Key Idea 4

The lungs and heart are very important for exercise. Oxygen is useful for creating energy for our muscles to use. We can create energy that our muscles can use without oxygen and with glucose alone (pure energy) but this is called anaerobic respiration. This is bad for your body because it creates lactic acid in the process. This is toxic for your cells and is what causes cramp and some other muscle pains after exercise.

Your body gets oxygen from the air around it. This is called aerobic respiration. During this process, oxygen and glucose turn into carbon dioxide (the air you breathe out), water and energy for your muscles to use. This oxygen and energy is transported by your body to your muscles in your blood.

Air gets to your lungs through the trachea (windpipe). The trachea divides into two bronchi, with one bronchus for each lung. Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area and speed up the absorption of oxygen. You breathe in and out because your diaphragm contracts and expands. When your diagrahm contracts there is less room in your lungs and so carbon dioxide is pushed out. When it expands, there is more room for oxygen so you breathe in. Arteries then take the oxygen in your blood around the body before deoxygenated blood returns to the heart in veins.

A person's heart rate and breathing rate go up during and after exercise. This is because your body needs more and more oxygen to get the energy to your muscles. Your body is fitter and more efficient if it has bigger, faster lungs and hearts because then it can use as little effort as possible to transfer energy to your muscles.

Because of this, athletes sometimes do altitude training, where there is less oxygen in the air. This is so that their body is used to operating with less oxygen and so when they are playing/performing, they can get energy to their muscles easier.