Download Energy Systems and Muscle Fibre Types

5
SECTION
Energy Systems and Muscle
Fibre Types
• 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. nuclear
2. heat
5. chemical
3. 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
Breakdown of
Energy currency
Carbohydrates
Fats
Proteins
Biochemical processes
Muscular Work
ATP
Thermoregulation
Digesting Food
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 resynthesized.
 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
a) ATP breakdown (ATP turnover)
ATP
+ H 2O
ADP
+ Energy + P
1. Hydrolysis of the unstable phosphate groups of
ATP molecule by H2O
2. Phosphate molecule (P) is released from ATP
(ATP
ADP)
3. Energy is released (38-42 kJ, or 9-10kcal/ mol ATP)
b) Phosphorylation
Molecule + P
Energy for muscle contraction
1. Energy released by ATP turnover can be used by body
when a free P group is transferred to another molecule
(phosphorylation)
c) ATP resynthesis
ADP
+ Energy + P
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
3. Regeneration of ATP requires energy (from
breakdown of food molecules)
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 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.
P
ENERGY
Creatine
ADP + 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
ATP-PC System
 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
PC + ADP
ATP + CREATINE
The High Energy ATP - PC System Overview
Aka: Phosphagen System
Primary energy source:
Stored ATP, PC (phosphate creatine)
Duration of activity:
7-12 s
Sporting events:
Power events such as: weight lifting, high
jump, long jump, 100m run, 25m swim
Advantages:
Produce very large amount of energy in
a short amount of time (very quick)
Limiting factors:
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
Glycolysis
 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
(Glucose)
2C3H6O3 + 2ATP + 2H2O
(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
.
Carbohydrate breakdown and storage
Complex
Carbohydrates
Digestive
system
Glucose
Blood
Stream
Circulation of glucose
around body
Glucose stored
in blood
Gluconeogenesis
Glycogen
Glycogen stored
in muscle or liver
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
O2
Glycogen
Fat
ENERGY
Protein
ADP + Pi  ATP
Carbon
Dioxide
Water
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)
The Aerobic Oxidative System Overview
Primary energy source:
Glycogen, glucose, fats, proteins
Duration of activity:
> 3 min
Sporting events:
Walking, jogging, swimming,
walking up stairs
Advantages:
Large output of energy over a long
period of time, removal of lactic acid
Limiting factors:
Lung function, max.blood flow, oxygen
availability, excess. energy demands
Cori Cycle
• Lactic acid is taken to the liver to be
metabolized back into pyruvic acid and then
glucose
Glucose
Lactate
Blood
Glucose
Glycogen
Blood
Lactate
Glucose
Lactate
Glycogen
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)
blood
- depends on adequate ventilation and the O2-carrying capacity of
b) cardiac output (Q = HR x stroke volume)
- increased by elevation of the work of heart and increased
peripheral
rate of O2
blood flow
c) tissue oxygen extraction (a-vO2 diff)
- depends upon the rate of O2 diffusion from capillaries and the
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
Systems in Competitive Sport
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.