Energy for Muscular Activity Chapter 7 Sport Books Publisher 1 Learning Objectives: To develop an awareness of the basic chemical processes the body uses to produce energy in the muscles To develop an understanding of the body s three main energy systems To introduce the effect of training and exercise on the energy systems Sport Books Publisher 2 The Chemistry of Energy Production Energy in the human body is derived from the breakdown of complex nutrients like carbohydrates, fats, and proteins The end result of this breakdown is production of the adenosine triphosphate (ATP) molecule ATP provides energy necessary for body functions Breakdown of Energy currency Biochemical processes Carbohydrates Fats Proteins ATP Muscular Work Thermoregulation Digesting Food Sport Books Publisher 3
ATP Cycle Overview a) ATP breakdown b) Phosphorylation c) ATP resynthesis Sport Books Publisher 4 a) ATP breakdown (ATP turnover) ATP + H 2 O ADP + Energy + P i 1. Hydrolysis of the unstable phosphate groups of ATP molecule by H 2 O 2. Phosphate molecule (P i ) is released from ATP (ATP ADP) 3. Energy is released (38 to 42 kj, or 9 to 10 kcal/mol ATP) Sport Books Publisher 5 b) Phosphorylation Molecule + P i Energy for muscle contraction 1. Energy released by ATP turnover can be used by body when a free P i group is transferred to another molecule (phosphorylation) Sport Books Publisher 6
c) ATP resynthesis ADP + Energy + P i ATP 1. Initial stores of ATP in the muscles are used up very quickly and ATP must be regenerated 2. ATP is formed by recombination of ADP and P i 3. Regeneration of ATP requires energy (from breakdown of food molecules) Sport Books Publisher 7 The Energy Systems a) High energy phosphate system b) Anaerobic glycolytic system c) Aerobic oxidative system Sport Books Publisher 8 The Roles of the Three Energy Systems in Competitive Sport Sport Books Publisher 9
Sport Books Publisher 10 High Energy Phosphate System Overview Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Stored ATP, CP 7 to 12 s Weightlifting, high jump, long jump, 100 m run, 25 m swim Produces very large amount of energy in a short amount of time Initial concentration of high energy phosphates (ATP, PC) Sport Books Publisher 11 High Energy Phosphate System PP ENERGY Creatine ADP + P ii ATP Sport Books Publisher 12
Training the High Energy Phosphate System a) Interval training: - 20 percent increase in CP (creatine phosphate) stores - no change in ATP stores - increase in ATPase function (ATP ADP + P i ) - increase in CPK (creatine phosphokinase) function (CPK breaks down CP molecule and allows ATP resynthesis) b) Sprint training: - increase in CP stores up to 40 percent - 100 percent increase in resting ATP stores Sport Books Publisher 13 The Anaerobic Glycolytic System Overview Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Stored glycogen, blood glucose 12 s to 3 min 800 m run, 200 m swim, downhill ski racing, 1500 m speedskating Ability to produce energy under conditions of inadequate oxygen Lactic acid build up, H+ ions build up (decrease of ph) Sport Books Publisher 15
The Anaerobic Glycolytic System ENERGY Glycogen Lactic Lactic Acid Acid ADP + P ii ATP Sport Books Publisher 16 Glycolysis A biochemical process that releases energy in the form of ATP from glycogen and glucose anaerobic process (in the absence of oxygen) The products of glycolysis (per molecule of glycogen): - 2 molecules of ATP - 2 molecules of pyruvic acid The by-product of glycolysis (per molecule of glycogen): - 2 molecules of lactic acid Sport Books Publisher 17 The highly complex metabolic pathways of glycolysis ) Sport Books Publisher 18
Anaerobic Threshold The exercise intensity at which lactic acid begins to accumulate within the blood The point during exercise where a person begins to feel discomfort and burning sensations in the muscles Lactic acid is used to store pyruvate and hydrogen ions until they can be processed by the aerobic system Sport Books Publisher 19 The Anaerobic Glycolytic System Starts when: the reserves of high energy phosphate compounds fall to a low level the rate of glycolysis is high and there is a buildup of pyruvic acid Sport Books Publisher 20 Substrates for the anaerobic energy system The primary source of substrates is carbohydrate Carbohydrates: primary dietary source of glucose primary energy fuels for brain, muscles, heart, liver Sport Books Publisher 21
Carbohydrate breakdown and storage Complex Carbohydrates Digestive system Glucose Blood Stream Circulation of glucose throughout body Glucose stored in blood Glucogenesis Glycogen Glycogen stored in muscle or liver Sport Books Publisher 22 Effect of Training on the Anaerobic Glycolytic System Rate of lactic acid accumulation is increased in the trained individual This rate can be decreased by: a) reducing the rate of lactate production - Increase in the effectiveness of the aerobic oxidative system b) increasing the rate of lactate elimination - Increased rate of lactic acid diffusion from active muscles - Increased muscle blood flow - Increased ability to metabolize lactate in the heart, liver, and non-working muscles Sport Books Publisher 23
The Aerobic Oxidative System Overview Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Glycogen, glucose, fats, proteins > 3 min Walking, jogging, swimming, walking up stairs Large output of energy over a long period of time, removal of lactic acid Lung function, max blood flow, oxygen availability, excessive energy demands Sport Books Publisher 25 Aerobic Oxidative System O 2 ENERGY Glycogen Fat Protein ADP + P ii ATP Carbon Dioxide Water Sport Books Publisher 26 The Aerobic Oxidative System The most important energy system in the human body Blood lactate levels remain relatively low (3 to 6 mmol/l blood) Primary source of energy (70 to 95 percent) for exercise lasting longer than 10 minutes provided that: a) working muscles have sufficient mitochondria to meet energy requirements b) sufficient oxygen is supplied to the mitochondria c) enzymes or intermediate products do not limit the Kreb s cycle Primary source of energy for the exercise that is performed at an intensity lower than that of the anaerobic oxidative system Sport Books Publisher 27
The Oxidative Phosphorylation System Two Pathways: Kreb s Cycle and Electron Transport Chain Biochemical process used to resynthesize ATP by combining ADP and P i in the presence of oxygen Takes place in mitochondrion (contains enzymes, co-enzymes) Energy yield from 1 molecule of glucose is 36 ATP molecules Energy yield from 1 molecule of fat up to 169 ATP molecules By-products of this reaction: carbon dioxide, water Sport Books Publisher 28 Cori Cycle Lactic acid is taken to the liver to be metabolized back into pyruvic acid and then glucose Blood Glucose Glucose Glycogen Lactate Blood Lactate Glucose Glycogen Lactate Sport Books Publisher 29 The Power Of The Aerobic System Evaluated by measuring the maximal volume of oxygen that can be consumed per kilogram of mass in a given amount of time This measure is called aerobic power or VO 2 max (ml/min/kg) Factors that contribute to a high aerobic power: a) Arterial oxygen content (CaO 2 ) - Depends on adequate ventilation and the O 2 -carrying capacity of blood b) Cardiac output (Q = HR x stroke volume) - Increased by elevation of the work of heart and increased peripheral blood flow c) Tissue oxygen extraction (a-v O 2 difference) - Depends upon the rate of O 2 diffusion from capillaries and the rate of O 2 utilization Sport Books Publisher 30
The Substrates for the Aerobic System Carbohydrates (glycogen and glucose) and fats (triglycerides and fatty acids) Fats: found in dairy products, meats, table fats, nuts, and some vegetables body s largest store of energy, cushion the vital organs, insulate the body from cold, and serve to transport vitamins each gram of fat contains 9 kilocalories of energy Sport Books Publisher 31 Effects of Training on Aerobic Systems Endurance training is the most effective method (long duration several times per week): - increases vascularization within muscles - increases number and size of mitochondria within muscle fibers - increases the activity of enzymes (Kreb s cycle) - preferential use of fats over glycogen during exercise Endurance training increases the max aerobic power of a sedentary individual by 15 to 25 percent regardless of age An older individual adapts more slowly Sport Books Publisher 32 Summary of the three energy systems Characteristic High energy phosphate Anaerobic glycolytic Aerobic oxidative Other names phosphagen, ATP/CP lactic acid steady state Fuel source(s) stored ATP, PC stored glycogen, blood glycogen, glucose, fats, glucose proteins Enzyme sytem used in single enzyme single enzyme multiple enzymes breakdown Muscle fibre type(s) recruited SO, FOG, FG SO, FOG, FG depends on level of effort Power output requirement high high low Metbolic byproducts ADP, P, C lactic acid CO2, H2O maximum rate of ATP 3.6 1.6 1 production (mmol/min) Time to maximal ATP 1 sec 5-10 sec 2-3 min production Maintenance time of maximal 6-10 sec 20-30 sec 3 min ATP production Time to exhaustion of system 10 sec 3040 sec 5-6 min ATP production capacity (mol) 0.6 1.2 theoretically unlimited Relative % ATP contribution to 50 35 15 efforts of 10 sec Relative % ATP contribution to 15 65 20 efforts of 30 sec Relative % ATP contribution to 4 46 50 efforts of 2 min Relative % ATP contribution to 1 9 90 efforts of 10 min Time for total recovery (sec) 3 min 1-2 hr 30-60 min Time for one half recovery 20-30 sec 15-20 min 5-10 min (sec) Ultimate limiting factor(s) Depletion of ATP / creatine Lactic acid accumulation Depletion of carbohydrate phosphate stores resulting from production stores, insufficient oxygen, exceeding buffer capacity. heat accumulation Sport Books Publisher 33
The Role of Three Energy Systems During an All-out Exercise Activity of Different Duration Sport Books Publisher 34 Factors Affecting Physical Performance Somatic Factors Nature of the Work Psychic Factors Environmental Factors Sex Intensity Attitude Diet Age Duration Motivation Temperature Body distribution Technique (efficiency) Air pressure (hypobaric and hyperbaric) State of health Body position Air pollution Drugs Mode Noise Strength Type Fibre type distibution Work:rest schedule Sport Books Publisher 35 Discussion Questions: 1. What are the differences between the 3 energy systems? 2. List one advantage and one disadvantage of each of the 3 energy systems. 3. Give an example of three activities or sports that use each of (a) the high energy phosphate system, (b) the anaerobic glycolytic system, and (c) the aerobic oxidative system as their primary source of energy (one sport for each energy system). 4. What is the most important source of fuel in the body for all types of energy production a substance also known as the energy currency of the body? 5. Define ATP turnover and ATP resynthesis. 6. Describe how each of the three energy systems could be trained most efficiently. Sport Books Publisher 36