Fitness is the idea of having a body in which all of the organs are working properly.

Many organs in your body only work properly if they are worked hard. The muscles are an example. The heart is a muscle.

In the early days of humans, we would have to work hard just to find our food. Then, when we settled down, most of the time was spent working hard on farms, then in factories.

All of this meant that we got lots of exercise automatically. No one had to worry about keeping fit except for a few wealthy people, who just got fat and died.

But quite recently we have invented machines to do the jobs that we used to do by hand. There are bulldozers where once there were gangs of people with shovels. There are big combined harvesters in fields instead of thousands with scythes at harvest time. The list is endless.

At the same time we have become wealthier and so can afford to buy more food – especially meat.

So we eat more fat producing food and do nothing to burn it off. So we have to find some artificial alternative. We keep fit.

We would not have to exercise and go to gyms if we worked hard naturally, such as taking the dog for a walk or digging the garden or cycling to school. We still might want to exercise because we enjoy it, but we would not have to.