Exercise Science
BIOENERGETICS
Bioenergetics
• Conversion of macronutrients into
biologically usable forms of energy.
– Macronutrients - found within food
• Carbohydrates, proteins, fats
– Energy – ability or capacity to perform work
• Stored in chemical bonds
Bioenergetics
• Macronutrients
substrates
– Phosphagen
– Glucose
– Glycogen
– Lactate
– Free fatty acids
– Amino acids
Metabolism
• Metabolism – total of all chemical reactions
• Catabolism - breakdown of larger molecules
into smaller molecules
• exergonic reactions – energy is released
• i.e.: proteins → amino acids
• Anabolism - synthesis of larger molecules from
smaller molecules
• endergonic reaction – energy is required
• i.e.: amino acids → proteins
Adenosine Triphosphate –
‘ATP’
• Allows the transfer of energy
– catabolic
anabolic
• Required for all activity & growth
• Limited stores of ATP
• ATP Hydrolysis
– The breakdown of 1 molecule of ATP to
yield energy; requires 1 molecule of water
– Requires presence of ATPase
Bioenergetics
ADP Phosphorylation
(Endergonic/
Anabolic)
ATP Hydrolysis
(Exergonic/
Catabolic)
ATP
Energy
Energy
Pi
+
ADP
Biological Energy Systems
• ATP replenishment
Phosphagen system
• Phosphocreatine
Glycolytic system
• Carbohydrates (glucose)
Oxidative system
• Fats (free fatty acids)
• Protein (amino acids)
ATP
Phosphagen System
– Creatine Phosphate (CP or PCr) - energy
reserve for rapidly replenishing ATP
• stored in limited amounts
– Short-term, high intensity activities
– Active at the start of all exercise; 0 – 6 s
Glycolysis
• Breakdown of glycogen or glucose to
resynthesize ATP
– End product - pyruvate
• Anaerobic Glycolysis (fast glycolysis)
– Pyruvate converted to lactate
• Aerobic Glycolysis (slow glycolysis)
– Pyruvate shuttled into mitochondria to
undergo the Krebs cycle (citric acid cycle)
Fast & Slow Glycolysis
Glucose/Glycogen
Fructose-6-phosphate
Slow
Glycolysis
Fast
Glycolysis
Fructose-1, 6-bisphosphate
Pyruvate
Pyruvate
Krebs
Cycle
Lactate
Lactate
Anaerobic (Fast) Glycolysis
• Result of insufficient 02
• Pyruvate → Lactate (La-)
– Lactate clearance
• Oxidation in muscle fibers
• Transported to Liver
– Cori Cycle
– Gluconeogenesis occurs
» La- → Glucose
Aerobic (Slow) Glycolysis
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– Sufficient O2
– Pyruvate is shuttled to the mitochondria
– Pyruvate → acetyl-CoA
– Acetyl-CoA enters the Krebs cycle
Control of Glycolysis
Rate is affected by regulatory enzymes:
• hexokinase
• phosphofructokinase
• pyruvate kinase
• Stimulated by
– high concentrations of
• ADP, Pi & ammonia
– slight decrease in
• pH & AMP
• Inhibited by
– markedly lower
• pH, ATP, CP, citrate & FFA
• Note:
– slight ↓ of pH stimulates
– significant ↓ of pH inhibits
Lactate Threshold and OBLA
Lactate Threshold (LT)
OBLA
• Abrupt ↑ lactate
• ↑ reliance on anaerobic
mechanisms
• Affected by level of training
• Onset of Blood Lactate
• 2nd inflection point of
lactate accumulation
• Corresponds with
intermediate & large
muscle fiber recruitment
– Untrained ~ 50-60% VO2max
– Trained ~ 70-80% VO2max
Effect of Training on Lactate
• Training near LT or OBLA shifts the curve
right
– Performance at higher % of VO2max
• Muscular fatigue
– Most likely a result of H+ accumulation from
ATP hydrolysis
(No longer thought to be lactate accumulation)
Lactate Threshold and OBLA
Oxidative Energy System
• Primary source of ATP at rest and during
low-intensity activities
– At rest
• 70% fat & 30% carbohydrate
– Onset of activity
• Shift in preference from fat to carbs
– Prolonged, submaximal, steady-state work
• Shift from carbs back to fats and protein
Oxidative Energy System
• Glucose & Glycogen Oxidation
– Pyruvate shuttled to the mitochondria
• Converted to acetyl-CoA
• Acetyl-CoA enters the Krebs Cycle
• NADH & FADH2
– Produced during glycolysis & Krebs cycle
– Transport H+ to Electron Transport Chain (ETC)
– Hydrogen used to produce ATP from ADP
Oxidative Energy System
• Fat Oxidation
– Triglycerides broken down by lipase to free
fatty acids (FFA)
– FFA carried by blood to muscle fibers
– Beta Oxidation:
• FFAs converted to acetyl-CoA and H+ in the
mitochondria
• Acetyl-CoA enters the Krebs Cycle
• H+ carried by NADH & FADH2 to ETC
Oxidative Energy System
Protein Oxidation
• Not a significant source of energy
• Amino acids (BCAA’s) first converted to:
– glucose (Gluconeogenesis)
– pyruvate or other substrates
• During prolonged activity, may
contribute 3-18% of energy requirement
Energy Yield from Oxidation
Oxidation of One Glucose Molecule
ATP Production
Slow Glycolysis
10
Krebs Cycle
30
Net ATP (ATP use varies*)
Oxidation of One Triglyceride Molecule
36/38
ATP Production
1 molecule of glycerol
22
18-carbon fatty acid metabolism
441
Total (varies with type of triglyceride)
443
Need not memorize these numbers!
Energy: Effects of Duration and Intensity
Duration
Intensity*
Primary System
0-6s
Extremely
High
Phosphagen
6 - 30 s
Very High
Phosphagen & Fast
Glycolysis
30 s – 2 min
High
Fast Glycolysis
2 - 3 min
Moderate
Fast Glycolysis &
Oxidative
> 3 min
Low
Oxidative
* Intensity dictates duration and the primary energy system
Energy Continuum
Creatine Phosphate
Aerobic Glycolysis
Anaerobic Glycolysis
Beta Oxidation of Fat
Energy Substrates
• Depletion of energy substrates = fatigue
– phosphagen
– glucose/glycogen (carbohydrates)
– lactate
– free fatty acids (triglycerides)
– amino acids (protein)
• Most often depleted:
– phosphagen and glycogen.
Substrate Depletion/Repletion
• Phosphagens
– Depletion due to high-intensity anaerobic exercise
– Repletion within 8 min. due to aerobic
metabolism
• Glycogen
– Depletion limits long-duration, low-intensity
exercise & repeated, very high-intensity exercise
– Repletion may take up to 24 hours
• optimal with ingestion of O.7 – 3.0 g/kg every 2 hr
Bioenergetic Limiting Factors
ATP &
CP
Muscle
Glycogen
Liver
Glycogen
Fat
stores
Lower
pH
1
5
4-5
2-3
1
Moderate (1800 m
run)
1-2
3
2
1-2
2-3
Heavy (400 m run)
3
3
1
1
4-5
Very Intense
(discus)
2-3
1
1
1
1
Very Intense,
repeated
4-5
4-5
1-2
1-2
4-5
Exercise
Light (Marathon)
Note: 1 - lowest probable limiting factor, 5 – most probable limiting factor
Oxygen Uptake
• Measurement of ability to take in and
use oxygen = VO2
• Oxygen deficit
– Actual VO2 < VO2 need
– ATP production via anaerobic mechanisms
– Influencing factors
• Training
• Intensity
• Muscle mass
involved
• Individual
differences
Excess Post-Exercise Oxygen
Consumption (EPOC)
• Oxygen uptake after exercise
• Oxygen needed to restore body to preexercise condition
• Possible factors
• Synthesis of ATP &
PCr
• Removal of lactate
• Replenish glycogen
stores
• O resaturation
• Intensity
• Individual differences
• ↑ Temperature
• ↑ Cardiorespiratory
Low-intensity, steady-state
exercise metabolism
High-intensity, non-steady-state
exercise metabolism
Metabolic Specificity Training
• Specific exercise intensities & rest
intervals (work-to-rest ratios)
• Allows for optimal training of an energy
system specific to a sport
• Methods
– Interval training
– Combination training
Interval Training
• Predetermined intervals of exercise and
rest
– More work can be accomplished at a higher
intensity
% Max
Power
Primary System
Duration
Work-to-Rest
Ratio
90 - 100%
Phosphagen
5 – 10 s
1:12 to 1:20
75 - 90%
Fast Glycolysis
15 - 30 s
1:3 to 1:5
35 - 75%
Fast Glycolysis &
Oxidative
1 min
1:3 to 1:4
20 - 35%
Oxidative
> 3 min
1:1 to 1:3
Combination Training
• Addition of aerobic endurance work to
enhance recovery of anaerobic athletes
– May result in
• ↓ anaerobic performance
• ↓ muscle girth
• ↓ max strength
• ↓ speed- and power-related performance
End
of
Section