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Biochemistry of
Professor Dr. Najat A. Hasan
(MB ChB, MSc, PhD in Clinical
Biochemistry, College of
Medicine -Alnahrain University,
Baghdad. Iraq)
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
-SPORT is a Physical activity where
skeletal muscles
contraction result in an increase in energy expenditure.
Principles of Training or Sports
• Overload
– occurs when a system is exercised at a level beyond
which it is normally accustomed
• Specificity
– Training is specific to the muscle fibers involved
– Type of exercise
• Reversibility
– Gains are lost when overload is removed
Different Methods of sports training
There are many types of sports training methods practiced
through-out the world. Three of the main types:
– Weight Training: Increases strength . focus on totally
different parts of the body: Chest, shoulders, back, arms,
legs and even neck .
– Speed Training: Speed training is influenced by :
- Strength
– Flexibility training: All pro athletes start and finish
training sessions by doing flexibility exercises.
– Not only helps out in performance, but it also helps lower
back pain.
- Stretching increases tissue temperature, blood supply, nutrient
transport to tissue and synovial fluid.
The energy sources of physical activity is dependent on:
1. Intensity of the physical activity
2. The duration of physical activity
3. Personal characteristics
The combination of characteristics of physical activity (intensity ,
duration) ,genetic features, fitness will determine the ratio
between various energy production pathways utilized by the
Energy systems
1. the high energy phosphate system (ATP-CP System)
2. the anaerobic glycolytic system (Lactic Acid System)
3. the aerobic oxidative system (Oxygen System)
1. The High Energy Phosphate System
Primary energy source:
ATP( 2-3 s) , Stored ATP, CP
Duration of activity:
7-12 s
Sporting events:
Weight lifting, high jump, long jump, 100m run,
25m swim
Produce very large amount of energy in a
short amount of time
Limiting factors:
Initial concentration of high energy phosphates
- The usefulness isn’t the AMOUNT of Energy but the QUICK & POWERFUL
- For longer periods of work = The Aerobic & Anaerobic Energy System must be
Training: the High Energy Phosphate System
a) Interval training:
- 20% increase in creatine phosphate(CP ) stores
- no change in ATP stores
- increase in ATPase function (ATP -> ADP+P)
- increase in creatine phosphokinase (CPK) function
.CPK breaks down CP molecule and allows ATP
b) Sprint training:
- increase in CP stores up to 40%
- 100% increase in resting ATP stores
2. 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
Ability to produce energy under conditions of
inadequate oxygen
Limiting factors:
Lactic acid build up, H+ ions build up
(decrease of pH)
• Starts when:
– the reserves of high energy phosphate compounds fall to a low
– the rate of glycolysis is high and there is a buildup of pyruvic
Hydrolysis of Glucose: 2 molecules of ATP + 2 molecules of pyruvic acid
Hydrolysis of Glycogen : 3 molecules of ATP + 2 molecules of Lactic acid
The highly complex
metabolic pathways of
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
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 …cori cycle
3. 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
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
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
The Oxidative Phosphorylation System
• Two Pathways: Krebs Cycle & Electron Transport Chain
• There is resynthesis of 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 129 ATP molecules
By-products of this reaction: carbon dioxide, water
O2 enters the system, stopping the breakdown of glycogen to lactic
acid , glycogen breaks down into: ATP + CO2 + H20
These byproducts are easier to get rid of :CO2 is expelled by the lungs
H2O is used in the muscle
The Substrates for the Aerobic System
Carbohydrates& fat
 With prolonged exercise, Carbohydrates are the first fuel
choice, as exercise continues, Fat becomes predominant
 Protein is not a main fuel source except in an
direct muscle oxidation (branched chain amino acids)
gluconeogenesis in liver from amino acids
Proteins provide low rate of ATP-energy production
Limited total energy capacity
Is considered significant source of energy during long
endurance events
Factors Affecting Physical
Somatic Factors Nature of the Work Psychic Factors
Environmental Factors
Body distribution Technique (efficiency)
Air pressure (hypobaric and hyperbaric)
State of health
Body position
Air pollution
Fibre type distibution Work:rest schedule
Muscle Fiber Types: A determinant of sport
Muscle fibers have been identified as red or white fibers,
where red fibers were suited to long-term slow muscle
contractions .White fibers were suited to high-speed
contractions. The three major muscle fiber types seen in
human skeletal muscle:Slow oxidative fiber (I, aerobic), called slow-twitch oxidative
Fast glycolytic fibers(II a, mixed)
Fast oxidative glycolytic(II b, anaerobic)
 The metabolic and contractile properties of these fibers
can influence exercise performance.
Slow-twitch fibers are fatigue-resistant and thus suited to longerterm, aerobic activities. They have greater myoglobin and mitochondria
levels than fast twitch fibers, and are thus reliant upon aerobic metabolism
to function. They contract at a much slower speed than fast-twitch fibers
and have a low glycolytic capacity. The major differences between the
fiber types are displayed in Table 1.
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 fibers
- 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 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
• 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
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-vO2 diffusion)
- depends upon the rate of O2 diffusion from capillaries and the
rate of O2 utilization
•When the muscle does not get enough oxygen, exhaustion is
reached causing immediate and involuntary reduction in intensity
VO2max is Product of maximal cardiac output (Q) and arteriovenous difference
(a-vO2) :
VO2max = HRmax x SVmax x (a-vO2)max, SV is the stroke volume.
Factors Increasing Stroke Volume (SV )
 Increased SVmax
 Preload (End Diastolic volume)
•  Plasma volume
•  Venous return
•  Ventricular volume
 Afterload (Total peripheral
•  Arterial constriction
•  Maximal muscle blood flow
with no change in mean arterial
 Contractility
a-vO2 Difference and Increased
Improved ability of the muscle to extract oxygen
from the blood
 Muscle blood flow
  Capillary density
  Mitochondrial number
Increased a-vO2 difference accounts for 50% of
increased VO2max
arterio-venous difference in O2 (a-vO2)
Structural and Biochemical
Adaptations to Endurance
 Mitochondrial number
 Oxidative enzymes: Krebs cycle (citrate
 Fatty acid (-oxidation)
 Electron transport chain
 NADH shuttling system
Change in type of LDH
Adaptations quickly lost
with detraining
in Mitochondria
About 50% of the increase
in mitochondrial content
was lost after one week of
All of the adaptations were
lost after five weeks of
It took four weeks of
retraining to regain the
adaptations lost in the first
week of detraining
Effect Intensity and Duration on
Mitochondrial Enzymes
Citrate synthase (CS)
Marker of mitochondrial oxidative capacity
 Light to moderate exercise training
• Increased CS in high oxidative fibers
(Type I and IIa)
Strenuous exercise training
• Increased CS in low oxidative fibers
(Type IIb)
Biochemical Changes
and FFA Oxidation
Increased mitochondrial
number and capillary density
 Increased capacity to
transport FFA from plasma
to cytoplasm to
Increased enzymes of oxidation
 Increased rate of acetyl CoA
Increased FFA oxidation
 Spares muscle glycogen and
blood glucose
FFA Oxidation and
Mitochondrial and
Biochemical Adaptations
and Blood pH
Blood Lactate
Balance between lactate
production and removal
Lactate production during
exercise depend on: NADH,
pyruvate, and LDH in the
Blood pH affected by blood
lactate concentration
pyruvate + NADH
lactate + NAD
Benefits of running/jogging/exercise
Reduction in premature deaths
Lowers risk of developing high BP
Reduces risk of developing colon & breast
Reduces risk of developing diabetes
Reduces or maintains body weight/fat
Builds and maintains healthy muscles bones and
tissue perfusion.
Enhance physical, sport performance
Improves psychological well-being, reduces
depression, anxiety,
Sweat losses vary between athletes but increase with temperature,
intensity & duration of exercise …(3.7 L/hr)
Physiological responses to dehydration:
 1%: thirst
 2%: decreased sweat rate, cardiac output, VO2, muscle strength
and liver glycogen, therefore, decreased performance
 5%: discomfort, alternating states of lethargy and nervousness,
irritability, fatigue, loss of appetite
 7%: Extreme danger; salivating & swallowing becomes difficult
Before Exercise: Pre-cooling improves endurance performance (cool
shower/bath/vests). 500mL every 2 – 3hrs prior to exercise (water,
juice, milk, cordial, sports drink) and 5ml/kg immediately before
During: 250mL every 15-20min OR as much is comfortable during
exercise (water, sports drink)
After: 150% of fluid deficit;
Aim for 500mL to 1000mL (sports drinks, as the electrolytes help
stimulate the thirst drive)