen content of your exhalations, captured by a gas-mask. And of course, your heart rate is monitored constantly.

So the volume of oxygen you consume during each minute of the test is measured, and also how much power is being produced for each litre of oxygen consumed. And this is measured right up to your maximum heart rate, something most people never experience, and believe me, it’s gruelling.

When you’ve reached your aerobic capacity, you’re at the threshold where your anaerobic energy system (lactic acid system) starts to take over from your aerobic system, the point at which you start training ‘anaerobically’ (without oxygen). This is where you reach the point of physical exhaustion.

Bath University’s Human Performance Centre has some of the best VO2 Max testing facilities in the country, and this is where elite athletes and sports people go to be tested.

Frequency, intensity, and time

As a personal trainer, my London clients ask me how much cardio they should do each week. I recommend a frequency of 3 times a week, for 20-30 minutes per session, at an intensity that’s appropriate for your current fitness level.

Intensity is measured by your heart rate. Your ‘optimum training zone’ is between 60-85% of your maximum heart rate, which is estimated as 220 minus your age. So for example if you’re 40 years old, your estimated maximum heart rate is 180 beats/minute, and you should be training with enough intensity that your heart rate is at least 108 bpm (beats per minute) but not over 153 bpm. And you maintain this range for 20-30 minutes.

The benefits of cardio exercise

There’s a myth that cardio exercise is the best way to burn fat. Although you will burn some fat during your cardio sessions, this is not the most effective exercise for fat burning. Resistance exercise with weights, which build muscle, is the best way to burn more fat long term, because it increases your basal metabolic rate 24 hours a day, and a higher proportion of fat vs carbs is burnt at rest.

So the main benefits of cardio are: increased strength and health of your heart and lungs, your whole cardiovascular system (all the blood vessels throughout your body, right down to the tiny capillaries). Other benefits include bone health, hormonal balance, blood pressure regulation, mental health, and cognitive function.

Different types of cardio exercise

My next blog post will explore different types of cardio exercise, everything from running, cycling, cardio machines in the gym, and cardio-boxing. I’ll give you some tips on technique, and ways to make your sessions more fun and effective too.

(Dominic Londesborough is a personal trainer in London with over 10 years experience)