Bioenergetics and Performance

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Bioenergetics and Performance
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Equine Exercise Physiology

• Superior athletic performance is multifaceted.
• And is the result of integration of the major
  body systems involved in delivering energy, as
  well as biomechanical factors.

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Major physiological factors contributing to
superior performance
Hemoglobin concentration
Gas exchange
Biomechanics
Athletic performance
Anaerobic capacity
Heart size
Skeletal muscle properties
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Equine Exercise Physiology
O2 in air
O2 transport via conducting airways

• Aerobic energy delivery
• function of heart rate
• stroke volume
• oxygen extraction by muscle
• Is the result of a complex chain of events
  involving the O2 transport chain.

O2 diffusion across alveolar capillary interface
O2 binding to hemoglobin
O2 distribution via the circulation
O2 utilization by mitochondria
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Equine Exercise Physiology

• Anaerobic energy delivery
• is more direct and predominates in the rapid
  delivery of energy for brief periods of intense
  exercise.

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Muscle glycogenconcentration
Important factors contributing to anaerobic
capacity
of Type II fibers
Muscle buffering capacity
Anaerobic capacity
Rate of Glycogenolysis
Muscle fiber area
Muscle concentration of high energy P
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Equine Exercise Physiology

• Will to Win
• Its almost impossible to define what contributes
  to that elusive distinguish of the champion horse
  within an elite group.

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Equine Exercise Physiology

• Energetics of exercise
• For performance horses, one of the most important
  considerations is how the horse obtains its
  energy from the diet it is fed.
• The horse is like a high performance race car.
• Most horses are fed a combination of forage and
  cereal grains

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Equine Exercise Physiology

• Certain amount of fuel must be provided w/in the
  diet to support the horses energy requirement.
• 1 to 2 hrs after a meal
• Specially a cereal grain meal
• Blood glucose levels rise
• 5 millimoles/liter to 7 mmole/L of blood
• Insulin response
• Ensures that muscle and liver has sufficient fuel
  stores.

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Equine Exercise Physiology

• Liver function
• Aided by a number of hormones
• Acts as a glucostat regulator of glucose
• Ensures the homeostasis of blood glucose
• Guaranteeing a constant supply of glucose to the
  brain and heart

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Energy Production

• Energy cannot be created or destroyed
• it can only be converted from one form into the
  another.
• All animals convert chemical energy from food
  into mechanical energy of work and heat is given
  off as a by-product.

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Energy Production

• Adenosine triphosphate (ATP) is the universal
  fuel source.
• ATP provides a chemical energy that can be used
  by all cells, in all animals.
• All pathways are designed to produce adenosine
  triphosphate (ATP), which is the ultimate
  substrate utilized by muscle.
• ATP has a high-energy phosphate bond which, when
  cleaved, produces the energy required for
  muscular contraction and relaxation.
• Adenosine triphosphatase (ATPase)

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Energy Production
An active horse may actually turn over 4xs their
own bodyweight in ATP per day.
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Energy Production

• The continuous supply of ATP to contracting
  muscle is reliant on the integrative function of
  many body systems including
• gastrointestinal tract
• cardiovascular
• respiratory
• musculoskeletal systems

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Energy Production

• The main fuels used to provide energy
• Glucose (CHO)
• Glycogen (CHO)
• Fatty acids (fats)
• Protein
• Only used to provide energy in cases
• Extreme exhaustion
• Starvation
• Disease

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Sources of Energy

• Carbohydrates - are stored w/in liver, muscle,
  and adipose tissue.
• Glucose is stored principally as glycogen in the
  muscle and liver,
• One glucose molecule can yield up to 38 ATP
  molecules.

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Sources of Energy

• During short bouts of high-intensity exercise,
  muscle glycogen concentrations have been shown
  to decrease by approx. 20 -30.
• Therefore, its unlikely that glycogen
  availability limits this type of performance.

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Sources of Energy

• Prolonged exercise results in the greatest
  depletion of muscle glycogen.
• Snow et al., 1981
• In endurance horses competing in an 80 - km ride
  (50 miles), the muscle mean glycogen
  concentration fell by 56.

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Sources of Energy

• Fats - Lipids are stored w/in the muscle as well
  as in extramuscular depots as adipose tissue.
• Withers, crest, loins, and around internal organs
• This is where triglycerides undergo hydrolysis to
  glycerol and free fatty acids (FFAs).
• One mole of stearic acid (285 g), when oxidized,
  yields approx. 146 mol ATP.
• Thus, 69 of the energy is for ATP production,
  with the remaining 31 lost as heat.

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Sources of Energy

• During low-intensity exercise, fat has been shown
  to be a major energy source.
• High-fat diets have been shown to have a
  paradoxical effect on glycogen stores.
• Horse fed a fat-supplemented diet increased
  resting muscle glycogen concentration by 18 to 52
  .
• Vegetable oils are the most readily available
  sources of fat that can be used as a dietary
  supplement.

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Energy Production

• There are several biochemical routes for
  phosphorylation of ADP.
• Energy Pathways
• Pathways will be automatically selected w/in any
  particular period of exercise.
• Pathways are not used on an all or nothing basis
• Many pathways may be used simultaneously for
  generating energy

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Energy Pathways
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Energy Pathways
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Energy Pathways
Energy-yielding nutrients CHO Fats Proteins
Cell macromolecules Proteins Polysaccharides Lipid
s Nucleic acids
ADP HPO42- NAP NADP
Anabolism
Catabolism
ATP NADH NADPH
Precursor molecules Amino Acids Sugars Fatty
Acids Nitrogenous base
Energy-poor end prod. CO2 H2O NH3
Chemical Energy
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Energy Production

• The horse will select a particular combination of
  energy pathways.
• Depends on
• Nature of the exercise
• The state of its fuel stores
• There are four basic energy pathways
• Two require oxygen (aerobic energy pathways)
• Two that do not require oxygen (anaerobic energy
  pathways)

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Energy Production

• In aerobic reactions, oxygen is the final
  electron acceptor.
• In anaerobic reactions, glucose and glycogen can
  be split into two or more parts, and one of these
  parts can be oxidized by another.

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Energy Production
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Energy Pathway 1

• Anaerobic phosphorylation of ADP using high
  energy phosphate stores in muscle.
• High energy phosphates include molecules such as
  phosphocreatine (PCr)
• Energy is bound up in their structure
• Catalysed by creatine phophokinase (CK or CPK)
• PCr ADP ? Cr ATP
• Myokinase reaction
• ADP ADP ? AMP ATP
• Usually under high intensity exercise
• Recruits those muscle fiber also

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Energy Pathway 1

• These rxn can be self-limiting.
• Build up of AMP
• To remove AMP an enzyme is needed.
• AMP deaminase
• Converts AMP to inosine monophosphate (IMP) and
  ammonia.
• The stores of ATP and PCr are small
• Can only maintain exercise for a mere few seconds

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Energy Pathway 1

• Once other forms of energy production has taken
  over
• High energy phosphate stores can be replenished
• If exercise is of low to medium intensity
• During high intensity
• Muscle ATP and PCr concentrations may be reduced
  by 50 70
• As a result of decreases in muscle pH consequent
  to Lactic acid production.

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Energy Pathway 2

• Aerobic (oxidative) phosphorylation of ADP using
  carbohydrate stores.
• Breakdown of glycogen w/in muscle using oxygen
  involves several stages.
• First stage
• Conversion of glycogen to pyruvate
• Occurs in the cytoplasm of the cell
• Without the involvement of oxygen

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Energy Pathway 2
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Energy Pathway 2
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Energy Pathway 2

• Conversion of glycogen to Glucose
• Know as glycogenolysis
• Involves a specific phosphorylating reaction
• Results in the formation of glucose-1-phosphate
• Controlled by an enzyme called glycogen
  phosphorylase
• Both active and inactive
• Termed a and b
• After conversion Glu-1-P
• to Glu-6-P it can enter the
• glycolytic pathway

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Energy Pathway 2
Glycogen Phosphorylase
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Energy Pathway 2

• Glycolysis conversion of glucose to pyruvate
• Takes place rapidly
• Yields small amount of ATP
• Produces 2 molecules of pyruvate
• All rxn take place in cytoplasm of cell
• Regulated by the enzyme Hexokinase
• Requires the consumption of 1 ATP

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Energy Pathway 2
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Energy Pathway 2

• The next stage
• Pyruvate is converted to Acetyl CoA
• Occurs only in the mitochondria
• Catalyzed by an enzyme called pyruvate
  dehydrogenase (PDH)

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Energy Pathway 2

• Third stage
• Acetyl CoA initiates a series of rxn know as the
  tricarboxylic acid (TCA) cycle
• Also referred to as the Krebs cycle
• Net production of 2 ATP and 2 H ions
• H ions combine w/
• nicotinamide adenine dinucleotide (NAD)
• Flavin adenine dinucleotide (FAD)
• Produce
• NADH and FADH2
• Products enter electron transport chain

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Energy Pathway 2
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Energy Pathway 2

• Hydrogen ions are split into electrons and
  protons
• ADP is regenerated to yield 34 molecules of ATP
• The H ions combine with oxygen to produce water.
• This process requires oxygen so
• Termed
• Aerobic
• Oxidative phosphorylation

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Energy Pathway 2

• Oxidation-reduction reactions
• Oxidation - is the loss of electrons from an atom
  or molecule.
• Reduction - is the acceptance of electrons.
• Hydrogen atoms - are the principle carriers of
  electrons.
• CHO and fats - are the major stores of fuel in
  the body, hence are the major electron donors.

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Energy Pathway 2
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Energy Pathway 2
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Energy Pathway 2

• Complete aerobic catabolism
• 1 Glycogen unit to water and CO2
• Yield 39 moles of ATP
• 3 from glycolysis
• 2 from TCA
• 34 from electron transport chain
• 1 Glucose unit to water and CO2
• Yield 38 moles of ATP

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Energy Pathway 3

• Aerobic phosphorylation of ADP using fatty acids
• Begins w/ conversion of 2-C chunks of fatty acids
  being converted to Acetyl CoA
• Process called beta-oxidation
• ATP yield from fat is always higher than CHOs
• Triglycerides fat stored in body
• 1 glycerol
• 3 fatty acid molecules

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Energy Pathway 3

• Triglycerides
• Broken down by lipase
• Process called lipolysis
• Once glycerol grp is removed FFA are formed.
• Move free in bloodstream
• Volatile Fatty Acids (VFA)
• Important fuel source
• Results from fermentation

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Energy Pathway 3

• Complete aerobic catabolism of palmitic acid
  (16-C fatty acid)
• Molecular formula C16H32O2
• Yields 129 molecules of ATP
• Total production 131 ATP
• 2 ATPs used to activate beta-oxidation
• Takes place outside of mitochondria

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Energy Pathway 3

• Once inside mitochondria
• 5 ATP made per 2-C released
• Chain is shorten by 2-C 7 times
• 5 x 7 35 ATP
• TCA cycle
• yields 8 ATP directly
• 88 ATP by oxidative phosphorylation
• Total 131 ATP
• Minus 2 ATPs activation of fatty acids
• Giving 129 ATP

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Energy Pathway 3
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Energy Pathway 3

• On a mass for mass basis
• 1 gram of fat is better than 1 gram of CHO
• When it comes to ATP yield
• Disadvantages of fat as a fuel
• Requires more oxygen to break down
• The speed of energy release from fat is much
  slower than from CHO
• Limited to trotting and slow-medium speed
  cantering
• Faster a horse runs the less it is able to use
  fat as an energy source.

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Energy Pathway 4

• Anaerobic phosphorylation of ADP using CHO
• Conversion of glycogen or glucose to lactic acid
  to yield ATP
• Pyruvate is converted to Lactic acid via lactate
  dehydrogenase (LDH )
• Lactic acid and lactate are interchangeable
• 3 ATP produced from glycogen
• 2 ATP produced from glucose

LDH
LDH Pyruvate NADH ------gt Lactate NAD H
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Energy Pathway 4

• Anaerobic energy production is inefficient but
  fast.
• Low ATP yielding
• Significant depletion of muscle glycogen
• Can be reduced by 1/3 after a single bout
• Fatigue prevents complete exhaustion of glycogen
  stores
• Feedback mechanism takes over
• Muscle pH change

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Energy Pathway 4
LDH
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Energy Metabolism