This is normally limited by the size of the individual and thus the size of the thorax. Structure of muscle glycogen. Forced vital capacity may increase slightly and this is likely a response of the respiratory muscles to training rather than a change in lung size per se. At this pbysiology the subject was given grams of glucose and then was able physiologyy exercise for a further 40 minutes before exercise physiology book pdf free download ensued. The impulse can only be conducted in one direction and each neuron will contain only one type of neurotransmitter.
 
 

 

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Free Medical Books Download Physiology. In order to do this the muscle is also dependent upon the ability of the circulatory system to deliver oxygen to the tissue, and the ability of the tissue to extract and utilize the delivered oxygen. Either way exercise physiologists refer to this work rate, or this percentage of maximal capacity, as exercise intensity. METs are described below. Other exercise domains are described for work undertaken above or below the lactate threshold the point at which lactate begins to accu- mulate in the blood: see Section B5.

Work rates below the lactate threshold are referred to as moderate exercise, whilst those above the lactate threshold but below maximal oxygen uptake are referred to as being heavy exercise. Energy Measurement of energy expenditure allows the exercise physiologist to calcu- expenditure late the metabolic cost of exercise see also Section J1. Consequently, assessing energy expended during exercise in kilocalories, or the SI units of Joules, provides a measure of the physiological cost of producing physical work.

Heat produced during metabolism can be measured in a whole body chamber by direct calorimetry. As work rate increases VO2 increases linearly for moderate work rates those below the lactate threshold. Expired air is collected in Douglas bags, or sampled directly with an on-line gas analyzer, and the fractions of expired oxygen FEO2 and carbon dioxide FECO2 in the expired air measured. The volume of air expired per minute is usually measured via a dry gas meter, and is then recorded as the minute ventilation, or volume expired VE.

Dry gas meters usually possess internal thermometers in order that the temperature of the expired air can be recorded. When the air in the Douglas bag has been sampled for O2 and CO2, and the quantity of air, and temperature of air in the bag have been measured, all the student now requires in order to complete the calculation of oxygen uptake is the room temperature and atmospheric temperature, pressure and relative humidity.

So, oxygen uptake is calculated using the volumes that were recorded at atmospheric A temperature T and pressure P. These volumes would also be saturated S with water vapor. Thus they are said to be measured at ATPS. Thus the corrected volume is said to be recorded as STPD. During weightbearing activity such as running, the oxygen cost of the activity is expressed in relative terms.

If the weight is supported, as in cycle ergometry, it is usual to report oxygen cost in absolute terms. The total oxygen cost of movement incorporates the oxygen cost of rest, the oxygen cost of moving the legs in cycle ergometry, or the whole body in tread- mill exercise, plus the oxygen cost of performing work.

The true oxygen cost of performing work is thus the oxygen cost above that of rest and leg or body movement. On the cycle ergometer the oxygen cost of moving the legs is meas- ured during cycling against a zero load 0 W. The oxygen cost of performing the additional work is then measured as the difference between the oxygen uptake measured at a given work rate and that recorded at 0 W.

The maximal rate that the body can consume oxygen during physical activity at sea level is termed maximal oxygen consumption or uptake. This value can be measured from a maximal oxygen uptake exercise test, or predicted from a submaximal test see Section L. Maximal tests involve incremental activity, on any ergometer, whereby the subject exercises at increasing work rates until voli- tional fatigue. Caloric cost The caloric cost of exercise provides an estimation of the metabolic energy utilized in producing skeletal work.

However, the approximation of 5 kcal 20 kJ allows the exercise physiologist to estimate the caloric cost of an exercise session and compare it to the measured caloric intake in diet. Weight-loss programs are designed and assessed using this protocol see Section J.

Metabolic The metabolic equivalent MET provides a generic unit of energy expenditure. The energy sources for the high- intensity exercise are mainly derived from anaerobic sources whereas low- intensity exercise derives its energy mainly from aerobic processes. Creatine phosphate Creatine phosphate or phosphocreatine PCr is a high-energy phosphate molecule found in cells which is an immediate source of re-forming ATP from ADP.

Muscle glycogen Muscle glycogen is the storage form of carbohydrate, and is made up of glucose molecules. Glycogen can be broken down rapidly to produce ATP for intense exercise or more slowly for prolonged exercise. Glycogenolysis and Glycogenolysis is the process of removing glucose subunits from a glycogen glycolysis molecule.

The enzyme, glycogen phosphorylase, breaks off glucose molecules to form glucosephosphate. Glycolysis is the process of converting glucose to pyruvic acid in the cytoplasm of cells, with a net production of ATP. The process does not require oxygen, and whereas during steady-state exercise most of the pyruvic acid is processed through aerobic breakdown, during high-intensity exercise the resultant formation of lactic acid occurs.

Blood glucose Blood glucose is a carbohydrate source of energy for cells. The glucose in blood arises from the liver. Aerobic energy Aerobic energy is produced in the mitochondria of cells.

During prolonged systems exercise, the two major sources are carbohydrates and lipids. Related topics Fiber types C4 Macronutrients G2 The energy Examination of the major energy contribution from varying sources as the dura- continuum tion of exercise progresses can be seen in Fig.

At the start of an activity the initial source of energy is from the adenosine triphosphate ATP stores at the muscle crossbridges. Creatine phosphate PCr rapidly replaces the ATP and so, in an indirect sense, becomes the next major source of energy.

Schematic of the energy continuum. It is important to note that each of these mechanisms of energy production occur simultaneously. The energy continuum depicts the changes in major energy sources with time when exercise is maximal for each of the phases. Understanding of the energy continuum enables coaches and athletes to appreciate the major energy sources being used when exercising maximally in short or repetitive sprints during training or in games.

ATP Adenosine triphosphate ATP is a ubiquitous high-energy phosphate which consists of a nucleoside, adenosine, to which is attached three phosphate mole- cules using high energy-yielding bonds Fig. When a phosphate is removed from ATP, the energy produced provides the currency to enable muscles to move, molecules to be synthesized or to be transported against a concentration gradient or to be excreted.

Indeed, any energy requiring processes invariably uses ATP as the prime source of energy. Schematic of a the structure and, b hydrolysis of ATP. B1 — Energy sources and exercise 13 The amount of ATP in muscle is rather small, with the concentration being approximately 20—30 mM kg—1 of dry muscle. Clearly this is not the case, because maximal efforts last longer, and so the restoration of ATP must occur.

Creatine The other immediate source of energy for high intensity exercise is that of crea- phosphate tine phosphate or phosphocreatine PCr. PCr is also a high-energy phosphate in which a single phosphate molecule is attached to a molecule of creatine. The two best exam- ples from a muscle and exercise context are CKmm the form of creatine kinase found at the muscle crossbridge and CKmito the mitochondrial form of creatine kinase.

Whereas CKmm favors the above reaction from left to right, the isoform CKmito favors the reaction from right to left. The hydrolysis of PCr occurs during intense bouts of exercise at the crossbridges whilst resynthesis of PCr from creatine and ATP occurs during recovery phases at the mitochondrial membrane Fig. Schematic of the use and resynthesis of creatine phosphate. Section G explores the potential of creatine supplementation as an ergogenic aid. Muscle glycogen Muscle glycogen is an essential store of carbohydrate fuel for both high- intensity exercise and also prolonged activity.

Glycogen is a polysaccharide made up of a large number of monosaccharide glucose units joined together by two types of bonds i. The former produce straight chains of glucose molecules but after every ten glucose units or so, the chain is branched by the 1,6 bond. The process of breaking off glucose molecules from glycogen is known as glycogenolysis. The initial glucose product is glucosephosphate, which is then converted to glucosephosphate.

Once GP has been produced, there is a common pathway through glycolysis from the glucose removed from glycogen and glucose entering the cell from blood. Glycolysis is a series of processes which takes place in the cytoplasm of cells resulting in the formation of two pyruvic acid molecules and ATP. Structure of muscle glycogen. B1 — Energy sources and exercise 15 the pyruvic acid leads to the formation of lactic acid, although during steady- state exercise the majority of the pyruvic acid formed is broken down via the aerobic pathway to produce carbon dioxide and water.

Blood glucose Glucose delivered to the muscle by blood may also act as a useful energy source during exercise. The normal blood glucose concentration is around 5 mM, but can be elevated to values in excess of 7—8 mM hyperglycemia following a high carbohydrate meal or reduced to values lower than 4 mM hypoglycemia if exercising for prolonged periods of time without carbo- hydrates being ingested.

The glucose in blood is produced by the liver either from glycogenolysis of its own glycogen stores or from gluconeogenesis, where the glucose is produced from precursors such as lactic acid, alanine, pyruvic acid, or glycerol. Schematic showing overall processes of glycogenolysis and glycolysis.

The essential systems requirement is that oxygen must be present to complete the process. During steady-state exercise the pyruvic acid produced is converted to acetyl-CoA in the mitochondria and then undergoes aerobic oxidation via the TCA cycle. Fats are another major source of energy during prolonged exercise and can only be used to produce energy using aerobic processes. Essentially fats are converted, through b-oxidation, to produce acetyl-CoA and then enter the TCA cycle.

Hence acetyl-CoA is an important crossroad in carbohydrate and fat metabo- lism. For further details on the biochemistry of these processes you would be advised to consult Instant Notes in Biochemistry.

Schematic to show aerobic processes. The energy sources include ATP, PCr, power glycolysis, and the aerobic oxidation of carbohydrates and lipids. The maximal rate of ATP generation if employing PCr is dependent on the maximal rate of creatine kinase activity. The maximal rate of power generated through glycolysis is dependent on the maximal rate of the rate-limiting enzyme.

In the case of glycolysis, the rate-limiting enzyme is PFK. TCA cycle The maximal rate of energy production using the aerobic breakdown of carbohydrates is dependent on the slowest rate of ATP production from glycolysis or the TCA cycle.

The maximal rate of ATP generated through aerobic processes when using lipids is half that of carbohydrates. Related topics Fiber types C4 Nutrition and ergogenic aids for Integrated control of exercise F3 sports performance Section G Rate of ATP The maximal rate of ATP production is related to the power developed during production and a bout of exercise and is dependent on the maximal rates of ATP utilized by the power muscle.

These energy sources include those contained within the energy contin- uum, i. ATP, PCr, breakdown of muscle glycogen rapidly resulting in lactic acid formation, and the aerobic oxidation of carbohydrates and fats. In a test of power such as the Wingate test, the power produced is due to the rapid energy production from four sources of energy which will be highlighted below.

Examination of a typical power curve produced when undertaking the Wingate test Fig. Each of the energy-producing processes involved in the generation of power for a Wingate test has maximal rates of ATP production. Experiments which have used muscle biopsy before and after maximal-inten- sity exercise of varying durations have resulted in the data obtained for Table 1.

In order to achieve this, a subject would have a muscle biopsy undertaken at rest and this would be followed by a further biopsy taken immediately after an all-out bout of exercise lasting for between 6 and 60 s.

Since the exercise lasts for 6 s the rate of use may be calculated. Likewise, this process can be repeated for bouts lasting 10, 20, 30 and 60 s. Interestingly, the maximal rate of ATP use from anaerobic glycol- ysis is approximately half that for PCr degradation.

This is because the rate-limiting enzyme for glycolysis is PFK phosphofructokinase , which has a lower activity than CK. TCA cycle The two major aerobic energy processes shown in Table 1 i.

Although these rates of production are relatively low, the total amount of energy from these aerobic stores is larger. From Table 1 it is evident that carbohydrates can produce ATP at twice the rate that fats can be maxi- mally oxidized.

The total amount is approximately — g in the liver and — g in muscle, although diet and exercise can alter these amounts substantially. Lipids Lipids are mainly stored in adipose tissue as triglycerides, a combination of three fatty acids with a glycerol molecule. However, muscle triglyceride stores are also present. Protein Muscle is the largest source of protein that can be used as a fuel during exercise.

The total amount available is therefore dependent on the muscle mass. Related topics The endocrine system F2 Energy balance J1 Nutrition and ergogenic aids for sports performance Section G Carbohydrates Carbohydrates are an important energy source for both intense and prolonged exercise, and are stored as glycogen in both the muscle where it is needed as an energy source and in liver where the glucose is pushed out into the blood.

In comparison with lipid stores, carbohydrates are limited with a total amount of approximately g in the body. The muscle contains around g of glyco- gen, although this store can increase to or g when carbohydrate loaded, whilst the liver glycogen stores are about g in total. The liver glycogen stores are also affected by diet and exercise in so far as these stores are enhanced by high carbohydrate feeding and depleted by either prolonged exercise or fasting.

Indeed, after an overnight fast the liver glycogen stores can be severely depleted. The amount of energy contained within the carbohydrate stores can be esti- mated by multiplying the total amount in grams by 3.

Therefore a g muscle glycogen content contains kcal or kJ of energy. Glycogen is produced from glucose carried to the muscle or liver in blood and is regulated by the hormone, insulin. Normally this process arises after ingesting a meal containing carbohydrates.

Increased levels of circulating blood insulin result in enhanced uptake of glucose by muscle and the subsequent packaging of the glucose to existing glycogen to make a larger glycogen mole- cule.

The key enzyme responsible for this process of glycogenesis is glycogen synthase. Schematic to show the process of glycogenesis. Lipids Lipid stores are, in contrast to carbohydrates, a major store of energy, since each fat molecule contains 9 kcal 38 kJ of energy. This is more than twice the energy density found in carbohydrates and so makes lipids a useful, compact storage source. Lipids are stored as triglycerides, which are essentially a glycerol molecule that is attached to three fatty acids Fig.

Major stores of triglycerides can be found in adipose tissue, although they may also be found inside muscle cells. Although triglycerides are the storage form of lipids, fatty acids are the useable form from a metabolic perspective. Triglycerides are produced when there is an excess amount of fat intake or when there is an excessive amount of carbohydrate ingested.

The fatty acids from the digested food become attached to a glycerol molecule to produce triglycerides. In the case of excessive amounts of carbohydrate ingested, the glucose is used to produce both glycerol and fatty acids, which together make up a triglyceride molecule. Triglyceride molecule. Such a calculation shows that the energy content is 94 kcal or kJ, a plentiful supply of energy.

Protein The major stores of metabolic protein are muscles. Of course proteins include all enzymes, peptide hormones, molecules such as hemoglobin and myoglobin, and are an integral part of all membranes.

However, these sources are not broken down to be used as energy. The total mass of potentially usable protein is about 8 kg, although this depends on the muscle mass of an individual. Protein provides 4 kcal 17 kJ of energy per gram, and so if there were 8 kg of protein, this would provide 32 kcal kJ of energy. The problem with using protein as an energy source is that it means the muscle is cannibalizing itself to provide energy.

The control is mediated by hormones which, via cAMP, activate inactive enzymes. However, enzyme activity can also be affected by allosteric effectors. Cyclic AMP activates a protein kinase within cells, which in turn activates inactive enzymes. In some instances e. Production of cAMP occurs as a consequence of hormonal activation. Allosteric effectors Some molecules found in cells are able to promote or inhibit the activity of regulatory enzymes. Such molecules, known as allosteric effectors, do not bind to the active site of an enzyme and as such are distinct from competitive inhibitors.

Related topics The endocrine system F2 Integrated control of exercise F3 Metabolic To ensure that ATP is provided rapidly or slowly, there needs to be regulation regulation of the metabolic processes.

Such regulation is normally controlled during steady-state exercise by circulating hormones secreted by endocrine glands such as the adrenal glands or the pancreas. The hormones secreted by these glands include adrenaline epinephrine , noradrenaline norepinephrine , glucagon, and insulin, and they mediate their effects by activating inactive enzymes present within the cell. However if the exercise is intense and rapid, there may be no opportunity for hormones to regulate such activity as energy is required within seconds.

Under these circumstances the switching on of energy processes must take place due to activation within the cell. Hormones and There are essentially three classes of hormones, these being amine hormones, cyclic AMP peptide hormones and steroid hormones.

The amine hormones include the catecholamines adrenaline epinephrine and noradrenaline norepinephrine , the peptide hormones include glucagon and insulin, whereas the steroid hormones include the sex hormones estrogen and testosterone. Peptide and amine hormones affect their target cells by attaching to a receptor on the plasma membrane and switching on the production of cyclic AMP cAMP.

Once the inactive enzymes are activated, they undertake their metabolic role. The breakdown of triglycerides leads to the formation of fatty acids and glycerol, and is known as lipolysis. The key hormones concerned with regulating energy metabolism are the amine and peptide hormones, although the steroid hormones cortisol and growth hormone also affect metabolic processes.

These hormones have as their target tissues either muscle, adipose tissue or liver, and regulate the processes glycogenolysis, glycolysis, lipolysis, gluconeogenesis, and glycogenesis, as well as protein degradation and synthesis. Table 1 shows which processes are affected by the hormone in these tissues. Schematic to show regulation of glycogen phosphorylase activity. Schematic showing regulation of lipolysis in adipose tissue or muscle cells.

Allosteric The metabolic processes involved in energy production and storage are effectors regulated by hormones. Under such circumstances it is unlikely that hormones such as adrenaline epinephrine can switch on glycogenolysis quickly enough, and so there is a need to switch on glycogen phosphorylase more rapidly. Such an activation or inhibition of an enzyme by a cell product is an example of allosteric regulation.

Allosteric regulators include ATP, ADP, ammonia, citric acid, and products of the process being catalyzed by the enzyme itself. Examples of allosteric effectors: a control of glycogen phosphorylase, b control of PFK activity. Muscle glycogen is broken down in the cytoplasm during intense exercise to produce energy and lactic acid. Prolonged Muscle and liver glycogen stores are used to provide energy during prolonged steady-state exercise exercise.

Intermittent exercise Carbohydrates are an important source of energy during intermittent bouts of exercise, in particular the more intense intervals. Related topics Fiber types C4 Nutrition and ergogenic aids for The endocrine system F2 sports performance Section G High-intensity High-intensity exercise is exercise that is non-steady-state exercise, and as such exercise is likely to be maintained for slightly longer than 5 minutes before fatigue ensues. This means that such exercise can be maximal and last for a few seconds or slightly more prolonged.

All these energy sources reside in the cytoplasm and can be used rapidly from processes that take place in the cytoplasm. Fats are unable to be used for such intense exercise because they are only broken down in the mitochondria. In spite of much of the early evidence reported to show an impact of lactic acid accumulation on fatigue, there are several more recent studies which demonstrate that lactic acid is not the only fatiguing factor.

Increases in inor- ganic phosphate Pi as well as reductions in PCr are important factors relating to fatigue during high-intensity exercise. Although lactic acid is considered to be a problematical product of high- intensity exercise, the measure of blood lactic acid concentrations at varying exercise intensities has proved to be a most valuable indicator of aerobic capac- ity.

The exercise intensity at which such prolonged exercise can be maintained is often associated with the lactate threshold. The lactate threshold is an exercise intensity above which there is a likely gradual increase in lactic acid. This is known as the lactate threshold. From Fig. The lactate threshold occurs for a number of reasons. As exercise intensity increases the rate of glycolysis increases above that of the TCA cycle and hence more of the pyruvic acid formed is converted to lactic acid.

As exercise intensity increases there is a limited delivery of oxygen to muscle and hence a greater chance of anaerobiosis. B5 — Energy for exercise of varying intensities 29 The reasons why the lactate threshold graph shifts to the right are because endurance training results in: 1. Prolonged steady- The exercise intensity enabling prolonged activity is dependent on the level of state exercise training.

The major energy source during such exercise is initially carbohydrate from muscle glycogen and blood glucose, but as the exercise progresses there is a greater dependence on fatty acids either from intramuscular triglyceride stores from adipose tissue. Increases in adrenaline epinephrine and a fall in insulin result in these changes. A simple way of determining the contribution of carbohydrate and fat to total oxidation is by measuring oxygen uptake and the respiratory exchange ratio RER.

The latter is also referred to as the respiratory quotient RQ. Change in RER at varying exercise intensities. Fatigue for prolonged exercise is due to hypoglycemia, muscle glycogen depletion, or dehydration.

It also shows that a low muscle glycogen concentra- tion results in an attenuated time to exhaustion. At this time the subject was given grams of glucose and then was able to exercise for a further 40 minutes before fatigue ensued.

At the second point of fatigue, blood glucose was above 4 mM and so hypoglycemia could not have been the cause. Relationship between diet, muscle glycogen and exercise capacity. Blood glucose concentration over time during a test to fatigue. Intermittent Many sports require the athlete to engage in repeated bouts of high-intensity exercise activity with lower levels of activity. This means that the majority of the energy arises from carbohydrate and fat stores.

Use of match analysis techniques, by analyzing video footage of sports, leads to a greater understanding of the game demands and an awareness of the over- all intensities and types of activities in that sport.

Fatigue during intermittent exercise is likely to result from hypoglycemia, muscle glycogen depletion, and dehydration as for prolonged exercise, although in addition any gradual and sustained increases in lactic acid concentrations during the intense activity phases may also be a factor.

It can be seen that of the soccer players who started the match with a low muscle glycogen content the distance covered in the second half of the game and the ability to sprint was severely diminished.

This is known as adaptation. It may be continuous or intermittent. Sprint training This form of training enhances the anaerobic capacity and power generative capacity of muscles.

Sprint training normally involves repeated efforts at a high exercise intensity. Related topics Adaptations to training C5 The endocrine system F2 Cardiovascular responses to Training for performance Section H training E4 Adaptation Adaptation occurs in muscles as a consequence of repeated bouts of exercise over a period of time. Sprint training Sprint training involves repeated bouts of high-intensity efforts interspersed with appropriate recovery periods see Section H. The type of energy source used for each sprint bout is dependent on the time i.

The resultant effect is that the enzyme activity for that energy source is enhanced with training, i. This membrane acts to control active and passive transport into the cell. The sarcoplasm houses the cell nuclei, sarcoplasmic reticulum and the contractile apparatus.

Triad A single transverse tubule and two terminal cisternae sacs of the sarcoplasmic reticulum form a triad. The triad aids rapid communication between the sarcolemma and the contractile apparatus.

Related topics Fiber types C4 Cardiovascular structure E1 Adaptations to training C5 Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement.

The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these func- tions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.

A single muscle, as seen in Fig. The gross structure of skeletal muscle. Within the groove of this helix structure sit two strands of the protein tropomyosin, upon which at regu- lar intervals sits the protein troponin. The troponin complex includes three subunits: a troponin I, which binds to actin, b troponin C, which binds to calcium ions, and c troponin T, which binds to tropomyosin.

Myosin has a two-chained helical tail, that at one end terminates in two large globular heads. These heads, during contraction, are referred to as cross-bridges and contain an ATP-binding site that is imperative for muscle contraction to occur. Triad The sarcoplasm also contains a hollow membranous system that is linked to the sarcolemma and assists in conducting neural commands through the muscle.

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