Week 7 - Exercise Physiology

What is ATP? Describe the bonds attaching the last two phosphate radicals. What happens when a single phosphate radical is removed? How long can the energy present in muscles sustain maximal power for? What does this mean is required?

Adenosine triphosphate (ATP) is the energy driver within the body. The bonds attaching the last two phosphate radicals to the ATP molecule are really high-energy phosphate bonds, each of which stores around 7,300 calories of energy per mol of ATP under standard conditions. When a single phosphate radical is removed from the ATP, more than 7,300 calories of energy are released and energies the muscle contractile process. ATP then becomes ADP. When the second phosphate radical is removed, another 7,300 calories of energy are released, and the ADP becomes AMP. However, the energy present in the muscles, even in elite athletes, can only sustain maximal power for ~3 seconds, which is probably enough for a 50m sprint. Therefore, for events longer than 3 seconds, it is important that ATP is constantly formed.

Describe the relationship between work output, cardiac output and oxygen consumption. Contrast the increase in cardiac output in an untrained and trained individual. How does the heart-pumping effectiveness differ as well?

All these factors are directly related to one another through a linear relationship. Muscle work output increases oxygen consumption and increased oxygen consumption then in turn dilates the blood vessels in the muscles, therefore increasing venous return and increasing cardiac output. The typical cardiac outputs at several levels of exercise are shown in the table above. Remember that cardiac output has a time element to it. Therefore, the normal, untrained person can increase cardiac output over 4 fold. The well-trained athlete can increase output over 6 fold during exercise. The heart pumping effectiveness of each heartbeat is 40-50% greater in the athlete than the untrained person. There is also a corresponding decrease in the heart rate at rest for an athlete lower than an untrained individual.

Is an enlarged heart a bad thing?

An enlarged heart is a bad thing for a normal person and is a serious medical problem. The difference between the enlarged hearts of marathon runners and people with a medical problem is that if marathon runners stop training, their heart should return to a normal size. For people with a medical issue, their heart will remain enlarged, which indicates that heart enlargement is not due to maximal exercise.

Describe the effect of diet on muscle mechanical work. What measure of muscle performance does diet determine? What does a high-carbohydrate diet provide? How does this affect the muscles?

Another measure of muscle performance is endurance. More than anything else, endurance depends on diet, and the amount of glycogen which has been stored in the muscles. A high-carbohydrate diet is able to provide high levels of glycogen, which increases the time over which muscles can perform. Not only does a high-carbohydrate provide higher levels of glycogen in the diet, but it also enables endurance to improve.

Describe the relationship between muscle blood flow and exercise.

Blood flow increase is as important as blood flow decrease. 1. Contractile processes temporarily decrease muscle blood flow due to compression of intramuscular blood vessels. This is because the contracting skeletal muscle actually compresses on the intramuscular blood vessels. Therefore, a large decrease in muscle blood flow is observed. 2. Blood flow to muscles increases markedly during exercise. This is why the sympathetic nervous system kicks in.

Describe the relationship between stroke volume and cardiac output.

Cardiac output increases from 5.5L/min to 30L/min. Stroke volume increases from 105 to 162mL. Heart rate increases from 50 to 185 beats/min. As cardiac output increases, the approximate changes in heart rate and stroke volume from resting to marathon runners also increases. Stroke volume increases around 50%, whereas heart rate increases around 200%. Therefore, the heart rate accounts for a far greater proportion for the increase in cardiac output than the stroke volume does in strenuous cardiac exercise. As stroke volume reaches a maximum, any further increase in cardiac output observed after this has to be due to an increase in heart rate.

Describe the cardiac system as the limiting factor.

Cardiac output is about 90% the maximum a person can achieve during exercise, whereas the pulmonary system is only about 65%. During maximal exercise, both the stroke volume and heart rate are increased to about 95% of their normal levels. As cardiac output is = stroke volume X heart rate, cardiac output is about 90% the maximum that the person can achieve during exercise. Oxygen utilization by the body can never be more than the rate at which the cardiovascular system can transport oxygen to the tissues. The cardiovascular system is much more a limiting factor than the respiratory system in regard to the maximum we can achieve. Therefore, an athletes performance depends on the capability of the athlete's heart.

Describe the changes to muscles undergoing hypertrophy. How does muscle hypertrophy affect the anaerobic and aerobic systems?

Changes to muscles undergoing hypertrophy are as follows: 1. Increased number of myofibrils. 2. Up to 120% increase in mitochondrial enzymes. 3. 60-80% increase in components of phosphagen metabolic system. 4. 50% increase in stored glycogen. 5. 75-100% increase in stored triglyceride. Because of all these changes, the capabilities of the anaerobic and aerobic systems are increased if you undergo a training program which induces muscle hypertrophy.

What is endurance dependent on?

Endurance is also dependent on diet. Most energy is derived from carbohydrates in the first seconds and minutes of exercise, whereas towards exhaustion fat is used.

How can glycogen be used for energy? Does this process require oxygen? How is ATP formed this way? How does pyruvic acid from ATP? What happens when oxygen is absent? Where does lactic acid go? How fast can ATP be formed this way (glycogen-lactic acid system) compared to oxidative metabolism and the phosphagen system? How long can activity be sustained in this way?

Glycogen in our muscles can be split into glucose, which can then be used for energy. The initial stage of this process is known as glycolysis and occurs without the use of oxygen (known as an anaerobic process). The glucose molecule is then split into two pyruvic acid molecules which leads to energy released to form four ATP molecules for each glucose molecule. Normally the pyruvic acid then enters the mitochondria cells to react with oxygen to form more ATP molecules. However, if there is insufficient oxygen, then most of the pyruvic acid is actually converted into lactic acid. Lactic acid diffuses out of the muscle cells into the interstitial fluid. It is a by-product of anaerobic metabolism. Therefore, a lot of the muscle glycogen is actually transformed into lactic acid. However, in doing so, a lot of ATP is formed entirely without the consumption of oxygen (anaerobic). A key characteristic of this system is that it can form ATP 2.5 times faster than oxidative metabolism, however only half as fast as the phosphagen system. Under optimal conditions, the glycogen-lactic acid system provides 1.3 to 1.6 minutes of maximal muscle activity, although with a somewhat reduced power compared to the phosphagen system.

Describe muscle hypertrophy. What are big factors of muscle hypertrophy? How much can muscle be hypertrophied? Does muscle hypertrophy increase diameter or fibre number?

Hereditary and testosterone levels are big factors of muscle hypertrophy. Muscle can be hypertrophied an additional 30-60%. This comes from an increased diameter rather than increased numbers of fibres.

How much energy is provided by breaking the phosphate bond?

If you break the phosphocreatine bond, you can get 10,300 calories per mole. Therefore, phosphocreatine can provide enough energy to reconstitute this high-energy bond of ATP.

Describe the differences in male and female exercise values. Where does most of the difference lie? What hormone plays a large role?

In general, most quantitative values for women vary between 2/3 to ¾ of the values recorded in men. This includes measurements related to muscle mass such as muscle strength, pulmonary ventilation and cardiac output. However, there are many exceptions to this generalization. Most of the difference lies in the extra percentage of muscle that males tend to have. However, female muscle can achieve the same force in terms of strength per square centimetre. Male athletes tend to have a greater amount of muscle, not stronger muscle. Testosterone also plays a large role due to its powerful anabolic effect.

Describe heart hypertrophy.

Marathoners and endurance athletes can achieve maximal cardiac outputs that are ~40% greater than untrained persons. Heart hypertrophy refers to heart muscle growth. Heart mass and heart chambers enlarge by ~40%. Increase in heart-pumping effectiveness is the key. From the data, it is clear that marathoners can achieve maximal cardiac outputs that are about 40% greater than that of untrained persons. This results mainly from the fact that the heart chambers of marathoners can enlarge by about 40%. Along with this, the heart mass also increases by about 40% or more. Not only do skeletal muscles undergo hypertrophy during athletic training, but so does the heart. However heart enlargement and increased pumping capacity occurs almost entirely in endurance athletes, not sprint athletes. However, resting cardiac output remains very similar for both athletes and non-athletes. This is because although the stroke volume is increased in athletes, the heart rate is reduced (during resting). The important thing is that the heart-pumping effectiveness is increased in the marathoner.

What is the value of maximal breathing capacity? When does it provide extra ventilation? How does maximal breathing capacity provide an element of safety?

Maximal breathing capacity is about 50% greater than the pulmonary ventilation during maximal exercise. Maximal breathing capacity provides extra ventilation during: - High altitudes. - Exercise under high temperatures. - Abnormalities in the respiratory system. As maximal breathing capacity is about 50% greater than pulmonary ventilation, this provides an element of safety for athletes, as there is extra ventilation which they can call upon, for example in high altitudes.

What is muscle mechanical work? How is the power of the muscle determined? What is the power a measure of?

Muscle mechanical work is the amount of force applied by the muscle x the distance over which that force is applied. The power of muscle is determined by the strength and also the distance of contraction and the number of times it contracts per minute. The power of muscle is measured in kilogram metres per minute (kg-m/min). The power is a measure of the total amount of work that a muscle performs in a unit period of time. Different systems begin to kick in to sustain muscle power as time elapses.

Does strength increase when muscles function under no load? When do muscles develop rapidly? What is an increase in muscle mass called? Describe the graph of the increase in muscle strength.

Muscles which function under no load increase little in strength. Conversely, muscles that contract at more than 50 percent maximal force of contraction will develop rapidly. An increase in muscle mass is known as hypertrophy. Muscle strength increases in the first 4-6 weeks, and then plateaus after that time.

What is the value of normal oxygen consumption? How much does this value increase between resting and maximal intensity? How important is respiratory ability in sprint athletics compared to endurance exercises?

Normal oxygen consumption for a young male is approximately 250ml/min, however this number can increase about 20 fold between resting and maximal intensity. One's respiratory ability is actually of very little importance in sprint types of athletics, but it is critical for endurance and maximum performance type exercises.

What is the oxygen diffusing capacity? How is it measured?

Oxygen-diffusing capacity is the rate at which oxygen can diffuse from the pulmonary alveoli into the blood. Oxygen-diffusing capacity is measured in millilitres of oxygen that will diffuse each minute for each millimetre of mercury difference between the partial pressure of oxygen in the alveoli and pulmonary capillaries. The amount of oxygen which diffuses through the respiratory membrane each minute is equal to the oxygen-diffusing capacity.

What does phosphocreatine decompose to? What does this release? What is the energy transfer from phosphocreatine to ATP referred to as? How does the energy released by phosphocreatine compare to ATP?

Phosphocreatine decomposes to creatine and phosphate, releasing large amounts of energy. Muscle cells have 2-4 times as much phosphocreatine as ATP. Phosphocreatine also has a high-energy phosphate. A special characteristic of phosphocreatine is that the energy transfer to ATP occurs within a small fraction of a second, and therefore is regarded as an instantaneous energy source. The breaking of the phosphocreatine bond actually releases more energy than that of ATP.

Describe muscle recovery and how the glycogen-lactic acid system can be used to reconstitute both phosphocreatine and ATP.

The Glycogen-lactic acid system can be used to reconstitute both phosphocreatine and ATP. The removal of lactic acid is important as excess lactic acid can cause extreme fatigue. 1. A small portion of lactic acid is converted back into pyruvic acid and metabolized oxidatively. 2. Lactic acid is also reconverted into glucose mainly in the liver. Glucose then replenishes glycogen storage in muscles.

What is the aerobic system? What is AMP converted into? What is combined in this process? What does the restoration of the aerobic system depend on?

The aerobic system is the oxidation of foodstuffs in the mitochondria to provide energy. This involves the conversion of AMP and ADP into ATP, so that the bonds of ATP can be broken again to provide energy. The aerobic system therefore can last indefinitely. Glucose, fatty acids and amino acids are combined with oxygen to release a lot of energy which can be used to convert AMP and ADP into ATP. Metabolic recovery can also occur, where lactic acid is converted into glucose and then into glycogen. The restoration of the aerobic system depends on carbohydrate in the diet and requires 48 hours to move this glucose into the system.

Describe oxygen debt. How fast is oxygen used following heavy exercise? How much oxygen must be consumed for the phosphagen and lactic acid system? What are the terms used to describe the early and latter parts of the oxygen debt?

The body stores 2L of oxygen which can be used. Oxygen is used within a minute for aerobic metabolism after heavy exercise. Therefore, 9L more oxygen must be consumed for the phosphagen and lactic acid system. All of this oxygen that has to be repaid is called the oxygen debt. The early portion of oxygen debt is called the alactacid oxygen debt (3.5 litres), whereas the lactic acid oxygen debt refers to the latter part of the oxygen debt (8 litres).

How do the sympathetic and parasympathetic systems affect blood flow? How much can blood flow increase during strenuous exercise? What is 1/2 of this increase caused by?

The cardiovascular system is responsible for delivery oxygen and nutrients to the muscles involved during exercise. The parasympathetic system causes constriction in areas where blood flow is not required, and the sympathetic system causes dilation in areas which required increased nutrients and oxygen during exercise. Blood flow can increase to a maximum of around 25-fold more during the most strenuous exercise when compared to resting blood flow. Almost ½ of this increase results from intramuscular vasodilation caused by the direct effects of increased muscle metabolism.

What is the phosphagen energy system? How much energy does this provide?

The combined amounts of cell ATP and cell phosphocreatine are known as the phosphagen energy system. This system provides enough energy to allow 8-10 seconds of maximal work, and therefore is used for maximal short bursts of muscle power.

Describe the distribution of fast and slow twitch fibres within athletes.

The distribution of fast and slow twitch fibres is determined almost entirely by genetics. This proportion could somewhat determine types of athletic prowess. These relative proportions seem to be almost entirely determined by genetics. Jumpers and sprinters have a greater number of fast-twitch fibers than other individuals. Marathon runners have a greater number of slow-twitch fibers than other athletes.

How does oxygen-diffusing capacity change between resting and maximal exercise?

The most startling factor about these results is the several fold increase in the diffusing capacity between the resting state and the state of maximal exercise. This finding results mainly from the fact that blood flow through many of our pulmonary capillaries is quite resting/sluggish in the resting state, whereas in maximal exercise, increased blood flow through the lungs causes all these pulmonary capillaries to be perfused at their maximal rates, providing far greater surface area through which oxygen can diffuse through the pulmonary capillary blood. This enables oxygen to be transported to the areas which require it within the body. Athletes which require greater volumes of oxygen per minute actually have higher diffusing capacities.

What else accounts for increased blood flow during exercise?

The remaining increase results from multiple factors, the most important of which is the moderate increase in arterial blood pressure which occurs in exercise, which is usually about a 30% increase. This increase in blood pressure forces more blood through the vessels, and stretches the walls of the arterioles, reducing the vascular resistance. Therefore, this 30% increase can usually about double the blood flow.

What is the limiting factor in regard to oxygen delivery?

The respiratory system is not normally the limiting factor in regard to the delivery of oxygen to the muscles during maximal muscle metabolism. Therefore, the ability of the heart to pump blood is actually the greater limiting factor.

What is the restoration of glycogen dependent on?

The restoration of glycogen is dependent on diet. 1. A high-carbohydrate diet is important before an athletic event. 2. Athletes should not participate in exhaustive exercise during the 48 hours preceding the event.

What determines the strength of the muscle? What is the value of the maximal contractile force? What is the value of the holding strength?

The strength of the muscle is determined mainly by its size. The maximal contractile force of muscle is between 3 and 4 kg/cm2 of the muscle cross-sectional area. The holding strength is 40% greater than the contractile strength. The holding strength is if a muscle is already contracted and a force is applied to attempt to stretch out the muscle even more, this requires approximately 40% more force than is achieved by simply shortening the contraction.

Describe the relationship between oxygen consumption and total respiratory ventilation. When you exercise more, how does this affect the volume of oxygen?

This figure (above) shows the relationship between oxygen consumption and total respiratory ventilation (L/min). There is a linear relationship between these two factors, which both increase about 20-fold between the resting state and maximal exercise in a well-trained athlete. When you exercise more, you are breathing more and therefore use a greater volume of oxygen.

What is VO2 max and when does it occur? How does training affect VO2 max?

VO2 max is the rate of oxygen usage under maximal aerobic metabolism, and it occurs when pulmonary ventilation is at 60-70%. Training will only increase VO2 max by 10%. The frequency of training (2 vs. 5 times a week) also has little effect on the increase in VO2. However, the VO2 max of a marathon runner is almost 40% greater than that of an untrained person. The explanation for this is that VO2 max is most likely genetically determined. People who have greater chest to body size ratios with stronger respiratory muscles are more likely to become marathon runners. Training over the course of many years may also compound the increase of VO2 max. Blood gases in max work are normal, except for pH.