Energy Systems and Muscle Fibre Types

SECTION

5

• Energy is defined as the ability to do work.• Work is defined as the application of force

through a distance.• Six forms of energy:

1. light 4. nuclear2. heat 5. chemical3. electrical 6. mechanical

• Muscles convert CHEMICAL energy into MECHANICAL energy

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 of Energy currency Biochemical processes

The Three Energy Nutrients

Carbohydrates – glucose, glycogen

Proteins – amino acids

Fats – fatty acids

Metabolism refers to the process by which energy is supplied throughout the body. The chemical reactions will either require energy or release energy, the body’s metabolism may be thought of as a balancing act.

ANABOLIC – reactions that require energy to synthesize moleucles

CATABOLIC – reactions that release energy as they involve the breakdown of molecules

Adenosinetriphosphate (ATP)

ATP – is made in the mitochondrion

ATP is only an immediate source of energy for muscle contraction

Muscles have a small supply of ATP which satisfies the body’s initial needs, but is used quickly. Therefore, ATP must be re-synthesized.

ATP – is re-synthesized in two ways: aerobically and anaerobically

Aerobic and Anaerobic

Aerobic

– means in the presence of oxygen (02)

– all of its metabolic activity will involve 02

Anaerobic

– means without the use of oxygen (02)

– none of its metabolic activity will involve 02

ATP Cycle Overview

a) ATP breakdown

b) Phosphorylation

c) ATP resynthesis

1. Hydrolysis of the unstable phosphate groups of

ATP molecule by H2O

3. Energy is released (38-42 kJ, or 9-10kcal/ mol ATP)

ATP H2O++ 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 contractionMolecule 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

ATPADP Energy++ P++

3. Regeneration of ATP requires energy (from breakdown of food molecules)

c) ATP resynthesis

THREE ENERGY SYSTEMS FOR MUSCLES

• AEROBIC - burn sugar (glucose/glycogen) and fat, with oxygen

• ANAEROBIC - burn sugar without oxygen and get small energy AND LACTIC ACID

• CREATINE PHOSPHATE - allows muscle to replenish ATP quickly but not for long, continual durations

The Energy Systems

a) the high energy phosphagen system(anaerobic) ATP-PC System (anaerobic alactic)

b) the anaerobic glycolysis system Glycolysis (anaerobic lactic)

c) the aerobic system: cellular respiration

Three Metabolic PathwaysThree Metabolic Pathways

ATP-PC System(anaerobic alactic)

Glycolysis(anaerobic lactic)

Cellular respiration(aerobic)

High Energy Phosphate System

Muscle fibers have a unique molecule called creatine phosphate that can transfer its high energy

phosphate group to ADP thus forming ATP and creatine.

CreatineCreatinePP ENERGYENERGY

ADP + Pi ATPADP + Pi ATP

ATP-PC System Creatine phosphate is a high energy molecule where the phosphate can be broken off easily

and used to convert ADP to ATP Anaerobic alactic (without oxygen, no production of lactic acid) Uses stored ATP and creatine phosphate from within the muscle tissue. This supply is limited. No by-products

PC + ADP ATP + CREATINE

ATP-PC System (anaerobic alactic) First of two anaerobic energy

pathways Relies on the action of stored

ATP and phosphocreatine Yields enough ATP for 10–5

seconds of energy Provides highest rate of ATP

synthesis No by-product

ATP-PC SystemATP-PC System

The High Energy ATP - PC System OverviewAka: Phosphagen System

Primary energy source:

Duration of activity:

Sporting events:

Advantages:

Limiting factors:

Stored ATP, PC (phosphate creatine)

7-12 s

Power events such as: weight lifting, high jump, long jump, 100m run, 25m swim

Produce very large amount of energy in a short amount of time (very quick)

Initial concentration of high energy phosphates (ATP, PC) stored in muscles is minimal

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

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

GlycolysisGlycolysis

Glycolysis (anaerobic lactic) Second anaerobic energy

pathway Provides additional 1–3

minutes in high-level performance

Involves 11 separate biochemical reactions

Uses glucose and glycogen to make ATP

Yields twice as much ATP By product is lactic acid (LA)

C6H12O6 + 2ADP = 2Pi 2C3H6O3 + 2ATP + 2H2O(Glucose) (Lactate)

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

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

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

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

Aerobic Oxidative System

ADP + Pi ATPADP + Pi ATP

ENERGYENERGY

Carbon Dioxide

Carbon Dioxide WaterWater

GlycogenGlycogenO2O2

ProteinProtein

FatFat

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

Aerobic System

Only aerobic energy pathway Lasts 120 seconds and beyond Uses glucose, glycogen, fats, and proteins to make ATP By-products are carbon dioxide (CO2) and water (H2O)

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

Cori Cycle

• Lactic acid is taken to the liver to be metabolized back into pyruvic acid and then glucose

GlucoseGlucose

GlycogenGlycogen

LactateLactate

GlucoseGlucose

GlycogenGlycogen

LactateLactate

Blood Glucose

Blood Lactate

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 (CaO2)- depends on adequate ventilation and the O2-carrying

capacity of bloodb) 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-vO2 diff)- depends upon the rate of O2 diffusion from capillaries and the

rate of O2 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

The Roles of the Three Energy The Roles of the Three Energy Systems in Competitive Systems in Competitive

SportSport

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

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.