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Fuel for exercise

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Radhika Chintamani
Radhika Chintamani

every exercises contains different types of fuel, so this ppt describes what fuels are needed for exercises

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Fuel for Exercise: Bioenergetics and Muscle metabolism Radhika Chintamani All energy originates from sun as light energy. Chemical reaction in plants producing energy for themselves is called photosynthesis. Human produce energy required by body by certain processes where substartes can be broken down into simple compound so that they can be easily obtained as energy. This mechanism of breaking down the substrates into simpler form and store them as energy is called as bioenergetics, whereas all the chemical process of conversion of molecules into energy and formation of energy is called metabolism. Humans consume variety of diet which mainly compromise of carbohydrates, fats, proteins, minerals, vitamins, and water. Human body is mainly made up of 60% water and 40% solid. In this 40% of solid weight, it includes, fat mass and muscle mass (carb and protein and little amount of fat). Energy: It is the fuel required for doing daily activities. Energy in biological system is measured by calorie (unit=kCal). Calorie: one calorie by definition is amount of energy required to heat 1g of water and raise its temperature by 10 C, i.e. from 14.50 to 15.50 . Energy substrates: When food enters body, it undergoes various pathways of chemical degradation at various stages in G.I.T. Food is consumed whole and sole, i.e. there cannot be separation of carbohydrate, protein, and fat content separately in every food item, hence the individual has to consume all of these substarte together. Substarte is composed of carbon, hydrogen, oxygen and nitrogen(in case of protein). When an individual eats the food, the process of digestion starts at chewing stage, then bolus formation, then the food undergoes peristaltic action of the esophagus wherein slowly the food enters the stomach, where it undergoes acidification of the food by Hcl, and then important contents needed by the body are sent to liver, where the food gets metabolized, and stored, pancrease where the insulin secretion takes place, and the non-important part is excreated via, small intestine (urine) and large intestine (stools). The food particles when metabolized yield energy in an important form called as ‘’ATP’’. ATP’s are the small energy packets. Controlling the rate of energy production Free energy must be released from the substrate in the form of energy at a controlled rate in order to utilize it properly. This rate is primarily determined by 3 things; i. Availability of the primary substrate: availability of substrate is directly proportional to the energy production rate. Greater amount of energy leads to high amount of energy production. Mass action effect: influence of substarte availability on the rate of metabolism is called so.
ii. Amount of Rate limiting enzyme available: rate limiting enzyme is the enzyme which controls the amount of energy production from the primary substrate via a negative feedback (the end product of the chemical reaction, if obtained in a very huge amount then, it inhibits the first step of the chemical reaction) and sometimes enhance the production of energy via a positive feedback (the end product if is obtained in a small quantity, the end product fascilitates the chemical reaction by fascilitating the rate limiting enzyme). iii. Enzyme activity: enzyme activity is basically the process by which the enzyme guards the chemical reaction. Many chemical reaction needs some enzyme in order to break the substrate into parts. This enzyme names usually end with the lyase, which usually means breaking or splitting. Not all reaction needs enzyme, some reaction takes place without any assistance with external factor, e.g: water readily splits into 2H+ and O2. iv. Activation energy: the energy required to begin any chemical reaction is called so. Some enzymes speed up the reactions by lowering the activation energy. v. Cofactors: the factors which help the enzyme to complete its function are called so. Some enzyme needs assistance in order to completely carry on the reaction, the substance required is known as cofactor. Storing Energy: high- energy phosphates: Immediately available source of energy for almost all metabolism including muscle contraction is adenosine triphosphate, or ATP. ATP (low-energy compound) is formed by the fusion of adenosine diphosphate and a high energy phosphate group. ATP can be generated in 2 ways: i. ATP generated independent of oxygen availability is called as substrate level phosphorylation. ii. ATP generated in the presence of oxygen is called oxidative phosphorylation. 1 mole of ATP under standard conditions, produces approximately 7.3kcal of energy. (It’s possible to produce about 10kcal of energy from 1 mole of ATP.) Basic energy systems: Cells generate energy via 3 different systems: 1. ATP-PCr system. 2. Glycolytic system (glycolysis). 3. The oxidative system (oxidative phosphorylation)= aerobic system. ATP-PCr system will be described below, whereas rest systems will be described under the substrate of their own chemical reaction. ATP-PCr reaction: ATP=Adenosine triphosphate=low energy phosphate molecule. Anaerobic metabolism
 Formation by fusion of ADP and free phosphate. Phosphocreatinine= high energy phosphate molecule found in cell. Pathway: Pi is donated from the PCr to ADP to form ATP. This Pi is the activated phosphate. Energy released by breakdown of PCr is not directly used for cellular work. Instead, it regenerates ATP to maintain a relatively constant supply of ATP under resting condition. Rate limiting enzyme: Creatinin kinase. Also works on the principle of the negative feedback principle. It catalyses the first step i.e. release of energy from PCr molecule. This reaction occurs in the absence of oxygen, hence termed as substrate level phosphorylation. During the first few seconds of intense muscular activity, such as sprinting, ATP is maintained at a relatively constant level, but PCr declines steadily as it is used to replenish the depleted ATP. However, at exhaustion both ATP and PCr levels are low and are unable to provide energy for further muscle contraction and relaxation. The combination of ATP-PCr stores can sustain the muscles energy needs only for 3s-15s during an all- out sprint. Beyond that time, muscles must rely on other process like: glycolytic and oxidative pathways. Carbohydrates: Atoms of carbon, hydrogen and oxygen combine to form a basic carbohydrate (sugar) molecule. General formula: (CH2O)n, where n=range from 3 to 7 carbon atoms with hydrogen and oxygen attached via single bond. Types of carbohydrates: Monosaccharides i. Glucose ii. Fructose iii. Galactose Disaccharides: i. Sucrose (glucose+fructose) ii. Lactose (glucose+galactose) iii. Maltose (glucose+glucose) Polysaccharides i. Plant: starch (amylose and amylopectin), fibers, All carbohydrates are ultimately converted to glucose that is transported through blood to all body tissues. The glucose remaining after utilization from all tissues of the body, is stored in liver as liver glycogen, which is re-synthesized later converting it into glucose for use in future. Hence, under resting condition glucose is stored as glycogen. Glycogen is stored in two different places, i.e. muscle=muscle glycogen and liver= liver glycogen. Muscle has limited amount of
storage as compared to liver, hence when the muscle storage gets over, the glycogen is synthesized to glucose and is transferred to muscle from liver via blood. Function: a. Main source of energy for light-to-moderate intensity exercise. b. Regulates body’s protein and fat metabolism. c. Nervous system relies exclusively on presence of carbohydrate. d. Prevents ketosis. e. Serve primary energy for formation of RBC’s. Sources: depending on Glycemic index: a. High carb diet [G.I.>70]: Sports drink, jelly bean, baked potatoes, French fries, pretzels, etc. b. Moderate carb diet [ G.I. =56-70]: Pastry, pita bread, boiled rice, banana, regular ice- cream. c. Low carb diet [G.I<55]: Yoghurt, grapefruit, milk, apple, pears, peanuts, kidney and baked beans. -These food items were classified according to 2002 ‘’International Table of Glycemic Index and Glycemic Loading’’. Carbohydrate consumption, its usage and its breakdown: 3 cycles break down carbohydrate into glucose: a. Glycolytic system: via Glycogenolysis. b. Oxidative system: via Glycolysis and Kreb’s cycle. Glycogenolysis: formation of gluose from the other substrates such as proteins or fats.???? Glycolysis: liberation of ATP (energy) by breaking down of glucose molecule. It is named as glycolytic pathway as this pathway entails breaking down of glucose via various glycolytic enzymes.
Glucose Glycogen Stored in 2 places; - In Liver as liver glycogen. - In muscle as myoglycogen. Glycolysis requires 10-12 enzymatic reactions for the break down of pyruvic acid. The fate of pyruvic acid depends on whether the reaction is oxidative(the end product enters kreb’s cycle.) or non-oxidative(pyruvic acidelactic acidlactate). Reaction: Glycogenesis Glycogen glucose-1-phosphate enters glycolysis pathway glycogenolysis. Glucose Glucose-6-phosphate Glucose-1-phosphate Glucose Fructose-6-phosphate Fructose 1,6, diphosphate Dihydrxyacetone phosphate 2,(3 phosphoglycceraldehyde) 2(1,3 diphosphoglyceraldehyde) 2(3 phosphoglycerate)
Net gain from this process is each -Glycogen= 3 moles of ATP. -Glucose=2 moles of ATP. In all out sprint events lasting 1 or 2 min, demand on glycolytic system is high, and muscle lactic acid concentration increase from a resting value of about 1mmol/kg of muscle to more than 25mmol/kg of muscle. This acidification of muscle fiber, limits the further breakdown of the glycogen as it inhibits the function of glycolytic enzyme. Also, fiber decreases the calcium- binding capacity which impedes muscle contraction. Rate limiting enzyme: phosphofructokinase or PFK. Prolonged exercise relies on third system i.e. the oxidative system. Kreb’s cycle: It is the continuation of the glycolysis chemical reaction. Depending on the presence or absence of the oxygen, the fate of pyruvic acid is determined, i.e. in the presence of oxygen, the pyruvic acid enters the Kreb’s cycle to yield further more energy, whereas in the absence of the oxygen, the pyruvic acid gets converted to lactic acid which further reduces to lactate. Carbohydrate dynamics in exercise: During anaerobic exercise carbohydrate become the sole fuel for ATP synthesis. Carbohydrate availability in the food consumed controls its supply to ATP formation during exercise. Concentration of blood glucose provides biofeedback regulation of the liver’s glucose output: an
increase in blood glucose inhibits hepatic glucose release during exercise. Also, carbohydrate availability helps in fat mobilization and its use for energy. High intensity exercise:  Neural and hormonal factors during intense exercise increase the release of epinephrine, nor-epinephrine, and glucagon, where as decrease in insulin release. These hormonal responses activate glycogen phosphorylase which fascilitates glycogenolysis in the liver and muscle.  Muscle glycogen provides energy without oxygen during high intensity exercise training for 15-20min, later liver has to synthesize new glucose to fill in the exempted muscle glycogen and provides 40-50% of energy requirements, remaining is supplied by fat and protein catabolism.  An advantage of selective dependence on carb metabolism during intense aerobic exercise derives from its rate of energy transfer which is twice that of fat or protein. Moderate and prolonged exercise:  During low intensity exercise fat serves as the main energy substrate throughout exercise.  As submaximal exercise program increases progressively glycogen depletion is seen, and with time circulating fat increases and also their catabolism. Protein catabolism may also increase.  After certain amount of time, individual performing exercise gets exhausted and energy output decreases, this is when fat come into consideration. Fat oxidation provides energy in the later stage, the process being aerobic, is a slow process. *hitting the wall sensation: Effect of diet on muscle glycogen stores and endurance: Amount of storage of carbohydrate in muscle and liver=2500kcal to 2600kcal of energy. Lipids: Lipids ratio of hydrogen: oxygen exceeds that of carbohydrate, i.e. H:O=18.3:1. Approximately 98% of dietary lipids exists as triglycerol, while about 90% of the body’s total fat resides in the adipose tissue depots of the subcutaneous tissues. Types of lipids: Simple lipids Compound lipids Derived lipids a. Saturated fatty acids. b. Unsaturated fatty acids. c. Triacylglycerol a. High density b. Low density c. Very low density a. Simple lipids b. Compound lipids.
d. Trans-fatty acids e. Lipids in diet. d. Chylomicrons Simple lipids/ neutral fats:  Consists primarily of triacylglycerol.  No affinity to water.  Major storage form of fat in adipocytes.  Synthesis of triacylglycerol molecules produces three molecules of water. Types: a. Saturated fatty acids: - Single covalent bonds between carbon atoms, and all of the remaining bonds attach to hydrogen. - Occur primarily in animal products such as beef, lamb, pork, chicken, egg yolk, dairy fats of cream, milk, butter and cheese. - Also found in plant kingdome in: coconut and plam oil, vegetable shortening, hydrogenated margarine, cakes, pies, cookies. b. Unsaturated fatty acids: - One or more double bonds along their main carbon chains. - Types: monounsaturated fatty acids (single double bond) and polyunsaturated fatty acids (more than one double bonds). - The chemical process of hydrogenation changes oils to semisolid fats by bubbling liquid hydrogen under pressure into vegetable oil. - Hydrogenated oils behave like saturated fat. c. Triacylglerol: i. Triacylglycerol formation: by a process termed as eterification. Occurs in adipocytes. Synthesis increases because of 2 main reasons, i). food absorption increases blood levels of fatty acids and glucose. ii). relatively high levels of circulating insulin fascilitates triacylglycerol synthesis. ii. Triacylglycerol breakdown: by a process termed as hydrolysis (to yield glycerol and energy rich fatty acid molecule.). Occurs in adipocytes. The mobilization of fatty acids via lipolysis predominates under four condition: - Low-to-moderate intensity exercise. - Low-calorie-dieting or fasting. - Cold stress. - Prolonged exercise that depletes glycogen reserves. d. Trans-fatty acid (unwanted fatty acid): generated by partial hydrogenation of unsaturated corn, soyabean, or sunflower oil. It forms when one of the hydrogen atom along the restricted chain moves from cis position to trans position, hence called so. e. Lipids in diet: avg US. consumes about 15% of total calories as saturated fatty acids. Health professional worrying about the affect of saturated fatty acids on human body, found out two course of action: - Replacing at least a portion of saturated fatty acids and all trans fatty acids by nonhydrogenated monounsaturated and polyunsaturated oils.
- Balancing energy intake with regular physical activity to minimize weight gain and obtain the health benefits of regular exercise. - Consumption of more than 10% of total daily energy intake as saturated fatty acids is harmful. Compound lipids: Defnn of phospholipids. Glycolipids Lipoproteins Types of lipoproteins: a. High density: b. Low density: c. Very low density: d. Chylomicrons: FAT DYNAMICS DURING EXERCISE:  Intracellular and extracellular fats supply 30-80% of energy for physical activity depending on nutritional and fitness status and duration and intensity of exc. Exercise   Increased blood flow through adipocytes   Increases the release of FFA’s for delivery for use by muscle.  Long term consumption of high fat diet induces adaptation to the diet and hence utilization of fats as a source of energy during submaximal exc by fat oxidation process.  Usually fatty acids released provide energy in low-moderate intensity and greater duration exercise.  Aerobic training increases long-chain fatty acid oxidation during mild-to-moderate intensity exercise, primarily fatty acids from triglycerols within active muscles. Enhanced fat oxidation with training spares glycogen; this allows trained individuals to exercise at high levels of submaximal exercise before they experience fatigue.
High fat diet Low fat diet Adaptation to this kind of diet shows shift in use towards higher fat oxidation during rest and exercise. Prolonged increase in intake of high fat diet Decreases FFA mobilization from adipocytes to the active muscle It becomes detrimental to health of athlete in future. By reducing carbohydrate and increasing fat to about 30% produces a more optimal zone for endurance performance. Restricting dietary fats below the RDA, can also impair exercise performance.

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Fuel for exercise

  • 1. Fuel for Exercise: Bioenergetics and Muscle metabolism Radhika Chintamani All energy originates from sun as light energy. Chemical reaction in plants producing energy for themselves is called photosynthesis. Human produce energy required by body by certain processes where substartes can be broken down into simple compound so that they can be easily obtained as energy. This mechanism of breaking down the substrates into simpler form and store them as energy is called as bioenergetics, whereas all the chemical process of conversion of molecules into energy and formation of energy is called metabolism. Humans consume variety of diet which mainly compromise of carbohydrates, fats, proteins, minerals, vitamins, and water. Human body is mainly made up of 60% water and 40% solid. In this 40% of solid weight, it includes, fat mass and muscle mass (carb and protein and little amount of fat). Energy: It is the fuel required for doing daily activities. Energy in biological system is measured by calorie (unit=kCal). Calorie: one calorie by definition is amount of energy required to heat 1g of water and raise its temperature by 10 C, i.e. from 14.50 to 15.50 . Energy substrates: When food enters body, it undergoes various pathways of chemical degradation at various stages in G.I.T. Food is consumed whole and sole, i.e. there cannot be separation of carbohydrate, protein, and fat content separately in every food item, hence the individual has to consume all of these substarte together. Substarte is composed of carbon, hydrogen, oxygen and nitrogen(in case of protein). When an individual eats the food, the process of digestion starts at chewing stage, then bolus formation, then the food undergoes peristaltic action of the esophagus wherein slowly the food enters the stomach, where it undergoes acidification of the food by Hcl, and then important contents needed by the body are sent to liver, where the food gets metabolized, and stored, pancrease where the insulin secretion takes place, and the non-important part is excreated via, small intestine (urine) and large intestine (stools). The food particles when metabolized yield energy in an important form called as ‘’ATP’’. ATP’s are the small energy packets. Controlling the rate of energy production Free energy must be released from the substrate in the form of energy at a controlled rate in order to utilize it properly. This rate is primarily determined by 3 things; i. Availability of the primary substrate: availability of substrate is directly proportional to the energy production rate. Greater amount of energy leads to high amount of energy production. Mass action effect: influence of substarte availability on the rate of metabolism is called so.
  • 2. ii. Amount of Rate limiting enzyme available: rate limiting enzyme is the enzyme which controls the amount of energy production from the primary substrate via a negative feedback (the end product of the chemical reaction, if obtained in a very huge amount then, it inhibits the first step of the chemical reaction) and sometimes enhance the production of energy via a positive feedback (the end product if is obtained in a small quantity, the end product fascilitates the chemical reaction by fascilitating the rate limiting enzyme). iii. Enzyme activity: enzyme activity is basically the process by which the enzyme guards the chemical reaction. Many chemical reaction needs some enzyme in order to break the substrate into parts. This enzyme names usually end with the lyase, which usually means breaking or splitting. Not all reaction needs enzyme, some reaction takes place without any assistance with external factor, e.g: water readily splits into 2H+ and O2. iv. Activation energy: the energy required to begin any chemical reaction is called so. Some enzymes speed up the reactions by lowering the activation energy. v. Cofactors: the factors which help the enzyme to complete its function are called so. Some enzyme needs assistance in order to completely carry on the reaction, the substance required is known as cofactor. Storing Energy: high- energy phosphates: Immediately available source of energy for almost all metabolism including muscle contraction is adenosine triphosphate, or ATP. ATP (low-energy compound) is formed by the fusion of adenosine diphosphate and a high energy phosphate group. ATP can be generated in 2 ways: i. ATP generated independent of oxygen availability is called as substrate level phosphorylation. ii. ATP generated in the presence of oxygen is called oxidative phosphorylation. 1 mole of ATP under standard conditions, produces approximately 7.3kcal of energy. (It’s possible to produce about 10kcal of energy from 1 mole of ATP.) Basic energy systems: Cells generate energy via 3 different systems: 1. ATP-PCr system. 2. Glycolytic system (glycolysis). 3. The oxidative system (oxidative phosphorylation)= aerobic system. ATP-PCr system will be described below, whereas rest systems will be described under the substrate of their own chemical reaction. ATP-PCr reaction: ATP=Adenosine triphosphate=low energy phosphate molecule. Anaerobic metabolism
  • 3.  Formation by fusion of ADP and free phosphate. Phosphocreatinine= high energy phosphate molecule found in cell. Pathway: Pi is donated from the PCr to ADP to form ATP. This Pi is the activated phosphate. Energy released by breakdown of PCr is not directly used for cellular work. Instead, it regenerates ATP to maintain a relatively constant supply of ATP under resting condition. Rate limiting enzyme: Creatinin kinase. Also works on the principle of the negative feedback principle. It catalyses the first step i.e. release of energy from PCr molecule. This reaction occurs in the absence of oxygen, hence termed as substrate level phosphorylation. During the first few seconds of intense muscular activity, such as sprinting, ATP is maintained at a relatively constant level, but PCr declines steadily as it is used to replenish the depleted ATP. However, at exhaustion both ATP and PCr levels are low and are unable to provide energy for further muscle contraction and relaxation. The combination of ATP-PCr stores can sustain the muscles energy needs only for 3s-15s during an all- out sprint. Beyond that time, muscles must rely on other process like: glycolytic and oxidative pathways. Carbohydrates: Atoms of carbon, hydrogen and oxygen combine to form a basic carbohydrate (sugar) molecule. General formula: (CH2O)n, where n=range from 3 to 7 carbon atoms with hydrogen and oxygen attached via single bond. Types of carbohydrates: Monosaccharides i. Glucose ii. Fructose iii. Galactose Disaccharides: i. Sucrose (glucose+fructose) ii. Lactose (glucose+galactose) iii. Maltose (glucose+glucose) Polysaccharides i. Plant: starch (amylose and amylopectin), fibers, All carbohydrates are ultimately converted to glucose that is transported through blood to all body tissues. The glucose remaining after utilization from all tissues of the body, is stored in liver as liver glycogen, which is re-synthesized later converting it into glucose for use in future. Hence, under resting condition glucose is stored as glycogen. Glycogen is stored in two different places, i.e. muscle=muscle glycogen and liver= liver glycogen. Muscle has limited amount of
  • 4. storage as compared to liver, hence when the muscle storage gets over, the glycogen is synthesized to glucose and is transferred to muscle from liver via blood. Function: a. Main source of energy for light-to-moderate intensity exercise. b. Regulates body’s protein and fat metabolism. c. Nervous system relies exclusively on presence of carbohydrate. d. Prevents ketosis. e. Serve primary energy for formation of RBC’s. Sources: depending on Glycemic index: a. High carb diet [G.I.>70]: Sports drink, jelly bean, baked potatoes, French fries, pretzels, etc. b. Moderate carb diet [ G.I. =56-70]: Pastry, pita bread, boiled rice, banana, regular ice- cream. c. Low carb diet [G.I<55]: Yoghurt, grapefruit, milk, apple, pears, peanuts, kidney and baked beans. -These food items were classified according to 2002 ‘’International Table of Glycemic Index and Glycemic Loading’’. Carbohydrate consumption, its usage and its breakdown: 3 cycles break down carbohydrate into glucose: a. Glycolytic system: via Glycogenolysis. b. Oxidative system: via Glycolysis and Kreb’s cycle. Glycogenolysis: formation of gluose from the other substrates such as proteins or fats.???? Glycolysis: liberation of ATP (energy) by breaking down of glucose molecule. It is named as glycolytic pathway as this pathway entails breaking down of glucose via various glycolytic enzymes.
  • 5. Glucose Glycogen Stored in 2 places; - In Liver as liver glycogen. - In muscle as myoglycogen. Glycolysis requires 10-12 enzymatic reactions for the break down of pyruvic acid. The fate of pyruvic acid depends on whether the reaction is oxidative(the end product enters kreb’s cycle.) or non-oxidative(pyruvic acidelactic acidlactate). Reaction: Glycogenesis Glycogen glucose-1-phosphate enters glycolysis pathway glycogenolysis. Glucose Glucose-6-phosphate Glucose-1-phosphate Glucose Fructose-6-phosphate Fructose 1,6, diphosphate Dihydrxyacetone phosphate 2,(3 phosphoglycceraldehyde) 2(1,3 diphosphoglyceraldehyde) 2(3 phosphoglycerate)
  • 6. Net gain from this process is each -Glycogen= 3 moles of ATP. -Glucose=2 moles of ATP. In all out sprint events lasting 1 or 2 min, demand on glycolytic system is high, and muscle lactic acid concentration increase from a resting value of about 1mmol/kg of muscle to more than 25mmol/kg of muscle. This acidification of muscle fiber, limits the further breakdown of the glycogen as it inhibits the function of glycolytic enzyme. Also, fiber decreases the calcium- binding capacity which impedes muscle contraction. Rate limiting enzyme: phosphofructokinase or PFK. Prolonged exercise relies on third system i.e. the oxidative system. Kreb’s cycle: It is the continuation of the glycolysis chemical reaction. Depending on the presence or absence of the oxygen, the fate of pyruvic acid is determined, i.e. in the presence of oxygen, the pyruvic acid enters the Kreb’s cycle to yield further more energy, whereas in the absence of the oxygen, the pyruvic acid gets converted to lactic acid which further reduces to lactate. Carbohydrate dynamics in exercise: During anaerobic exercise carbohydrate become the sole fuel for ATP synthesis. Carbohydrate availability in the food consumed controls its supply to ATP formation during exercise. Concentration of blood glucose provides biofeedback regulation of the liver’s glucose output: an
  • 7. increase in blood glucose inhibits hepatic glucose release during exercise. Also, carbohydrate availability helps in fat mobilization and its use for energy. High intensity exercise:  Neural and hormonal factors during intense exercise increase the release of epinephrine, nor-epinephrine, and glucagon, where as decrease in insulin release. These hormonal responses activate glycogen phosphorylase which fascilitates glycogenolysis in the liver and muscle.  Muscle glycogen provides energy without oxygen during high intensity exercise training for 15-20min, later liver has to synthesize new glucose to fill in the exempted muscle glycogen and provides 40-50% of energy requirements, remaining is supplied by fat and protein catabolism.  An advantage of selective dependence on carb metabolism during intense aerobic exercise derives from its rate of energy transfer which is twice that of fat or protein. Moderate and prolonged exercise:  During low intensity exercise fat serves as the main energy substrate throughout exercise.  As submaximal exercise program increases progressively glycogen depletion is seen, and with time circulating fat increases and also their catabolism. Protein catabolism may also increase.  After certain amount of time, individual performing exercise gets exhausted and energy output decreases, this is when fat come into consideration. Fat oxidation provides energy in the later stage, the process being aerobic, is a slow process. *hitting the wall sensation: Effect of diet on muscle glycogen stores and endurance: Amount of storage of carbohydrate in muscle and liver=2500kcal to 2600kcal of energy. Lipids: Lipids ratio of hydrogen: oxygen exceeds that of carbohydrate, i.e. H:O=18.3:1. Approximately 98% of dietary lipids exists as triglycerol, while about 90% of the body’s total fat resides in the adipose tissue depots of the subcutaneous tissues. Types of lipids: Simple lipids Compound lipids Derived lipids a. Saturated fatty acids. b. Unsaturated fatty acids. c. Triacylglycerol a. High density b. Low density c. Very low density a. Simple lipids b. Compound lipids.
  • 8. d. Trans-fatty acids e. Lipids in diet. d. Chylomicrons Simple lipids/ neutral fats:  Consists primarily of triacylglycerol.  No affinity to water.  Major storage form of fat in adipocytes.  Synthesis of triacylglycerol molecules produces three molecules of water. Types: a. Saturated fatty acids: - Single covalent bonds between carbon atoms, and all of the remaining bonds attach to hydrogen. - Occur primarily in animal products such as beef, lamb, pork, chicken, egg yolk, dairy fats of cream, milk, butter and cheese. - Also found in plant kingdome in: coconut and plam oil, vegetable shortening, hydrogenated margarine, cakes, pies, cookies. b. Unsaturated fatty acids: - One or more double bonds along their main carbon chains. - Types: monounsaturated fatty acids (single double bond) and polyunsaturated fatty acids (more than one double bonds). - The chemical process of hydrogenation changes oils to semisolid fats by bubbling liquid hydrogen under pressure into vegetable oil. - Hydrogenated oils behave like saturated fat. c. Triacylglerol: i. Triacylglycerol formation: by a process termed as eterification. Occurs in adipocytes. Synthesis increases because of 2 main reasons, i). food absorption increases blood levels of fatty acids and glucose. ii). relatively high levels of circulating insulin fascilitates triacylglycerol synthesis. ii. Triacylglycerol breakdown: by a process termed as hydrolysis (to yield glycerol and energy rich fatty acid molecule.). Occurs in adipocytes. The mobilization of fatty acids via lipolysis predominates under four condition: - Low-to-moderate intensity exercise. - Low-calorie-dieting or fasting. - Cold stress. - Prolonged exercise that depletes glycogen reserves. d. Trans-fatty acid (unwanted fatty acid): generated by partial hydrogenation of unsaturated corn, soyabean, or sunflower oil. It forms when one of the hydrogen atom along the restricted chain moves from cis position to trans position, hence called so. e. Lipids in diet: avg US. consumes about 15% of total calories as saturated fatty acids. Health professional worrying about the affect of saturated fatty acids on human body, found out two course of action: - Replacing at least a portion of saturated fatty acids and all trans fatty acids by nonhydrogenated monounsaturated and polyunsaturated oils.
  • 9. - Balancing energy intake with regular physical activity to minimize weight gain and obtain the health benefits of regular exercise. - Consumption of more than 10% of total daily energy intake as saturated fatty acids is harmful. Compound lipids: Defnn of phospholipids. Glycolipids Lipoproteins Types of lipoproteins: a. High density: b. Low density: c. Very low density: d. Chylomicrons: FAT DYNAMICS DURING EXERCISE:  Intracellular and extracellular fats supply 30-80% of energy for physical activity depending on nutritional and fitness status and duration and intensity of exc. Exercise   Increased blood flow through adipocytes   Increases the release of FFA’s for delivery for use by muscle.  Long term consumption of high fat diet induces adaptation to the diet and hence utilization of fats as a source of energy during submaximal exc by fat oxidation process.  Usually fatty acids released provide energy in low-moderate intensity and greater duration exercise.  Aerobic training increases long-chain fatty acid oxidation during mild-to-moderate intensity exercise, primarily fatty acids from triglycerols within active muscles. Enhanced fat oxidation with training spares glycogen; this allows trained individuals to exercise at high levels of submaximal exercise before they experience fatigue.
  • 10. High fat diet Low fat diet Adaptation to this kind of diet shows shift in use towards higher fat oxidation during rest and exercise. Prolonged increase in intake of high fat diet Decreases FFA mobilization from adipocytes to the active muscle It becomes detrimental to health of athlete in future. By reducing carbohydrate and increasing fat to about 30% produces a more optimal zone for endurance performance. Restricting dietary fats below the RDA, can also impair exercise performance.