The heart lies at the centre of the cardiovascular system, which also comprises the lungs and the circulatory vessels, ie veins and arteries.

One of the major roles of the cardiovascular system is to provide oxygen to the muscles.

For only when oxygen is present, can the muscles release the bulk of their stored energy.

The more oxygen that the cardiovascular system can supply the greater the body's capacity for endurance events like running, swimming and cycling.

The word aerobic means "with oxygen," which is why this type of activity is called aerobic exercise.

Your aerobic fitness is usually measured in terms of the maximum amount of oxygen you can supply to your muscles, which is referred to as your V02 max.

In order to improve the efficiency of the oxygen delivery system, it is necessary to elevate your heart rate to between 60 per cent and 85 per cent of maximum, for a period of 20-30 minutes.

Eventually the heart will become stronger.

The amount of blood it pumps out with each beat will increase, and the substance in the blood which attracts oxygen, called haemoglobin, will also multiply.

You will be able to work for longer at higher intensities, without fatiguing. In other words, you will get fitter.

I addition to an increase in aerobic capacity, you will also burn body fat, lower cholesterol levels and feel an increase in energy.

Clearly, the value of cardiovascular conditioning is enormous, and the benefits can be yours in exchange for 30 minutes of your time three times a week.