The Physiology of Fitness

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17 March 2016

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What is an acute response?
An acute response is an immediate response to exercise.
Acute exercise will last throughout the full length of your training session. During the training session our bodies begin to respond to the exercises we are doing and begin to feel the changes within our bodies and mind due to physical strain and stress of the physical activity in lots of different ways.

Musculoskeletal response

Increased blood supply: the increased blood supply occurs in the body due to the increase in demand for more oxygen and this is due to the working muscles needing more oxygen and energy during exercise. With there been an increase in blood supply that means there will be greater amounts of oxygen been delivered around the body at a faster speed due to the heart pumping blood around the body at a faster pace. Increase in muscle pliability: Muscle pliability is the stretchiness of your muscles and connective tissues. When muscles become warm they become more pliable and this helps reduce the risk of an individual becoming injured during exercise and this is because the muscles contract quickly when the body is exercising. When the muscles are contracting they produce heat which then a=makes the muscle more pliable.

The warmer the muscle becomes the further you can stretch it each time without the muscle becoming weakened or injured. Increased range of movement: Synovial fluid is the result of joint movement and allows joints to move without them rubbing together and causing friction. During exercise joint changes occur and this is because the synovial fluid becomes less viscous (the measure of thickness of a fluid) so therefore the range of movement at the joint will increase. Muscle fibre micro tears: When muscles are put under pressure whilst exercising tiny tears occur. These tears within the muscles cause swelling, which then puts pressure on the nerve endings which causes a lot of pain. To help strengthen the muscles and help repair the micro tears you need to rest and you can strengthen the muscles by training.

Energy systems

Everything in our bodies requires energy and our body mainly needs energy to move. Energy can be generated in different ways and this is depending upon the duration or intensity of the exercise that the individual is performing. Phosphocreatine: The ATP-PC system can also been known as the alactic acid system. During exercise the ATP-PC energy system works between 1-10 seconds long it usually consists of different sport activities like: high jumpers, long jumpers, javelin and shot putters. This energy system doesn’t produce lactic acid and it works without oxygen. When the body has been doing exercise your body uses the energy source ATP. When ATP has been used within the body this energy system is the first fuel to be called upon the body to resynthesize ATP. ATP-PC utilizes Phosphatecreatine and this then allows high intensity muscle contractions. The maximum storage this energy can take up without the individual training is less than 8 seconds in duration. So this means that this energy system can work at a high intensity but only for a short period of time! There are ways in which Creatine phosphate (CP) can be increased within the human body and that is through training. By training levels of CP will increase by:

•Speed training
•Creatine loading

Both of these delay the use of the lactic anaerobic system but even though it delays it still gives 15 seconds of energy stored in the body. The ATP is stored in the muscle and liver and this can produce energy quickly. Nerve impulses in the body trigger the breakdown of ATP into ADP, however for this to continue ad for the body to continue to use this energy system, the ATP must be resyntesized /rebuilt and this comes from the splitting of phosphocreatine. When the ATP is used, it is rebuilt but this will only happen as long as there is phosphocreatine available within the body. Energy is released from the phosphocreatine breaking off and from this it resynthesizes in the mitochondria and the ADP adds on the phosphate to remake ATP.

The ATP-P system doesn’t provide a lot of energy but it is used for quick and powerful movements. For example: A 100m runner would use the ATP-PC system due to the fact that the athlete would need a short powerful burst of movement to be able to get off the blocks quickly. Another example of this energy is for a shot putter. They would use this energy system because they don’t need a lot of energy for their sport, all they need is a short powerful burst of energy to be able to get a strong, powerful thrown and to be able to throw the shot-putt a long way. All these different sporting examples last up to 8-10 seconds and this is the energy production. The speed of energy production for Phosphocreatine is very fast, although the amount of ATP produced is very limited.

The time it takes to recover from the ATP-PC energy system is 30 seconds up to 4 minutes. The phosphocreatine works when your body is working at high intensity at around 90-100%. The strengths of the Phosphocreatine system is because the source is stored in the muscles and liver so it can produce energy very quickly using a short burst. This means that there will be a higher force of contraction. There are also no waste products within this system. Another advantage/strength of this energy system is the recovery time. Phosphocreatine recovery time is shorter than the others which mean that the athlete can perform the event again quickly. For example: shot putters use this energy system because they have to perform 3 throws within a short period of time, so because the recovery time is between 30 seconds to 3 minutes this is the perfect energy system due to the fact they need to recover quickly to be back to their top level of performance.

To improve the force of contraction, an athlete should do plyometric training and Creatine loading, this will increase powerful movements. There are some weaknesses of the Phosphocreatine system and there are: the amount of ATP that is produced is limited. It is limited due to the Creatine been stored in the muscles and liver. Although it gives a short burst of energy it only lasts around 8 seconds which is a weakness if it is used for endurance events because it wouldn’t be able to produce an explosive and powerful movement. A marathon runner wouldn’t be able to use this Phosphocreatine system because it only releases a short burst of energy of about 8 seconds whereas marathon runners need to use the aerobic energy system because the duration is unlimited and the oxygen will never run out.

Lactic acid: This energy system is used without using any oxygen. It is used for activities that use large amounts of energy over a short period of time. The glycogen stored in the muscles helps the breakdown of ATP to become ADP with no oxygen involved. Seen as though the glycogen is stored in the muscles and liver it is available quickly. This system provides ATP when ATP-PC runs out. ATP-PC lasts for a few seconds; the lactic acid system is an anaerobic energy system which allows 2-3 minutes of work. In the lactic acid system the process to produce ATP is not as fast as ATP-PC which makes contractions slower. When oxygen is not present the end product of glycolysis is lactic acid this causes the muscles to fatigue.

Anaerobic glycolysis but it is then less efficient in producing ATP than aerobic glycolysis but is needed for a large burst of energy lasting a few minutes. The speed of the energy production in the Lactic acid system is fast, the energy source is glycogen. Although the amount of ATP produced is limited. Lactic acid is the by product in the production of waste products. This anaerobic energy system is used when the body is working at a moderate intensity of 60-95%. The length of time it takes to recover when the Lactic acid system has been used is 20 minutes up to 2 hours. For example: This energy system would be used for events and sports such as 800m, football and rugby games. The Lactic acid energy system would be used when an athlete is performing the 800m because you need a large burst of energy but you need it to last for a few minutes, as you do for a football, rugby game.

Although all these sports would use all of the energy systems in some form. You would also use this anaerobic energy system for football/rugby game because the glycogen is stored in the muscle and liver so it is available quickly and the time is takes to recover is short so it can keep replenishing itself throughout the game. The strengths of the Lactic acid system is that is produces energy quickly, compared to the aerobic system because that releases energy slowly but lasts for an unlimited duration whereas the lactic acid system is a high intensity but for a long duration. This system lasts longer than the Phosphocreatine system because the lactic acid system uses glycogen stores which aid the resynthesis of ATP. The weaknesses of this system are that it doesn’t last as long as the aerobic energy system because the glycogen stores are limited which means it doesn’t produce energy for as long. Another disadvantage is that it causes lactic acid within the muscles which causes muscle soreness and fatigue which could lead to a drop in intensity.

Aerobic: The aerobic energy system is the energy system that uses oxygen; it uses large muscle groups continuously over a period of time. Aerobic glycolysis and fatty oxidation is the resynthesis of ATP from carbohydrates and fat. Aerobic glycolysis uses glucose from the stores of the body. Glucose and oxygen are transported by the working muscles by the blood. These substances are then used by the body to produce energy. These substances are then used by the body to produce energy. This process creates the by-products carbon dioxide and water. This energy system is used for intensity exercise because this system uses oxygen. This allows unlimited duration at low intensity. Aerobic energy system uses long chain stores of glucose, this then break up further into glucose which is then used as a fuel within the body. This happens through the process of glycolysis and then in to the Krebs cycle where here it completes the oxidation of glucose, this creates more ATP.

The chemical process in which it goes through, an aerobic glycolysis occurs is when Creatine Phosphate runs out, the muscles call upon the stores of glucose (glycogen). This system creates a waste product which is called Pyruvic acid. The body deals with this by the oxygen breaking down the Pyruvic acid into carbon dioxide and water. However if activity levels are too intense and not enough oxygen can be inspired then the Pyruvic acid is not broken down and it then converts into lactic acid. The speed of energy production for the aerobic energy system is slow but the amount of ATP that is produced is unlimited. This is why this energy system is used for marathon runners and cross country runners because they need to use large muscle groups within their body but for a long period of time.

They also use this system because the amount of oxygen produced is unlimited so they can produce energy forever and ever without the oxygen never running out. This is why the lactic acid system and Phosphocreatine system isn’t used for long distance runners because the oxygen will run out. The advantages of the anaerobic energy system are that the system will work for an unlimited period providing glycogen stores and oxygen with high enough levels. This system lasts longer than the other two which allows an athlete to maintain high workloads for longer period of time. Another advantage would be that it can respond to high workloads much more quickly than the aerobic system meaning it can last for longer periods of time.

Furthermore the anaerobic energy system is capable of supplying fuel to the cells even when there is an oxygen deficit, which means that even when there is low oxygen the cells will still get some energy. The disadvantages of the anaerobic system are the fact that due to the lack of oxygen, glycolysis takes place which is catabolic (destructive) to the muscle cells if the process continues for too long. Lactate and hydrogen ions are produced. The lactate is used to continue energy production (current theory), while the hydrogen ions irritate the muscle tissue and chemically limit muscle contraction.

This creates the burning sensation and the heavy wooden feeling in the muscles. Another disadvantage to this energy system would be that the system cannot supply energy for extended periods. When fully trained, an athlete can sustain sub anaerobic threshold intensities for 1 to 1.5 hours. Fuel resources are used up very rapidly and the body cannot synthesize fats and protein quickly enough to supply this system so, glycogen and carbohydrates must be used.

Energy continuum: The term energy continuum is used to describe the types of energy system that are used during various physical activities. Energy is obtained through food and this is particularly carbohydrates and fats. This energy is transferred from the food into the proteins that are in the muscles. By the body doing this it will help determine the capacity at which intensity the body will exercise for. •The energy continuum is the interaction of the 3 energy systems to provide energy to resynthesize ATP.

It shows the predominant system or percentage of each system dependant on their intensity and duration of the activity. •The most dominant energy system within our bodies would be the ATP/PC. At the beginning of exercise all three energy systems start however as we begin to exercise the PC (Phosphate Creatine) is used up meaning the lactic acid system then takes over. After this (depending on the intensity of the activity), the lactic acid/aerobic energy system is reached between 1-3 minutes. The aerobic system now becomes the main provider of energy for the ATP resynthesis.

Describe the cardiovascular and respiratory systems responses to acute exercise Heart rate anticipatory response: This means the rate that the heart reaches before the start of exercise. When the body knows that it’s about to do exercise, the heart rate increases even though no exercise has been done yet. Nerves release chemicals in the body which adjust the heart rate to increase the heart rate. This is because the body knows exercise is about to be done therefore the heart rate increases pumping more oxygenated blood to the muscles ensuring that the muscles already have a sufficient supply of oxygen for when they begin to exercise. Activity response: The activity response is very similar to the heart rate anticipatory response. At the start of exercise, nerves in the medulla detect cardiovascular activity.

The nerves then send out chemical signals which increase the heart rate and the strength at which the heart is pumping. This makes more blood travel to the working muscles faster which is vital as the blood contains oxygen which ensures the muscles can carry on working. Regional blood flow is also altered to meet the requirements of blood needed at working places. This means that the working areas such as the quadriceps when running will have a higher blood flow coming to it than un-working areas such as the kidneys. Increased blood pressure: There are two types of blood pressure and these are known as systolic and diastolic.

One of the body’s acute responses to exercise is to increase the blood pressure. This is because the demand for oxygenated blood to the working muscles increases therefore the amount and speed of the blood going to the working muscles must also increase. There are mechanisms in place which prevent blood pressure getting too high as this can cause a heart attack and possible death.

Vasoconstriction: Vasoconstriction is when the body notices a change in temperature and begins become to come cold and it does certain things to ensure the body doesn’t lose too much heat. The blood vessels of the body constrict which means they decrease in size and this ensures as much heat as possible remains in the body as there is a smaller surface area and the blood flow decreases. Vasodilatation: Vasodilatation is one of the mechanisms the body has in place to ensure it remains at a safe temperature. It is the opposite of vasoconstriction in the way that vasodilatation functions to cool the body down. When the body notices the temperature is too high, the blood vessels will dilate which means to increase in size in an attempt to increase the blood flow. The larger surface area allows more heat to diffuse out of the body and therefore cools the body down.

Control of breathing (neural): When an individual is doing exercise their body needs more oxygen to be brought into our to the fact the demand for oxygen increases from the working muscles in order to carry on working. This is why our breathing rate increases when we are doing exercise. More oxygen is brought in by the increased breathing rate which goes on to be diffused into the blood and transported to the working muscles. If breathing rate didn’t increase, there wouldn’t be enough oxygen to meet the demands of the working muscles and exercise wouldn’t be able to take place. Control of breathing (chemical): Within our bodies there are things called chemoreceptors and these are what help to detect an imbalance of carbon dioxide levels and oxygen levels in the blood.

Chemoreceptors are hydrogen ions that measure the pH levels of the blood. If something is not right, this hydrogen ion can tell the breathing rate to increase to ensure that the blood becomes neutral again. Increased tidal volume: Tidal volume is the measure of the amount of air inhaled and exhaled with each breath we take. During exercise, the tidal volume increases a significant amount. This increase happens as the breathing rate has to meet the huge demands of oxygen needed by the respiring muscles. The increase of the tidal volume allows a bigger intake of oxygen and also a bigger exhale of carbon dioxide which is produced by the working muscles and needs to be out of the body as it is a waste product.

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"The Physiology of Fitness" StudyScroll, Mar 17, 2016.

"The Physiology of Fitness" StudyScroll, 17-Mar-2016. [Online]. Available: [Accessed: 25-Jun-2022]

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