This is the BBC Sport Academy Fitness test and it works by calculating something called your VO2 Max.
This is the maximum amount of oxygen that can be removed from circulating blood and used by the working tissues and muscles during a certain amount of time.
It is a great way of measuring your fitness in long distance events or any kind of exercise which lasts longer than four to five minutes.
To achieve an accurate reading of your VO2, you can wire yourself to a computer and analyse the exhaled air by breathing into the apparatus.
Obviously this sort of equipment is not available to most people, so the following test is seen as a good estimate.
It will only be an accurate reading if the distance you have covered is 1 km or more.
What is a good or bad VO2 Max?
Top endurance athletes (eg: marathon runners) usually have a very high VO2 Max, usually measuring around 70 ml/kg/min.
The average person has a VO2 Max of around 35 ml/kg/min.
A low VO2 Max (25 or below) usually means you will be poor at endurance events.
The more endurance training you do, however, the higher your VO2 Max will become.