Why exercise?
The human body is designed for action. For most of the time that humans have been on the Earth they have had to keep busy to survive. In the Stone Age, people chased animals for food or dug up roots and gathered berries. They walked over large areas to find enough food to live and made shelters wherever they rested at night. Even when people settled down to farm the land, they had to keep active throughout the year. In winter the soil needed ploughing, in spring the seeds were sown and throughout the summer and autumn vegetables, fruit and cereals needed tending before harvesting. Rearing and caring for farm animals also meant an active life too.

Today, in many countries few people have to grow or find their own food. The invention of a wide range of farm machinery means that few people now need to work on farms. Many people now work in jobs where they do not have to move around very much. Their bodies do not get the exercise they need.

In the past, before the invention of television and computers, most children played outside. They played games such as hopscotch, hide and seek and tig, which involve a great deal of movement. Today many children take little exercise and watch television or play computer games in their spare time. These children do not get the exercise they need.

You may think that it does not matter that people do not exercise and that the rest may be better for them but this is not the case.

Nearly half the weight of your body is due to its muscles and they need exercise to stay healthy. If they do not get the exercise they need they will waste away. This will make you weaker so that when you want to move quickly for some reason, you will simply be unable to do so.

The most vital muscles in your body are those in your heart. In fact your heart is a bag of muscle with tubes that lead in and out of it. When blood enters the heart the muscles in the heart wall squeeze the blood and push it along blood vessels called arteries. In a healthy heart the muscles have enough power to push the blood round the body at rest and during vigorous exercise. If a person does not take enough exercise the heart becomes weaker and less able to cope when a quick movement is needed. In some circumstances the heart can fail completely and the person can die.

As if that is not enough, there is even more bad news for people who do not exercise. When we are at rest we only use the top part of our lungs for breathing. Dust and dirt can collect in the lower parts and gradually give the lungs an infection. During exercise all parts of the lungs are used and any materials that have settled in the lungs are blown out. Bones gain strength when the body exercises and weaken if the body is rested for long periods of time. This is especially important for children because the bones are growing. When children exercise the bones not only become strong but also grow correctly.

You can see that there are many answers to the question "Why exercise?" and all of them tell you one thing. If you are sitting around too much you must get out with your friends, play some games, find somewhere safe to cycle or go swimming. Your heart, muscles, lungs and bones are just waiting for you to make the effort.

What is tig?
It is a game that is best played by a number of people. One person in the group is elected to be 'on'. This means that they have the ability to tig someone. They do this by chasing after a person until they touch them with their hand. When they do this they shout, "Tig!" and the person who has been tigged is now 'on'. This person then tries to catch someone else or the tigger. The game continues for a certain amount of time or until everyone is tired.

What makes the sounds of the heartbeat?
The heart is divided into two halves and inside each half are two sets of valves. Each set opens and closes like a pair of double doors that you may have at the front of your school. The valves open to let blood pass through then close to stop the blood flowing back. They help the blood move in one direction round the body. One pair in each half of the heart is larger than the other pair. The two larger pairs in the heart beat together and make a 'lub' sound. The two smaller pairs of doors beat together and make a smaller 'dup' sound. When you put the two sounds together you have the familiar sound of the heartbeat ? 'lub' 'dup'.

How does the heart pump the blood?
The muscles in the wall of the heart work with the valves to pump the blood. The right half of the heart takes in blood that has travelled round the body and pushes it off to the lungs. The left half of the heart takes in blood from the lungs and pushes it off round the body. So the heart is really two pumps joined together. One pumps blood around the body and the other pumps blood around the lungs.

Is the pulse related to the heartbeat?
Yes, it is. When the valves in the heart slam shut they send a vibration down the tubes which are carrying the blood away from it. These blood vessels are called arteries. They are usually deep in the flesh but at certain points in the body they are nearer the skin and their walls can be felt. If an artery is touched with a fingertip the vibration can be felt as a pulse. Each heartbeat makes one pulse beat. If the heart is beating at seventy times a minute the pulse will be beating at seventy times a minute too.

Why can you not use your thumb to take the pulse?
The thumb also contains a pulse so a pulse in another part of the body cannot be felt.

What are the large blood vessels you can see under the skin?
They are veins. They carry blood back to the heart.

Are arteries and veins connected?
Yes, but not directly. When the blood leaves an artery it flows through tiny blood vessels called capillaries. These tubes take the blood close to all the cells in the body. Every organ and muscle has its own set of capillaries. There are even capillaries in the skin. When the blood has flowed through the capillaries it then flows into the veins and goes back to the heart.

Why do people sweat when they take part in exercise?
The blood carries sugar round the body. This is the form of energy that all parts of the body use. Muscles are full of blood capillaries. When the muscles are working they take sugar from the blood and use oxygen also from the blood to release energy. Most of this energy is used to make the muscles move but some of it is released as heat. The heat is carried away by the blood. During vigorous exercise a large amount of heat is produced. The body must keep its temperature constant if it is to stay healthy so the blood is allowed to pass through capillaries close to the skin. This makes the skin appear red. The heat in the blood passes into the skin. Some of the heat is lost by radiation into the air but the body produces sweat to get rid of most of it. Sweat is mostly water. The water absorbs the heat and evaporates taking the heat from the skin. Sweating is the body's way of allowing the body to exercise vigorously and still keep the temperature at a healthy level.