Run for Your Life

• Skeletal muscles are made up of large bundles of long cells called muscle fibres.
• The cell membrane of muscle fibre is called the sarcolemma.
• Parts of sarcolemma fold inwards across the muscle fibres and stick into the sarcoplasm (a muscle cells cytoplasm). These folds are called transverse (T) fibules and they help to spread electrical impulses through the sarcoplasm.
• A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm. the sarcoplasm reticulum stores and releases calcium ions that are needed for muscle contraction.
• Muscle fibres have lots of mitochondria to provide ATP thats needed for muscle contraction.
• Muscle fibres are multinucleate
• Muscle fibres have long cylindrical orgonelles called microfibrils. They are made up of protein and are highly specalised for contraction.
• Skeletal muscles are made up of two types of muscle fibres - slow and fasttwitch. Different muscles have different proportions of slow and fast twitch fibres.

• Muscle fibres contract slowly

• Muscle fibres for posture contain a large proportion on slow muscle fibres.

• Good for endurance activities

• Can work for long periods of time without exhausting.

• Energyis releases through aerobic respiration.

• Contain lots of mitochondria and blood vessils to suply the muscles with oxygen.

• Reddish in colour because of richness of myoglobin (red, oxygen storing protein).

• Muscle fibers contract very quickly.

• Muscles used for fast movement. 

• Good for short bursts of speed and power.

• Tire easily.

• Energy is released quickly through anaerobic respiration using glycogen.

• Few mitochondria/blood vessels.

• White due to lack of myoglobin.

Sliding filament theory

• Myosin and actin filaments slide over one another to make scarcomeres contract - the myofiloments themselves don't contract.
• The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibers contract.
• Sarcomeres return to their original length when the muscle relaxes.

Myosin Filaments

• Myosin filaments have globular heads that are hinges so they can go back and forth.
• Each myosin head has a binding site fir actin and a binding site for ATP.
• Actin filaments have binding sites for myosin heads called actin-myosin binding sites.
• Two other proteins called tropomyosin and tropin are found between actin filaments. These proteins are attached to each other and they help myofilaments move past each other.

• In a resting (unstimulated) muscle the actin-myosin binding site is blocked by tropomyosin, which is held in place be troponin. This means that the myofilaments can't slide slide past each other because the myosin heads can't bind to the actin-myosin binding sites on the actin filaments.
• When an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolmma. Depolarisation spreads down the T-tubles to the sacroplasmic reticulum. This causes the sarcoplasmic reticulum to release stored calcium ions (Ca2+) into the sacrcoplasm, calcium ions bind to troponin, causing it to change shape. This pulls the attached tropomypsin out of the actin-myosin binding site on the actin filaments, exposing the binding site, which allows the mysoin head to bind. The bond formed when a myosin head binds to an actin filament is called the actin-myosin cross bridge.
• Calcium ions also activate the enzyme ATPase, which brakes down ATP (into ADP + Pi) to provide the energy needed for muscle contraction. The energy released from ATP moves the myosin head, which pulls the actin filament away.
• ATP also provides energy to break the actin-mysoin cross bridge, so the myosin head detaches from the actin filament after it has moved. The myosin then reattaches to a different binding site further along the actin filament. A new actin-myosin cross bridge is formed and the cycle is repeated during which many cross bridges form and break very rapidly, pulling the actin filaments along. This shortens the sacromere, causing the muscle to contract. This cycle will continue as long as Ca2+ ions are present and bond to troponin.

• When the muscle stops being stimulated, calcium ions leave their binding sites on the troponin molecules and are moved by active transport back into the sarcoplasmic reticulum (requires ATP).
• The tropin molecules return their original shape, pulling the attached tropomyosin molecules with them. This means the tropomyosin once again block the actin binding sites.
• Muscles aren't contracted because no myosin heads are attached to actin filamnets.
• The actin filaments slide back to their relaxed position, which lengthens the sacromere.

• Movement involves skeletal muscles, tendons, ligaments and joints.

• Skeletal muscles are the type of muscle you move.

• Skeletal muscles are attached to bones by tendons.

• Ligaments attach bones to other bones and hold them together.

• Skeletal muscles contract and relax to move bones at a joint.

• Muscles that work together to move a bone are called antagonistic pairs.

• The muscle that extends a joint is called an extensor and the muscle that flexes a joint when it contracts is called felxor.

• Muscles can only contract.

• The hip, knee and ankle joints are examples of synovial joints.

• These are where the bone articulate in the joint and are separated by a cavity filled with synovial fluid (allows for free movement).

• The bones are held in position by ligaments that control and restrict the amount of movement in the joint.

• Tendons attach muscles to bones, enabling muscles to  power joint movement.

• Cartilage protects the bones within the joints. 

• Aerobic respiration is the process where a large amount of energy is released by splitting glucose into CO2 (which is released as a waste product) and H2 (which combines with atmospheric CO2 to produce H2O)
• The energy is used to phosphorylate ADP to ATP. ATP is then used to provide energy for all the biological processes around the cell.
• There are four stages in aerobic respiration - glycolysis, the link reaction, the krebs cycle and oxidative phosphorylation.
• The first three stages are a series of reactions. The products from these reactions are used in the final stage to produce loads of ATP.
• Each reaction in respiration is controlled by a different enzyme.
• The first stage happens in the cytoplasm of the cell and the other three take place in the mitrochondria.
• Coenzymes are used in respiration. For example;
  • NAD and FAD trasnfer hydrogen from one molecule to another - this means they can reduce or oxidise a molecule.
  • Coenzyme A transfers acetate between molecules.
• All cells use glucose to respire, but organisms can also break down other complex organic molecules, which can then be respired.

• The volume of oxygen taken up or the volume of CO2 produced indicates the rate of respiration.
• A respiromiter measures the rate of oxygen being taken up - the more oxygen is taken up, the faster the respiration.
• Each tube contains potassium hydroxide solution (or soda lime), which absorbs carbon dioxide.
• The control tube is set up in exactly the same way as the test tube, but without the woodlice to make sure the results are only due to the woodlice respiring. (e.g. it contains beads that have the same mass as the woodlice).
• The syringe is used to set the fluid in the mamometer to a known level.
• The apparatus is left for a set period of time (e.g. 20 minutes).
• During that time there'll be a decrease in the volume of the air in the test tube, due to the oxygen consumed by the woodlice (all the CO2 produced is absorbed by the KOH).
• The decrease in the volume of air will reduce the pressure in the tube and cause the coloured liquid in the mamometer to move towards the test tube.
• The distance moved by the liquid in a given time is measured. This value can be used to calculate the volume of oxygen taken in by the woodlice per minute.
• Any variables that could affect the results are controlled, e.g. temperature, volume of KOH in each test tube.
• To produce more reliable results, experiment is repeated and mean volume of O2 calculated

• A cell can't getits energy directly from glucose.

• So, in respiration, the energy released from the glucose is used to make ATP (adenosine triphosphate). ATP is made from the neucleotide base adenine, combined with a ribose sugar and three phosphate groups.

• It carries energy around the cell to where it is needed.

• ATP is synthesised from ADP and inorganic phosphate (Pi) using energy from an energy releasing reaction, e.g. the break down of glucose in respiration. The energy is stored as chemical energy in the phosphate bond. The enzyme ATP synthase catalyses the reaction.

• ATP diffuses to the part of the cell that needs energy.

• Here it is broken down back into ADP and Pi. Chemical energy is released from the phosphate bond used by the cell. ATPase catalyses this reaction.

• The ADP and Pi are recycled and the process starts again.

Glycolysis makes pyruvate from glucose

• Glycolysis involves splitting one molecule of glucose (a hexose sugar, so has 6 carbons - 6C) into smaller molecules of pyruvate (3C)
• The process happens in the cytoplasm of the cells.
• Glyclysis is the first stage in both anaerobic and aerobic respiration and doesn't need oxygen to take place - so an anaerobic process.

Phosphorylation and oxidation

First ATP is used to phosphorylate glucose to triose phosphate. Then triose phosphate is oxydised, releasing ATP. Overall there in a net gain of 2ATP.

• Phosphorylation
  • Glucose is phosporylated by adding 2 phosphates from 2 molecules of ATP.
  • This creates 2 molecules of triose phosphate and 2 molecules of ADP.
• Oxydation
  • Triose phosphate is oxidised, forming 2 molecules of pyruvate
  • NAD collects the H+ ions, forming 2 reduced NAD.
  • 4ATP are produced, but 2 were used up in phosphorylation so there's a net gain of 2ATP.

The link reaction converts pyruvate to Acetyl-Coenzyme A (acetyl CoA)

• The link reaction takes place in the mitochondrial matrix.
• Pyruvate is decarboxylated - one carbon atom is removed from pyruvate in the form of CO2.
• NAD is reduced - it collects a hydrogen from pyruvate, changing pyruvate into acetate.
• Acetate is combined with coenzyme A (CoA) to form acetyl CoA.
• No ATP is produced in this reaction.

The link reaction happens twice for every glucose molecule.

• Two pyruvate molecules are made up for every glucose molecule that enters glycolysis. This means the link reaction and the third stage (krebs cycle) happen twice for every glucose molecule.
• For every glucose molecule;
  • Two molecules of acetyl CoA go to the krebs cycle
  • Two molecules of CO2 are released as a waste product of respiration.
  • Two molecules of reduced NAD are formed and go to oxidative phosphorylation.

The krebs cycle involves a series of oxidation - reduction reactions, which take place in the matrix of the mitochondria. Each of the reactions are controlled by a specific intercellular  enzyme. The cycle happens once for every pyruvate molecule, so goes round twice for every glucose molecule.

• Acetyl CoA from link reaction combines with oxaloacetate to form citrate.
• CoA goes back to link reaction to be used again.
• The 6C citrate molecule is converted to a 5C molecule.
• Decarboxylation occurs where CO2 is removed.
• The Hydrogen is used to produce reduced NAD from NAD.
• The 5C molecule is then converted to a 4C molecule.
• Decarboxylation and dehydogenation occur, producing 1 molecule rFAD & 2rNAD.
• ATP is produced by the direct transfer of a phosphate group from an immediate compound to ADP. When a phosphate group is directly transferred from one molecule to another its called substrate - level phosporylation. Citrate has now been converted into oxalacetate.

• 1CoA - reused in the next link reaction
• Oxalacate - regenerated for use in the next krebs cycle
• 2CO2 - released as waste product
• 1ATP - used for energy
• 3rNAD - to oxidative phosphorylation.
• 1rFAD - to oxidative phosphorylation.

• Oxidative phosphorylation is the process where the energy carried by electrons form reduced coenzymes (rNAD, rFAD), is used to make ATP.
• Oxidative phosphorylation involves processes - the electron transport chain and chemiosmosis.
• Hydrogen atoms are released from rNAD and rFAD as they're oxidised to NAD and FAD. The H atoms split into protons (H+), and electrons (e-).
• The electrons move along the electron transport chain (made up of 3 electron carriers), loosing energy at each carrier).
• The electron carrier is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space.
• The concentrations of protons is now higher in the intermembrane space than the mitochondrial matrix - this forms an electrochemical gradient.
• Protons move down the electrochemical gradient back down into the mitochondrial matrix, via ATPsynthase. This movement drives the synthesis of ATP from ADP and Pi.
• The movement of H+ ions across a membrane, which generates ATP, is called chemiosmosis.
• In the mitochondrial matrix, at the end of the transport chain, e-, H+ and O2 (from blood) combine to form H2O. O2 is said to be the final electron acceptor.

• Glycolysis
  • 7ATP (2 ATP + 2 x 2.5)
  • 2rNAD

• Link reaction (x2)
  • 2rNAD
  • 5ATP (2 x 2.5)

• Krebs cycle (x2)
  • 20 ATP (2 + 6 x 2.5 + 3 x 2.5)
  • 6rNAD
  • 2rFAD

Total ATP produced = 32ATP molecules per 1 molecule of glucose.

Lactate fermentation

• Anaerobic respiration doesn't use oxygen.
• It doesn't involve the link reaction, krebs cycle or oxidative phosphorylation.
• There are two two types of anaerobic respiration.
• Lactate fermentation occurs in animals and produces lactate
  • Glucose is converted to pyruvate via glycolysis
  • Reduced NAD (from glycolysis) transfers H to pyruvate to form lactate and NAD.
  • NAD can then be reused in glycolysis.
• The lactate production regenerates NAD. This means glycolysis can continue even when their isn't much O2 around, so a small amount of ATP can still be produced to keep some biological processes going.

Lactic acid needs to be broken down

• After a period of anaerobic respiration lactic acid builds up. Animals can break it down in two ways;
  • Cells can convert lactic acid back to pyruvate (when cells re-enter aerobic respiration at the krebs cycle).
  • Liver cells can convert the lactic acid back to glucose (Which can then be respired or stored)

Cardiac muscle controls the regular beating of the heart.

Cardiac muscle is 'myogenic' - it can contract and relax without receiving signals from neurons. This pattern of contractions controls the regular heart beat.

• The process starts in the sinoatrial node (SAN) which is in the wall of the right atrium.
• The SAN is like a pacemaker - it sets the rhythm of the heartbeat by sending out waves of electrical activity to the atrial walls.
• This causes the right and left atria to contract at the same time.
• A bind of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles.
• Instead, these waves of electrical activity are transferred by the SAN to the atrioventricular  node (AVN).
• The AVN is responsible for passing the waves of electrical activity into the bundle of His. But, there's a slight delay before the AVN reacts, ensuring the ventricles contract after the atria have emptied.
• The bundle of His is a group of muscle fibers responsible for conducting the electrical activity to the finer muscle fibers in the right and left ventricle walls, called pukyne fibres.
• Pukyne fibers carry the waves of electrical activity into the right and left ventricles, causing them to contract simultaneously, from the bottom up . 

An electrocardiograph records the electrical activity of the heart.

• Doctors check function of a heart using an electrocardiogram - machine that records electrical activity of the heart. The heart muscle depolarises when it contracts and repolarises when it relaxes. An electrocardiograph records change in electrical charge using electrodes placed on the chest. This places a trace called an electrocardiogram.
• The P wave is caused by contraction (depolarisation) of the atria.
• The main peak of the heartbeat, together with the dips either side is called the QRS complex - its caused by contraction of the ventricles.
• The T wave is due to the repolarisation (relaxation) of the ventricles.

Doctors use ECGs to diagnose heart problems.

• Doctors compare patients ECGs with normal trace. Helps diagnose any problems with the hearts rhythm, which may include CVD.
• Tachycardia - increased heart rate - heart beats too fast, could be sign of heart failure. A problem with the heart = can't pump blood efficiently, = heart rate increases to ensure enough blood is pumped around the body. Tachycardia can increase the risk of heart attack.
• Problem with the AVN - the impulses aren't travelling from the atria through to the ventricles.
• Fibrillation - irregular heartbeat. Atrial fibrillation = chest pains, fainting & increased risk of stroke. Ventricular fibrillation = death. It may caused by a heart attack.  

The medulla controls breathing rate

The medulla has areas called ventilation centers. There are two ventilation centers - the insiratory centre. They control the rate of breathing.

• The inspiratory centre in the medulla sends nerve impulses to the intercostal  and diaphragm muscles to make them contract. This increases the volume of the lungs, which lowers the pressure in the lungs. (The inspiratory centre also sends nerve impulses to the expiratory centre. These impulses inhibit the action of the expiratory centre.
• Air enters the lungs due to the pressure difference between the lungs and the air outside.
• As the lungs inflate, stretch receptors in the lungs are stimulated. The stretch receptors send nerve impulses back to the medulla. These impulses inhibit the action of the inspiratory center.
• The expiratory center (no longer inhibited) then sends nerve impulses to the diaphragm and intercostal muscles to relax. This causes the lungs to deflate, expelling air. As the lungs deflate, the stretch receptors become inactive. The respiratory centre is no longer inhibited and the cycle begins again

Heart rate is controlled by the cardiovascular control center in the medulla of the brain.

Decreased blood pH causes an increase in heart rate

• A decrease in blood pH (caused by an increase in CO2) is detected be chemoreceptors.
• The chemoreceptors send nerve impulse to the medulla.
• The medulla sends nerve impulses to the SAN to increase the heart rate.

Increased blood pressure causes a decrease in heart rate.

• Pressure receptors in the aorta wall and the carotid sinuses (at the start of the carotid arteries carrying blood to the brain) detect changes in blood pressure.
• If the pressure is too high, the pressure receptors send nerve impulses to the cardiovascular center, which sends nerve impulses to the SAN, to slow down the heart rate.
• If the pressure is too low, pressure receptors send nerve impulses to the cardiovascular centre, which sends nerve impulses to the SAN to speed up heart rate.

Breathing and heart rate increase when you exercise

When a person exercises their muscles contract more frequently, which means they use more energy. To replace this energy the body needs to do more aerobic respiration, so it needs to take in more oxygen and breath out more CO2. The body does this by;

• Increasing breathing rate and depth - to obtain more oxygen and to get rid of more Carbon Dioxide.
• Increasing heart rate - to deliver oxygen (and glucose) to muscles faster and remove out extra CO2, produced by the increased rate of respiration in muscle cells.

Ventilation rate increases with exercise

• Ventilation rate is the volume of air breathed in or out in a period of time.
• It increases during exercise because breathing rate and depth increase.

Exercise triggers an increase in breathing rate by decreasing blood pH

• During exercise, the level of CO2 in the blood increases. This decreases the pH of the blood.
• There are chemoreceptors in the medulla, aortic bodies (in the aorta) and carotid bodies (in arteries carrying blood to the brain) that are sensitive to changes in the blood.
• If the chemoreceptors detect a decrease in blood pH, they send nerve impulses to the medulla, which sends more frequent impulses to the intercostal muscles and diaphragm. This increases depth and rate of breathing.
• This causes gaseous exchange to speed up - the CO2 level drops and extra O2 is supplied to the muscles. 

Exercise triggers an increase in heart rate by decreasing blood pH

• During exercise, the level of CO2 in the blood increases. This decreases the pH of the blood, which chemoreceptors detect. This leads to an increase in heart rate

Cardiac output increases with exercise

• Cardiac output is the total volume of blood pumped by the ventricle every minute.
• The equation for working out cardiac output is:

Cardiac output (Cm3/min) = heart rate (bpm) x stroke volume (Cm3)

• So cardiac output increases during exercise because heart rate increases (stroke volume also increases because the heart pumps harder as well).

Stroke volume is the volume of blood pumped by one ventricle each time it contracts

Tidal volume is the volume of air in a normal breath

• Tidal volume - the volume of air in each breath, usually about 0.4 dm3
• Breathing rate - how many breathes are taken, usually in a minute
• Ventilation rate - the volume of air breathed in or out, usually in a minute

Ventilation rate = tidal volume x breathing rate

Spirometers can be used to investigate the effects of exercise

• Exercise causes an increase in breathing rate and tidal volume. A spirometer can be used to measure the change in breathing rate and tidal volume at rest, during exercise and after exercise. For example;
  • A person is connected to a spirometer using a mask so that continuous readings can be recorded.
  • Readings are recorded for one minute at rest.
  • The person then begins to exercise, e.g. running on a treadmill for 2 minutes.
  • The person stops exercising and readings are continued for 1 minute at rest

Spirometers can be used to measure tidal volume and breathing rate

• A spirometer is a machine that give readings of tidal volume and breathing rate.
  • A spirometer has an oxygen-filled chamber with a movable lid.
  • A person breathes through a tube connected to the oxygen chamber.
  • As the person breaths in the lid of the chamber moves down. When they breath out it moves up.
  • These movements are recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace.
  • The soda lime in the tube absorbs carbon dioxide as the person breaths.
• The tidal volume of gas in the chamber decreases over time. This is because the air that's breathed out is a mixture of oxygen and carbon dioxide. The carbon dioxide is absorbed by the soda lime - so there's only oxygen in the chamber which the person inhales from. As this oxygen gets used up by respiration, the total volume decreases.

Homeostatic system detect a change and respond by negative feedback

• Homeostatic system involve receptors, a communication systems and effectors
• Receptors detect when a level is too high or too low, and the information's communicated via the nervous system or the hormonal system to the effectors.
• The effectors respond to counteract the change - bringing the level back to normal.
• The mechanism that restores the level to normal is called a negative feedback mechanism.
• Negative feedback keeps things around the normal level
• Negative feedback only works within certain limits though - if the change is too big then the effectors may not be able to counteract to change it.

Mammals have many feedback mechanisms to change body temperature

To reduce body temperature;

• Sweating - more sweat is secreted from sweat glands when the body is too hot. The water is sweat in sweat evaporates from the surface of the skin and takes heat from the body. The skin is cooled.
• Hairs lie flat - mammals have a layer of hair that provides insulation by trapping air. When its hot, erector pili muscles relax so the hairs lie flat. Less air is trapped, so the skin is less insulated and heat can be lost more easily.
• Vasodilation - when it's hot, arterioles near the surface of the skin dilate. More blood flows through the capillaries in the surface layers of the dermis. This means more heat is lost from the skin by radiation and the temperature is lowered.

To increase body temperature;

• Shivering - when it's cold, muscles contract in spasms. This makes the body shiver and more heat is produced from increased respiration.
• Hormones released - the body releases adrenaline and thyroxine, which increase the metabolism so more heat is produced
• Much less sweat - is secreted from sweat glands when its cold, reducing the amount of heat loss.
• Hairs stand up - erector pili muscles contract when it's cold, which makes the hairs stank up. This traps more air, and prevents heat loss.
• Vasoconstriction - when its cold, arterioles near the surface of the skin contract so less blood flows through the capillaries in the surface layers of the dermis. This reduces heat loss.

Homeostasis is the maintenance of a constant temperature

• Your external environment and what you're doing (e.g. exercising) can you can affect you internal environment - the blood and tissue that surrounds your cells (e.g. exercise increases body temperature)

• Homeostasis involves control systems that keep your internal environment roughly constant - your internal environmental is kept in a state of equilibrium.

• Keeping your internal environment at a constant temperature is vital for your cells to function normally and to stop them being damaged. For example, if body temperature becomes too high (e.g. 40C), enzymes may become denatured. The enzyme molecules vibrate to much, which breaks the hydrogen bonds that hold them in their 3D shape. The shape of the enzymes active site is changed and it no longer works as a catalyst. This means metabolic reactions are less efficient.

The hypothalamus controls body temperature in mammals

• Body temperature in mammals is maintained at a constant level by a part of the brain called the hypothalamus.

• The hypothalamus receives information about temperature from thermoreceptors.

• The thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors.

• The effectors respond to restore the body temperature back to normal

• The control of body temperature is called thermoregulation

Hormones switch genes on to regulate temperature

• In a cell there are proteins called transcription factors that control the transcription of genes.
• Transcription factors bind to DNA sites near the start of genes and increase or decrease the rate of transcription. Factors that increase the rate are called activators and those that decrease the rate are called receptors.
• Hormones can bind to some transcription factors to change body temperature;
  • At normal body temperature, the thyroid receptor (a transcription factor) binds to DNA at the start of a gene.
  • This decreases the transcription of a gene coding for a protein that increases metabolic rate.
  • At cold temperatures, the thyroxine is released, which binds to the thyroid hormone receptor, causing it to act as an activator.
  • The transcription rate increases, producing more protein. The protein increases the metabolic rate, causing an increase in body temperature.

Physical activity has many advantages. These include;

• Increasing arterial vasodilation lowers blood pressure; this reduces the risk of coronary heart disease and stroke.
• Physical activity increases the levels of blood HDLs, which transport cholesterol to the liver where it is broken down, and reduces LDLs, which are associated with development of atherosclerosis, coronary heart disease and stroke.
• A balance of energy input and output helps maintain a healthy weight.
• Increased sensitivity of muscle cells to insulin producing cells to insulin improves blood glucose regulation, and reduces the likelihood of developing type II diabetes.
• Physical activity increases bone density and reduces its loss during old age; this delays the onset and shows the progress of the bone-wasting disease osteoporosis.
• Exercise reduces the risk of some cancers.
• It improves mental well being.

Not doing enough exercise can be unhealthy

Taking to little exercise means that many of the heath benefits associated with exercise are not achieved. Many studies have looked at the effects of doing too little exercise, the results have found that not enough exercise can lead to: 

• Increased risk of obesity (linked also to overeating and drinking)
  • Leads to high blood pressure and high LDL levels, which increases the risk of CHD and stroke
• Higher risk of coronary heart disease
• Higher risk of stroke 
• Higher risk of Cancer
• Higher risk of Diabetes and...
•  ...Higher risk of osteoporosis.

Doing too much exercise can be unhealthy too.

• Athletes engaged in heavy training programs seem to be more prone to infection than normal. This has been suggested to be due to; increased exposure to pathogens and suppressed immunity with hard exercise.
• Moderate exercise increases the number of activity of natural killer cells, which provide non-specific immunity against cells invaded by viruses and cancerous cells.
• Research shows that, during recovery after vigorous exercise, the number and activity of natural killer cells, phagocytes, B cells and T-helper cells falls. This depresses the specific immune response.
• Both psychological stress (due to heavy training schedules) and physical stress cause secretion of adrenaline and cortisol which are known to suppress the immune system.
• Heavy physical activity can also lead to were and tear of the joints. This damage can include wear of cartilage (which can lead to a form of arthritis), swelling of knees and other sinovial joints due to a build up of fluid and damaged ligaments. 

Some injuries can cause permanent damage to the body, e.g. head or spinal injuries. But people can recover form some injuries if treated correctly. A lot of injuries happen when playing sports because the body's put under a lot of stress. Advances in medical technology can help people with an injury to recover and participate in sports. One advancement is keyhole sugary;

• Keyhole sugary is a way of doing sugary without making a large incision in the skin.
• Surgeons make a much smaller incision in the patient, and they insert a tiny video camera and specialised medical instruments through the incision into the body.
• There are many advantages of keyhole sugary over regular sugary;
  • Operations don't involve opening up the patient as much, so patients lose less blood and have less scaring of the skin.
  • Patients are usually in less pain after their operation and they recover more quickly, because less damage is done to the body.
  • This makes it easier for the patient to return to normal activities and their stay in hospital is shorter.

Injuries aren't usually fixed by sugary alone - other treatments are needed too for a full recovery.

Prostheses can replace damaged body parts

Some people are born without a particular body part, others suffer injuries that result in them losing or badly damaging a body part. Sometimes it is possible to replace damaged or missing body parts with an artificial device called a prostheses;

• Prostheses can be used to replace whole limbs or limb parts.
• Some prostheses include electronic devices that operate the prosthesis by picking up information sent by the nervous system.
• So prostheses make it possible for people with some disabilities to participate in sport.
• They also make it possible for people who have certain injuries to play sport again.

Some athletes use performance-enhancing drugs

When involved in very competitive sport, some people choose to take performance-enhancing drugs - these are drugs that will improve a persons performance. There are various kinds of performance enhancing drugs that have different effects on the body, for example;

• Anabolic steroids - these drugs increase strength, speed and stamina by increasing muscle size and allowing athletes to train harder. They also increase aggression.
• Stimulants - these drugs speed up reactions, reduce fatigue and increase aggression.
• Narcotic analgesics - these drugs reduce pain, so injuries don't affect performance.

Performance-enhancing drugs are banned in most sports. Athletes can be tested for drugs at any time and if they're caught, they can be banned from competing and stripped of any medals.

There are many arguments why performance-enhancing drugs are banned but some people think they should be allowed in sport.

Against

• Some performance-enhancing drugs are illegal
• Competitions become unfair if some people take drugs - people gain an advantage by taking drugs, not through training or hard work.
• There are serious health risks associated with the drugs used, such as high blood pressure and heart problems.
• Athletes may not be fully informed of the health risks of the drugs they take.

For

• It's up to each individual - athletes have the right to make their own decision about taking drugs and whether they are worth the risk or not.
• Drug-free sport isn't really fair anyway - different athletes have access to different training facilities, coaches, equipment, etc. 
• Athletes that want to compete at a higher level may only be able to by using performance-enhancing drugs