OF

PHYSICAL EXERCISE

ON FITNESS

OBJECTIVES

At the end of this topic you should be able to:-

1] Know the two types of exercise:-

a] STEADY

b] INTENSE

2 Know what happens to the body BEFORE, DURING and AFTER exercise.

3] Know about the production of ENERGY for exercise.

4] Know and understand about ATP.

6] Know how MUSCLES keep going during exercise.

7] Explain what happens to the body during exercise.

8] Know what the benefits are, of exercising.

INTRODUCTION

STEADY EXERCISE

Steady exercise is when sufficient oxygen can be breathed in to satisfy the needs of the muscles. Oxygen is required by the muscles to clear away waste products which are formed during the contraction of muscle.

During steady exercise the muscles use mostly fat for the creation of energy, but also glucose. As long as the glucose supplies last, the body can continue the exercise quite comfortably. However, when the glucose is all used then the body has to continue on fats alone. The effect of this is a build up of acid in the blood stream, and heavy sweating resulting in dehydration. The body cannot continue due to a raising of temperature and the person has to stop. If he attempted to continue he would eventually collapse and probably lose consciousness.

Once body temperature has dropped, then further exercise is possible but only for a very short time as the temperature will immediately start to rise again. It is important that a performer in this condition drinks some fluid as soon as possible.

INTENSE EXERCISE

In intense exercise, no fat is used because fat can only be used as a muscle fuel if there is a plentiful supply of oxygen. In intense exercise, all the oxygen is needed to try and clear away waste products. So in intense exercise the muscle fuel is nearly all glucose.

AEROBIC AND ANAEROBIC EXERCISE

These are the terms for steady and intense exercise.

STEADY EXERCISE ----- AEROBIC (with oxygen)

INTENSE EXERCISE ---- ANAEROBIC (without oxygen)

Intense exercise can in theory be performed without breathing. But if the performer doesn't breathe, then the oxygen debt will simply build up much more quickly.

GLUCOSE DOES NOT need oxygen to create energy needed for muscle contraction, but FAT DOES need oxygen.

1] BEFORE EXERCISE

In the period immediately before exercise, and even more so before an important competition, or event, a person will start to think about the exercise he is about to do. The more the mind is concentrated on the exercise the more the performer is said to be 'psyched up'.

When 'thinking about' exercise, hormones are released which prepare the body for action. The most important of these hormones is adrenalin.

Adrenalin is released into the bloodstream by the adrenal glands, and the effect is to stimulate the respiratory and circulatory systems. The rate of breathing increases and the heart beats faster.

2] DURING EXERCISE

Most of the cells of the body, but particularly the muscle cells, begin to work harder. Since a by-product of cell function is carbon dioxide, the amount of this waste product in the bloodstream is greatly increased during exercise.

The extra CO2 in the blood automatically stimulates the respiratory system to work harder to get rid of it - thus faster and deeper breathing results.

The hard-working muscle cells require an increased supply of oxygen to

(a) to combine fats to create energy, and

The extra oxygen is first taken in by faster and deeper breathing, and then second by the circulatory system moving the blood (which carries the oxygen) faster around the body. Thus, the respiratory system and circulatory system combine to transport oxygen to the muscles in much greater quantities than when the body us at rest.

During exercise, the heart rate increases from around 70 beats per minute to as much as 200 beats per minute. With each beat, the volume of blood pumped out increases from 100ml to as much as 200ml. Thus not only does the heart beat faster, but also it pumps out more blood with each beat. Combining these two factors produce an increase in the volume of blood pumped per minute form 5 litres to as much as 35 litres.

Yet another increase is in the amount of oxygen per 100ml of blood is dropped off at the tissues (including muscle tissue). There is always 20ml of oxygen in every 100ml of blood, but at rest only 5ml of this is used by the tissues. During exercise, however, 15ml is used.

Combining all these four factors together, i.e.

1] faster, deeper breathing

2] faster heart beat

3] greater volume pumped out with each beat,

4] 15ml/20 dropped off instead of 5ml/20, means that there is up to 30 timesas much oxygen available to the muscles than when they are at rest.

Another important effect of exercise, and another way in which extra oxygen can be transported to the muscles is the VASCULAR SHUNT. This refers to the way in which oxygenated blood is diverted from non-working areas of the body to working areas. During exercise the blood supply to the digestive system is reduced - hence the reason it is unwise to exercise after a large meal. The blood supply to the liver is reduced and the liver actually shrinks; this being a possible cause of 'stitch' pain when running. In severe cases of vascular shunts, the blood supply to the skin is reduced, making the skin go, pale and producing a tingling sensation, e.g. in the arms when long distance running. In exceptionally severe vases, the blood supply to the brain may be reduced - this will cause dizziness and force the athlete to stop the exercise.

During exercise, the body has to create extra energy to supply the needs of the working muscles. During light exercise this extra energy is supplied by a combination of stored body fat and oxygen, together with a little glucose. If the exercise is prolonged the glucose supplies stored in the body begin to run out. The exercise then has to continue on fats alone which results in a rise in body temperature, increased sweating, and dehydration forcing the exercise to eventually stop.

As the intensity of the exercise increases, the burning of fats alone cannot match the needs of the muscles. At rest, virtually no glucose is needed, in very light exercise very little glucose is needed, but as exercise becomes more vigorous then the more glucose is needed until in flat-out exercise the energy comes totally from glucose.

A by-product of the use of glucose for the production of energy is a substance called pyruvic acid. In medium or low levels of exercise there is enough oxygen present to oxidise this acid and dispose of it via the blood stream. However in higher levels of exercise, e.g. 400metre running, there is insufficient oxygen present to oxidise all the pyruvic acid and some of it will turn to lactic acid and remain in the muscles. After a very short amount of time, the build up of lactic acid is such that the muscles cannot function properly and the performer has to slow down to a point where the lactic acid build up can be halted and reduced.

Fat and Glucose comes from food. Excess glucose is stored around the muscles and in the liver in the form of glycogen. Excess fat is stored all over the body but particularly around the muscles.

3] AFTER EXERCISE

Heavy breathing and rapid heartbeat continues until all excess carbon dioxide and lactic acid has been cleared away.

The loss of water due to sweating will result in thirst.

Reductions in stores of glucose and fats will result in hunger, although this is not felt until respiration and heart rate have returned to normal, or near normal.

If a performer wishes to keep weight down, he must not refuel on fats, but should eat foods high in dietary fibre together with some carbohydrates (for glucose).

EATING FOR ENERGY

WHY DO WE EAT? ---- We need to eat for one basic reason.

WHAT HAPPENS TO THE FOOD WE EAT? - The digestive system breaks the food down into simple chemicals that the body can use. These chemicals pass into the blood stream and are taken to various parts of the body. The unusable part of the food passes through the digestive system and out of the body in the excrement.

CHEMICALS NEEDED BY MUSCLES

GLUCOSE --- A type of sugar, found in carbohydrate-rich foods.

FAT ------------ Visible (saturated) and invisible (unsaturated)

OXYGEN ----- Obtained by breathing, not from food.

These chemicals are carried to the muscle cells in the blood stream. Oxygen is either used or breathed back out, but glucose and fat can be stored until needed. Stored glucose is called Glycogen.

THE MUSCLES AT WORK

The muscles contract when the brain tells them to. The message to contract travels from the brain to the muscle along the nerves. The message is called a nervous impulse.

HOW THE MUSCLE CONTRACTION IS TRIGGERED OFF

When the nervous impulse reaches the muscle, the nerve actually goes into the muscle. At the end of the nerve (inside the muscle) the impulse causes a tiny electrical charge to be given off. This charge sets off a chemical reaction in the muscle cells which results in the muscle contracting.

WORK AND ENERGY

Any work requires energy. When muscles contract, they are working. This work requires energy, and the energy is provided by the chemical reactions which take place inside the muscle.

This is a chemical which is vital to muscle contraction. Without ATP there can be no contractions. ATP is always the end product of the chemical reactions which take place in the muscle.

Small amounts of ATP are stored in resting muscles ready for use. But if muscle contractions carry on for more than a few seconds, then ATP has to be continuously formed and re-formed for as long as the work continues. This is where glucose, fats and oxygen become important.

The following figure deals with the different ways that ATP can be produced, using glucose, fats and oxygen. It will look at how muscles keep going - known as muscular endurance.

MUSCULAR ENDURANCE - How the Muscles Keep Going

Muscles can only contract if there is ATP present. Therefore to keep a muscle working, ATP has to be continuously formed and re-formed.

WHAT HAPPENS TO THE ATP...?

When ATP is used by a muscle, it is broken down to ADP.

Or ---- Adenosine Triphosphate becomes Adenosine Diphosphate.

So:- ATP -------- MUSCLE CONTRACTION --------- ADP

WHAT HAPPENS WHEN ATP STORES RUN OUT?

Muscles only have very small amounts of ATP stored ready for use. For example, a sprinter has enough for only about one second of explosive effort. After that ATP has to be re-formed.

1] THE CP SYSTEM

CP stands for Creatine Phosphate. Thus is another chemical which is stored inside muscles. It can combine with ADP to form fresh ATP. The CP system is extremely efficient - no oxygen is required and there are no waste products left afterwards.

BUT --- the muscles can only store enough creative phosphate to last for between 5 and 10 seconds of intensive activity.

So if the activity lasts longer, the body has to switch to a different system of energy production (or ATP production).

`2] THE GLUCOSE/LACTIC ACID SYSTEM

When the Creatine phosphate has run out, the muscles then call upon their stores of Glycogen. (remember that glycogen is stored glucose).

Just like Creative phosphate, glycogen can combine with ADP to form fresh ATP.

BUT --- There is a side-effect. When energy is produced from glycogen, a waste product called Pyruvic Acid is left behind. If there is enough oxygen around, then the pyruvic acid is changed into carbon dioxide and water, and there is no problem. This would be the case in low levels of activity.

In more intense activity, more pyruvic acid is produced, which means more oxygen is needed to clear it away. But the lungs and heart can only get a limited amount of oxygen to the muscles, and in very vigorous activity it is not enough. Some of the pyruvic acid would then change into Lactic Acid. Once this starts to build up in the muscles, then muscular contractions become very difficult and painful, until eventually they become impossible.

3] THE AEROBIC (GLUCOSE/FATS/OXYGEN) SYSTEM

This system is used during lower levels of activity when there is enough oxygen being delivered to the muscles to oxidise (clear away) all the pyruvic acid, and therefore, prevent a build up of lactic acid.

At lower levels of activity, fats can be used as a muscle fuel to make ATP. The body will use fats so that its stores of glycogen can be preserved as long as possible, but some glycogen is always used. As a general rule, the more intense the exercise, the more the glycogen is used rather than the fats. Also important to remember is that the longer the exercise goes on, the more that fats have to be used because the glycogen is running out.

PHYSIOLOGICAL BENEFITS OF EXERCISE

There are many ways in which the body benefits from a regular programme of physical exercise.

1] INCREASE IN TOTAL VOLUME OF BLOOD

If there is more blood in the body, there will be more haemoglobin, and therefore, more oxygen when it is needed e.g. during exercise. So there is greater endurance.

2] CAPACITY OF THE LUNGS INCREASE

More air can be breathed in and more air can be breathed out. This means that more oxygen can be breathed in (when needed) and more carbon dioxide can be breathed out.

3] HEART MUSCLE GROWS IN SIZE AND STRENGTH

With each beat, or stroke, the heart will pump out more blood. This means that at rest the heart rate of a fit person will be lower than an unfit person. Also in hard exercise the heart will pump out greater quantities of blood in a fit person. Another way of putting it, is that whatever the level of exercise, and whatever the body's oxygen requirement, the fit person will need less beats of the heart to meet the requirement than an unfit person. This increase in blood pumped out per beat is called an increase in 'stroke volume'.

4] REDUCES HEART'S WORKLOAD

This follows on from (3). If the heart does not need to beat as often, it will probably last longer which could mean a longer life.

5] PROTECTION FROM HEART DISEASE

Harmful Cholesterol, which is found in meat and animal produce (milk eggs and butter) will not build up in the coronary arteries of a fit person as much as an unfit person. Cholesterol in the coronary arteries can cause fatal heart attacks. (Coronary arteries are those arteries which deliver blood to the heart muscles).

6] INCREASE IN CAPILLARIES

Regular exercise results in an increase in the number if capillaries between each artery and vein. More efficient exchange through the capillary walls of oxygen for carbon dioxide and muscle fuel for waste products. Another way of putting it, is that 'Tissue Respiration' will become more efficient.

7] BLOOD SUPPLY TO HEART INCREASES

Due to increase in capillaries around heart muscle. This makes heart stronger and more efficient.

8] PROMOTES BONE STRENGTH AND THICKNESS

A physically fit person will have stronger and slightly thicker bones than an unfit person. This means the fit person will be more resistant to breaks. He will be able to take much harder blows, e.g. rugby.

9] KEEPS WEIGHT DOWN

But only with a sensible diet. Exercise does burn off calories, but it is very easy to put them all back on again.

10] PERFORMANCE IN SPORT WILL IMPROVE

Due to an improved 'Aerobic Base'. The aerobic base is a person's basic level of aerobic fitness. If a person has basic fitness he will perform better in sport. A footballer may have superb ball skills, but if he is unfit he will not be able to use them in an competitive match.

11] LESS FATIGUE MEANS LESS INJURY

Many injuries in sport occur towards the end of the game when a player is fatigued. Therefore, the fitter the player, the less likely he will be to suffer injuries.

SUMMARY OF BENEFITS OF EXERCISE TO THE CIRCULATORY SYSTEM

1] INCREASE IN BLOOD VOLUME

2] HEART MUSCLE BIGGER AND STRONGER

3] HEART MUSCLE BETTER SUPPLIED WITH BLOOD

4] HEART'S WORKLOAD REDUCED

5] LESS CHANCE OF HEART DISEASE

6] INCREASE IN CAPILLARY NETWORK SO MORE EFFICIENT EXCHANGES

(Improved Tissue Respiration)

To keep the muscles working, the body has to continually make a substance called ATP. When ATP is used to make a muscle contract, a substance called ADP is left behind.

Resting muscles have a very small supply of ATP stored in them but in a cross-country, this would be used up as the athlete is warming up on the start line.

Energy for the first few seconds of the run is provided by Creatine Phosphate system or CP system.

In the CP system fresh ATP is made by a combination of the leftover ADP and CP. Small amounts of CP are stored in the muscles and these stores will provide fresh ATP for between 5 and 20 seconds. This time will vary according to the fitness of the athlete and also the speed at which he is running.

During the CP stage the athlete will feel quite comfortable. The CP system does not need extra oxygen so an increase in respiration is not needed. Also the system does not leave waste products behind to clog up the muscles so the body is able to move very freely and comfortably. So the CP system is an extremely efficient one.

As long as supplies of CP last, then the runner is able to continue quite easily. But after 5 to 20 secs, the CP system begins to break down. The muscles then have to find an alternative source of energy - they have to find a new way of making ATP, so, that the athlete can continue running.

Around the 45 second mark, the body feels as if it is struggling to cope with the switchover to aerobic work, but eventually the respiratory and heart rate will become high enough to cope with the threatening build-up of pyruvic acid. However, while the body was making this adjustment, some of the pyruvic acid will have been turned into Lactic Acid which collects in the muscles and make the run very difficult. But this is soon cleared by the extra oxygen and soon a steady state is reached where the amount of extra oxygen being delivered to the muscles is just enough to prevent any build-up of lactic acid. This steady state will be reached at somewhere near the 2minute mark.

Another change taking place between the 1 and 2 minute mark is the adjustment from using glycogen to using a combination of fats and glycogen. This happens during cross-country running so that the muscle's glycogen stores can be made to last as long as possible. If the body used all the glycogen in the first part of the run, it would then have to switch to using fats alone and this would lead to sweating, and dehydration. So it is important during the early part of the run to find an economical balance of glycogen and fats.

So to summarise, the first 20 seconds of the run is fuelled by the CP system which is an anaerobic system. Then the Aerobic systems take over using oxygen, glycogen and fats to fuel the muscles. The end-product of both systems is the essential element of energy production - ATP.

USING THE BOOKLET TO HELP YOU, ANSWER THE

FOLLOWING QUESTIONS IN SENTENCES.

1] WHAT IS A NERVOUS IMPULSE?

2] WHAT IS GLYCOGEN?

3] WHAT DOES ATP STAND FOR?

4] WHAT DOES WORK ALWAYS REQUIRE?

5] WHAT ARE THE TWO TYPES OF FAT?

6] WHAT IS THE BASIC REASON FOR EATING?

7] WHERE DOES OXYGEN COME FROM?

8] WHAT HAPPENS TO THE UNUSABLE PARTS OF FOOD?

9] WHEN DO MUSCLES CONTRACT?

10] WHAT DOES THE DIGESTIVE SYSTEM DO TO FOOD?

11] WHAT HAPPENS TO UNUSED OXYGEN?

12] WHAT FOODS CONTAIN GLUCOSE?

14] WHAT CHEMICAL IS ALWAYS THE END-PRODUCT OF ENERGY PRODUCTION?

15] WHAT IS GLUCOSE?

19] WHAT HAS TO HAPPEN INSIDE MUSCLES IF CONTRACTIONS ARE TO BE MAINTAINED FOR A LONG PERIOD OF TIME?