Energy for Muscular Activity

Learning Objectives:  To develop an awareness of the basic chemical process that 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

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 Carbohydrates Fats Proteins ATP Muscular Work Digesting Food Thermoregulation Breakdown ofEnergy currencyBiochemical processes

ATP Cycle Overview a) ATP breakdown b) Phosphorylation c) ATP resynthesis

1. Hydrolysis of the unstable phosphate groups of ATP molecule by H 2 O 3. Energy is released (38-42 kJ, or 9-10kcal/ mol ATP) ATP H2OH2O+Energy+P+ 2. Phosphate molecule (P) is released from ATP (ATP ADP) ADP a) ATP breakdown (ATP turnover)

1. Energy released by ATP turnover can be used by body when a free P group is transferred to another molecule (phosphorylation) Energy for muscle contraction Molecule P+ b) Phosphorylation

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 ATP ADP Energy+P+ 3. Regeneration of ATP requires energy (from breakdown of food molecules) c) ATP resynthesis

The Energy Systems a)the high energy phosphate system b) the anaerobic glycolytic system c) the aerobic oxidative system

The Roles of the Three Energy Systems in Competitive Sport

The High Energy Phosphate System Overview Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Stored ATP, CP 7-12 s Weight lifting, high jump, long jump, 100m run, 25m swim Produce very large amount of energy in a short amount of time Initial concentration of high energy phosphates (ATP, PC)

High Energy Phosphate System

Training the High Energy Phosphate System a) Interval training: - 20% increase in CP (creatine phosphate) stores - no change in ATP stores - increase in ATPase function (ATP -> ADP+P) - 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% - 100% increase in resting ATP stores

The Anaerobic Glycolytic System Overview Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Stored glycogen, blood glucose 12 s – 3 min Lactic acid build up, H+ ions build up (decrease of pH) 800m run, 200m swim, downhill ski racing, 1500 speed skating Ability to produce energy under conditions of inadequate oxygen

The Anaerobic Glycolytic System

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

The highly complex metabolic pathways of glycolysis )

Anaerobic Threshold  The exercise intensity at which lactic acid begins to accumulate within the blood  The point during exercise where the person begins to feel discomfort and burning sensations in their muscles  Lactic acid is used to store pyruvate and hydrogen ions until they can be processed by the aerobic system

The Anaerobic Glycolytic System cont.  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

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

Glucose stored in blood Glycogen stored in muscle or liver Complex Carbohydrates Digestive system Glycogen Gluconeogenesis Circulation of glucose around body Glucose Blood Stream Carbohydrate breakdown and storage

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 in non-working muscle

Primary energy source: Duration of activity: Sporting events: Advantages: Limiting factors: Glycogen, glucose, fats, proteins > 3 min Lung function, max.blood flow, oxygen availability, excess. energy demands Walking, jogging, swimming, walking up stairs Large output of energy over a long period of time, removal of lactic acid The Aerobic Oxidative System Overview

Aerobic Oxidative System

The Aerobic Oxidative System  The most important energy system in the human body  Blood lactate levels remain relatively low (3-6mmol/L bl)  Primary source of energy (70-95%) 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

The Oxidative Phosphorylation System  Two Pathways: Krebs Cycle & Electron Transport Chain  Biochemical process used to resynthesize ATP by combining ADP and P 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

Cori Cycle  Lactic acid is taken to the liver to be metabolized back into pyruvic acid and then glucose

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 VO2 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-vO 2 diff) - depends upon the rate of O 2 diffusion from capillaries and the rate of O 2 utilization

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, protect the body from cold, and serve to transport vitamins each gram of fat contains 9 calories of energy

Effect 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 the muscle fibres - increases the activity of enzymes (Krebs cycle) - preferential use of fats over glycogen during exercise  Endurance training increases the max aerobic power of a sedentary individual by 15-25% regardless of age  An older individual adapts more slowly

Summary of the three energy systems

The Role of Three Energy Systems During an All-out Exercise Activity of Different Duration

Factors Affecting Physical Performance

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.