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
Breakdown of
Energy currency
Carbohydrates
Fats
Proteins
Biochemical processes
Muscular Work
ATP
Thermoregulation
Digesting Food
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)
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:
Stored ATP, CP
Duration of activity:
7-12 s
Sporting events:
Weight lifting, high jump, long jump,
100m run, 25m swim
Advantages:
Produce very large amount of energy in
a short amount of time
Limiting factors:
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:
Stored glycogen, blood glucose
Duration of activity:
12 s – 3 min
Sporting events:
800m run, 200m swim, downhill ski
racing, 1500 speed skating
Advantages:
Ability to produce energy under
conditions of inadequate oxygen
Limiting factors:
Lactic acid build up, H+ ions build
up (decrease of pH)
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
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
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
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
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 (CaO2)
- depends on adequate ventilation and the O2-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
O2
c) tissue oxygen extraction (a-vO2 diff)
- depends upon the rate of O2 diffusion from capillaries and the rate of
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
Characteristic
Other names
Fuel source(s)
High energy phosphate
phosphagen, ATP/CP
stored ATP, PC
Enzyme sytem used in
breakdown
Muscle fibre type(s) recruited
Power output requirement
Metbolic byproducts
maximum rate of ATP
production (mmol/min)
Time to maximal ATP
production
Maintenance time of maximal
ATP production
Time to exhaustion of system
ATP production capacity (mol)
single enzyme
Anaerobic glycolytic
lactic acid
stored glycogen, blood
glucose
single enzyme
Aerobic oxidative
steady state
glycogen, glucose, fats,
proteins
multiple enzymes
SO, FOG, FG
high
ADP, P, C
3.6
SO, FOG, FG
high
lactic acid
1.6
depends on level of effort
low
CO2, H2O
1
1 sec
5-10 sec
2-3 min
6-10 sec
20-30 sec
3 min
10 sec
0.6
3040 sec
1.2
5-6 min
theoretically unlimited
Relative % ATP contribution to
efforts of 10 sec
Relative % ATP contribution to
efforts of 30 sec
Relative % ATP contribution to
efforts of 2 min
Relative % ATP contribution to
efforts of 10 min
Time for total recovery (sec)
Time for one half recovery
(sec)
Ultimate limiting factor(s)
50
35
15
15
65
20
4
46
50
1
9
90
3 min
20-30 sec
1-2 hr
15-20 min
30-60 min
5-10 min
Depletion of ATP / creatine
phosphate stores
Lactic acid accumulation
resulting from production
exceeding buffer capacity.
Depletion of carbohydrate
stores, insufficient oxygen,
heat accumulation
The Role of Three Energy Systems During an All-out
Exercise Activity of Different Duration
Factors Affecting Physical Performance
Somatic Factors
Sex
Age
Body distribution
State of health
Drugs
Strength
Fibre type distibution
Nature of the Work
Intensity
Duration
Technique (efficiency)
Body position
Mode
Type
Work:rest schedule
Psychic Factors
Attitude
Motivation
Environmental Factors
Diet
Temperature
Air pressure (hypobaric and hyperbaric)
Air pollution
Noise
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.