Indoor Sport Services Training Guide

Whatever you are doing, whether you are running a marathon or lying in bed you require energy. If you do nothing at all, then you only require a very small amount of energy to keep you alive. This is called the basal metabolic rate (BMR) and is the minimum amount of energy that your body can survive on. Anything that you do adds to your energy requirements. Any kind of exercise or movement requires energy so it follows that the body must be able to provide for these energy requirements. This section of the guide will explain how the systems that produce energy in the body work, the fuels that they require and the systems that supply those fuels and remove the waste products.

The Energy Systems

To produce movement the body must break down an energy store to release energy in a form that it can use. The energy store that the body requires to release this energy is called adenosine triphosphate (ATP). When the body breaks down the ATP the energy released is in a form that can be used to create movement.

The Anaerobic System

The anaerobic system has two energy pathways, the phosphocreatine, creatine phosphate or alactic system which provides very rapid release of ATP but only lasts for ten seconds, and the lactic acid system which is slightly less rapid but lasts for up to four minutes.

The alactic system relies on the substrate creatine phosphate that is stored in the muscles and because of its short duration is the main energy source used by 100m sprinters and weight lifters. After high intensity exercise your creatine phosphate levels will be depleted and can be resynthesised using energy from glycogen metabolism.

The lactic acid system breaks down glucose, or glycogen (stored sugar), to produce ATP. It comes into use immediately after the alactic system and can produce enough ATP for up to four minutes of high intensity exercise, but peaks at one minute. For this reason a 400m runner or 100m swimmer relies heavily on this system for their energy. Unlike the alactic system the lactic acid system leaves behind a by-product, lactic acid. Lactic acid causes the muscles to become more acidic, work less efficiently and causes the muscular pain that we associate with exercising hard. Therefore we try to minimise the production of lactic acid wherever possible.

The Aerobic System

The aerobic system is the slowest of the three systems to work but has the advantage of lasting indefinitely. This is the system that produces the energy required for the BMR and any non-sprinting movement that takes place throughout the day. Like the lactic acid system the aerobic system can use glucose or glycogen as its fuel but can also use fat, which produces much more ATP. The aerobic system is able to produce 19 times more ATP from each molecule of glucose than the lactic acid system can but has the disadvantage of requiring oxygen so takes as long to start as it takes the oxygen requirements of the cell to be catered for. For this reason the aerobic system does not take over from the lactic acid system for approximately three minutes. When fat is used as the fuel for the aerobic system it produces much more energy than glucose or glycogen but requires even more oxygen and so it can take between 20 and 40 minutes for fat to take over as the main fuel as it takes this long for the oxygen requirement to be met.

How Do the Fuels Get to the Muscles?

There are two body systems responsible for supplying the demand of fuels for the energy systems. These are the respiratory system and the circulatory or cardiovascular system.

The Respiratory System

The respiratory system consists of the lungs and respiratory muscles (the muscles of the chest wall, the abdomen and the diaphragm). The main job of the respiratory system is to inhale air, allowing the oxygen in the lungs to diffuse into the blood and the carbon dioxide in the blood to diffuse into the lungs to be exhaled. The oxygenated blood can then be transported around the body through the cardiovascular system.

The Cardiovascular System

The cardiovascular system consists of the heart and blood vessels. It is responsible for circulating the blood through two circuits. The first pumps the deoxygenated blood from the right side of the heart to the lungs where it becomes oxygenated as the oxygen bonds to the haemoglobin molecules in the red blood cells. The oxygenated blood then returns to the heart. The second circuit pumps the oxygenated blood from the left side of the heart around the body. Because the left side of the heart has to pump the blood further it is more muscular than the right side. The blood is pumped through the intestines and stomach where it collects nutrients and then to the muscles or organs. It then travels to the cells where it releases the nutrients and oxygen and collects the waste products and carbon dioxide and returns to the heart. The cycle then starts again.

During exercise the heart rate increases in response to demands for increased blood flow. This controls the body temperature and the supply of oxygen and nutrients to the working muscles. During heavy bouts of exercise the amount of blood flowing at any given time can increase by a factor of seven as a result of increased heart rate and stroke volume. Heart rate increase is initially linear and directly proportional to exercise intensity.

The blood plays a very important part in both supplying the fuels and removing the waste products of energy synthesis and in the maintenance of homeostasis (maintaining the body at balance). It is composed of 55%plasma of which 90% is water, 44% red blood cells (erythrocytes) and about 1% of white blood cells (leukocytes) and platelets (thrombocytes). The red blood cells have the haemoglobin molecules which bond with oxygen and allow the transportation of oxygen, the white blood cells fight infection, the platelets allow clotting in the case of a cut or abrasion and the plasma supplies water to the cells and helps to maintain the body temperature. If there is a shortage of any of the constituent parts of the blood the body is not able to function properly. If there is not enough haemoglobin or red blood cells the person may feel weak. This is called anaemia and is common both in pregnant women and in endurance athletes. It is caused by a lack of iron, the important part of the haemoglobin molecule, and can be easily cured with an iron supplement. If you think you might be anaemic then you should visit your doctor for professional advice.

VO2 Max

When exercising the level that we can work at is normally limited not by the fuel stores in the muscle but by the maximum amount of oxygen that the body can take in and utilise in any one minute. This is called the VO2 max. VO2 max is limited by the amount of blood that can be pumped through the lungs and to the working muscles and by the efficiency of the lungs. The maximum value possible for a person's VO2 max is capped by their genetic make up but the right training can help you achieve your potential. (A test to calculate your VO2 max is given in Physiological Tools in Section 3 : Physiology).

The Effects of Training on the Body

The effects that training has on the body is dependent on whether the training undertaken is aerobic or anaerobic so these effects will be explained in two sections.

Aerobic Effects

By following an aerobic training programme for as little as 12 weeks you can make significant improvement in your VO2 max. This is possible because you have made some physiological changes to the parts of the body that limit your VO2 max. The heart responds to aerobic training like any muscle does to work: by getting bigger. This is called cardiac hypertrophy and results in an increase in the amount of blood that can be pumped out in each beat (the stroke volume) and hence an increase in the amount of blood that can be pumped in one minute (the cardiac output). This change to the heart means that the heart needs to beat fewer times to move the same amount of blood, therefore your resting heart rate will decrease. The lungs are also affected by aerobic training. They become more efficient and are able to take in more air per breath and take more breaths per minute. The final changes that occur due to aerobic training is that your blood volume increases due to an increase in blood plasma and red blood cell volume and the muscles become more efficient due to an increase in the ability to transport oxygen within the cell and to respire (resynthesise ATP).

Anaerobic Effects

The changes that take place in the body due to anaerobic training are limited in number compared to those that take place due to aerobic training. This is because many of the changes caused by aerobic training are an improvement in the ability to carry or utilise oxygen. In anaerobic training this system is not required so the adaptations are limited to four major points;

1. Muscle hypertrophy - the muscles used in high speed activities (the fast twitch muscle fibres) will increase in size.
2. Enzyme activity increases in the enzymes that are responsible for anaerobic energy production and recovery from anaerobic activity.
3. Energy stores of the anaerobic energy sources, ATP, phosphocreatine and glycogen increase in size.
4. Lactic tolerance - fast twitch muscle fibres become more tolerant to increased levels of lactic acid.

The changes outlined above show that it is very important to know what changes you wish to take place in the body before you start training so that you can ensure that you are doing the right sort of training to promote the improvements that you require.