Interval training involves alternating high intensity bursts of activity with lower intensity stages of recovery. Because the body's aerobic and anaerobic systems are overloaded at the same time, you get the benefit of training both at once.

As a high intensity training method, it is certainly harder work than lower intensity training, but the benefits can be seen much more quickly.

How interval training works.

The interval training technique can be applied to pretty much any exercise, e.g. running, rowing, swimming, cycling etc. Taking running as an example, you'd start with the usual warm-up for 5-10 minutes at a low to moderate intensity. Then increase the pace to a sprint for one minute. At the end of the minute, lower the intensity by slowing down to about half the speed to allow your body to recover. Stay at this rate for about 2 minutes before starting the next high-intensity minute. Keep alternating these two periods.

Depending on your fitness level, you might not want to push yourself too hard during the higher intensity periods at first. However, you'll quickly find that your fitness improves and you'll soon be able to increase the speed or duration of the high intensity bursts.

Some exercise machines such as running, cycling, rowing machines and elliptical trainers have an interval training setting as one of the built-in programmes. They'll allow you to set two speeds or resistance levels and press a button to toggle between the two. If the machines at your gym don't have interval training pre-programmed, you can simply change the speed or resistance setting manually.

Don't think that interval training has to be confined to machines in the gym either. If you prefer exercising in the great outdoors, this training method is easily employed in activities such as running and cycling simply by speeding up and slowing down.

The science behind interval training The intensity of the high intensity bursts should be high enough that you would not be able to maintain them for long. During these periods, your body will use the anaerobic system for energy, the by-product of which is lactic acid. Lactic acid builds up in the muscles causing the 'burn' and creating what is referred to as an 'oxygen debt'.

During the lower intensity periods, the heart and lungs must work to repay the oxygen debt by delivering oxygen to get rid of the lactic acid. This period trains the body's aerobic energy system. The trick is, not to slow down too much during the lower intensity periods; you don't want the heart rate to drop too much otherwise the aerobic training effect is reduced.

What are the benefits of interval training?

Alternating your intensity is far more interesting than exercising at the same intensity for long periods of time. As it is more intense overall, you'll also burn more energy in less time. This means your workouts can be shorter and more fun and still burn more fat.

Working at high intensity also stimulates your metabolism, so that after you finish your workout, you'll continue to burn fat at a higher rate than if you'd exercised for longer at a lower intensity.

The cardio-vascular system is trained more quickly doing this type of training compared with longer periods of lower intensity exercise.

Long duration endurance training is often associated with injuries because of the repetitive stresses placed on joints and soft-tissues. Because interval training is less repetitive, it is a good way to reduce risk of these types of injuries.