Bioenergetics of
Exercise and
Training
Objectives
• Defining essential terminology
• The role of ATP
• Three basic energy systems to
replenish ATP in skeletal muscle:
–Phosphagen, Glycolysis, and Oxidative
• How substrates are used and broken
down for energy production
• Contribution of each energy system to
physical activity
Energy
• The ability or capacity to
perform physical work
• Chemical:
– Work for synthesizing
cellular molecules
• Mechanical:
– Work of muscle
contraction
• Conversion of chemical
into mechanical is
necessary for movement
to occur
Bioenergetics Defined
• Conversion of food
• Chemical energy in carbohydrate, protein, and fat
molecules is converted into mechanical energy
• The breakdown of chemical bonds in these
molecules releases energy to perform:
– Muscular activity
– Digestion and absorption of food nutrients
– Glandular functions that secretes hormones
– Maintenance of electrochemical gradients
across cell membranes
– Synthesis of new chemical compounds and
tissues
Catabolic and Anabolic
• Catabolic:
– Breakdown of large molecules into smaller
molecules to release energy
– Carbohydrates = Glucose
– Fat = Fatty Acids and Glycerol
– Protein = Amino Acids
• Anabolic:
– The synthesis of larger molecules from smaller
molecules
– Formation of proteins from amino acids
Metabolism
• Metabolism:
–Total of all
catabolic and
anabolic
reactions in
the body
(build up and
break down of
food in the
body)
• Michael Phelps consumes
12,000 calories per day in
order to swim six hours a day,
six days a week. He swims
50 miles per week (a little
over 8 miles per training day).
ATP
• ATP is Adenosine
Triphosphate
• It contains a large
amount of chemical
energy stored in its
high-energy phosphate
bonds
• It releases energy
when it is broken down
(hydrolyzed) into ADP
(or Adenosine
Diphosphate).
ATP
• ATP is produced in the mitochondria to
power muscular activity
• Muscle cells only store a limited supply
of ATP and activities require a constant
supply of ATP for muscle contraction
• Three basic energy systems exist in
muscle cells to replenish ATP:
–The Phosphagen System
–Glycolysis
–The Oxidative System
Aerobic vs. Anaerobic
• Aerobic:
• Anaerobic:
– ATP synthesized – ATP generated rapidly
With Oxygen
for short durations
Without Oxygen
Three Energy Systems to Replenish ATP
• Phosphagen System:
– Anaerobic, synthesizes ATP
without oxygen
• Glycolysis:
–Two types: Fast (Anaerobic) and
Slow Glycolysis (Aerobic)
• Oxidative:
–Aerobic, requires oxygen
Energy Systems
• Fat and Glycogen are the major sources for
ATP resynthesis
• Some ATP comes from Creatine Phosphate
• Carbohydrates are the only macronutrient
that generate ATP anaerobically
• All three systems are active at a given time
• The fuel mixture that powers exercise
depends on the Intensity and Duration of
effort, and the exerciser’s fitness and
nutritional status
Creatine Phosphate (CP)
• Can be stored in the muscle and is made from
ATP during periods of rest
• During periods of high activity CP is broken down
quickly and its energy converted to ATP
• But this source of ATP can only supply a cell for 8
to 10 seconds during the most strenuous exercise
• Creatine released during muscle activity shows up
in the urine as creatinine
• Training can increase the amount of creatine
phosphate stored, but this alone does not increase
the strength of a muscle, just the length of time
before it runs out of CP
Enzymes
• ATPase breaks down ATP for form ADP
and P and release energy
• Creatine Kinase regulates the breakdown
of Creatine Phosphate
• These reactions provide energy at a high
rate; however ATP and CP are stored in
the muscle in small amounts
• The Phosphagen System cannot supply
enough energy for continuous long
duration activities
Phosphagen System
• At the beginning of exercise, ATP is
broken down into ADP releasing energy
for muscle contraction
• An increase in ADP activates creatine
kinase to form ATP from creatine
phosphate
• Creatine kinase remains elevated if
exercise continues at a high intensity
• If exercise is discontinued or continues at
a lower intensity Glycolysis or the
Oxidative Systems supply ATP
Phosphagen System
• Phosphagen concentration in muscle is more
rapidly depleted as a result of high intensity
anaerobic activity (plyometrics)
• Creatine phosphate is decreased and can
almost be eliminated as a result of very high
intensity
Phosphagen System
• Creatine phosphate can decrease
(50-70%) during high-intensity exercise (5-30
seconds) and can be almost eliminated as a result of
very intense exercise to exhaustion
• Complete ATP resynthesis can occur within 3-5
minutes of rest
• Complete creatine phosphate resynthesis can occur
within 8 minutes of rest
• Resistance training shows an increase in
phosphagens
• Type II fibers contain more phosphagens than Type I
Phosphagen System
ATP
ATPase
ADP + Creatine Phosphate
ADP + Pi + Energy
Creatine Kinase ATP + Creatine
Phosphagen System
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Volleyball
Gymnastics
Shot Put
Long Jump
High Jump
Pole Vault
Discus Throw
Javelin Throw
Hammer Throw
Figure Skating
• Baseball
• Diving
• Olympic Weight Lifting
(Snatch and Clean and
Jerk)
• Football
• Fencing
• Sprinting
• Tennis
• Golf
Glycolysis
• Glycolysis is the breakdown of carbohydrates
from glycogen stored in the muscles or liver or
glucose delivered in the blood to produce ATP
• Does not produce much ATP in comparison to
aerobic metabolism, but it has the advantage
that it doesn't require oxygen
• It occurs in the Sarcoplasm of the muscle cell,
not the mitochondria
• For intense exercise of 1 to 2 minutes (e.g.,
jumping rope) duration, glycolysis provides the
primary source of ATP
Glycolysis
• The process of Glycolysis occurs in two
ways
–Fast Glycolysis
–Slow Glycolysis
Glycolysis
• ATP must be supplied at a high rate (e.g.,
resistance training)
• The End Result of Glycolysis is Pyruvate
• Pyruvate comes from the breakdown of
carbohydrates
• Pyruvate can proceed in Two directions:
– Pyruvate can be broken down into Lactic Acid
and then Lactic Acid is broken down into
Lactate (Fast Glycolysis)
OR
– Pyruvate is shuttled to the mitochondria (Slow
Glycolysis)
Fast Glycolysis
• Lactic Acid:
–A waste product of glucose and
glycogen metabolism produced in
the muscles during intense exercise
• As lactic acid accumulates there is an
increase in hydrogen ion concentration
which interferes with muscle
contraction:
–Inhibiting calcium binding to troponin
–Interfering with actin-myosin cross
bridge formation
Fast Glycolysis
• Results in the formation of Pyruvate and
Hydrogens Ions (H+)
• A build up of H+ will make the muscle
cells acidic and interfere with their
contraction so molecules called
Nicotinamide Adenine Dinucleotide
(NAD+), remove the H+
• The NAD+ is reduced to NADH which
deposit the H+ in the mitochondria to be
combined with oxygen to form water
(H2O).
Fast Glycolysis
• The presence of Hydrogen Ions, not lactate,
makes the muscle acidic which will eventually
halt muscle function
• As hydrogen ion concentrations increase, the
blood and muscle become acidic
• This acidic environment will slow down enzyme
activity and ultimately the breakdown of glucose
itself
• Acidic muscles will aggravate associated nerve
endings causing pain and increase irritation of
the central nervous system (“The Burn”)
• An individual may become disorientated and
feel nauseous
Fast Glycolysis
• Lactic acid is converted to a salt called
Lactate in the muscle and blood
• Some of the Lactate diffuses into the
blood stream and takes some H+ with it
as a way of reducing the H+ concentration
in the muscle cell
• Lactate can be transported in the blood to
the liver, where it is converted to glucose.
• This process is referred to as the Cori
Cycle
Lactate Threshold (LT)
• The intensity at which lactate accumulates in
the blood or Onset of Blood Lactate
Accumulation (OBLA)
• Begins at 50-60% of VO2 in untrained
individuals and 70-80% VO2 in trained
individuals
• Aerobically and anaerobically trained
individuals have a faster lactate clearance rate
than untrained people
• The clearance of lactate from the blood
indicates a person’s ability to recover
• Lactate can be cleared within the muscle it was
produced
Fast Glycolysis
• Basketball
• Boxing
• Wrestling
• Football
• Ice Hockey
• Soccer
• Skiing
Slow Glycolysis
• If oxygen is present in sufficient amounts Pyruvate is
not converted to Lactic Acid but transported to the
Mitochondria
• When pyruvate enters the mitochondria it is converted
to Acetyl-CoA
• Acetyl-CoA:
– A form of acetic acid or vinegar
• Acetyl CoA can then enter the Krebs Cycle (Citric
Acid Cycle)
– A chemical cycle which completes the metabolic
breakdown of glucose molecules to carbon dioxide;
occurs within the mitochondria
Glycolysis
• Energy Yield of Glycolysis
–Glycolysis from one molecule of
blood glucose yields a net of two
ATP molecules
–Glycolysis from muscle glycogen
yields a net of three ATP
molecules.
Oxidative System
• Primary source of ATP at Rest
and during aerobic activities
• Uses primarily Carbohydrates and
Fats as fuels
• Protein is not metabolized except
during long-term starvation and
long bouts of exercise (90 minutes
or more)
Oxidative System
• Metabolism of blood glucose and
muscle glycogen begins with
glycolysis and leads to the Krebs cycle
• Recall: If oxygen is present in sufficient
quantities, the end product of
glycolysis, Pyruvate, is not converted
to lactate but is transported to the
mitochondria, where it is taken up and
enters the Krebs cycle
Oxidative System
• Krebs Cycle:
– A chemical cycle involving a series reactions
by which fragments from any of the energy
nutrients (carbohydrates, fats, and protein)
are completely broken down to carbon
dioxide and water, releasing energy for the
formation of adenosine triphosphate (ATP)
– The result is 38 molecules of ATP are
produced from 1 molecule of glucose
• It is the final common pathway for all nutrient
metabolites involved in energy production
Oxidative System
• Fat Oxidation
– Triglycerides stored in fat cells can be broken
down by hormone-sensitive lipase. This
releases free fatty acids from the fat cells into
the blood, where they can circulate and enter
muscle fibers.
– Some free fatty acids come from
intramuscular sources
– Free fatty acids enter the mitochondria, are
broken down, form acetyl-CoA and hydrogen,
and then enter the Krebs cycle
Oxidative System
• Protein Oxidation
–Protein is not a significant source of
energy for most activities
–Protein is broken down into amino
acids, and the amino acids are
converted into glucose, pyruvate, or
various Krebs cycle intermediates to
produce ATP
Oxidative System
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Cross country skiing
Long distance running
Long distance swimming
Rowing
Walking
Energy Capacity
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The Phosphagen System, does not require oxygen
to produce ATP
– High Intensity Short Duration Activities
• Fast Glycolysis uses glycogen stores in the muscle
and liver to produce ATP without oxygen
• Slow Glycolysis uses muscle and liver glycogen to
produce ATP and occurs in the presence of oxygen
– Both Fast and Slow: Moderate-to-High Intensity
Short to Medium Duration Activities
• Oxidative: uses carbohydrates and fats stored in the
body to produce ATP and requires oxygen
– Low Intensity Long Duration Activities
Energy Capacity
Duration
Intensity
Primary
Energy System
0-6 sec
Extremely High Phosphagen
6-30 sec
Very High
Phosphagen and
Fast Glycolysis
30 sec to 2 min High
Fast Glycolysis
2-3 min
Moderate
Slow Glycolysis
and Oxidative
3 min or more
Low
Oxidative
Energy Capacity
• The extent to which each of the three
energy systems contributes to ATP
production depends primarily on the
Intensity of muscular activity and
secondarily on the Duration.
• At no time, during either exercise or
rest, does any single energy system
provide the complete supply of energy
Interval Training
• Interval training is a method that can
emphasize the energy systems by using
predetermined intervals of exercise and
rest periods
–Much more training can be
accomplished at higher intensities
–Difficult to establish definitive
guidelines for choosing specific
work-to-rest ratios
Combination Training
• Combination Training adds aerobic endurance
training to the training of anaerobic athletes in
order to enhance recovery (because recovery
relies primarily on aerobic mechanisms).
– May reduce anaerobic performance capabilities,
particularly high-strength, high-power
performance
– Can reduce the gain in muscle girth, maximum
strength, and speed- and power-related
performance
– May be counterproductive in most strength and
power sports
Carbohydrates
• A carbohydrate-deficient diet rapidly
depletes muscle and liver glycogen
• Low carbohydrate levels profoundly affect
both anaerobic capacity and prolonged,
high intensity aerobic exercise
• A low carbohydrate diet makes it difficult
to engage in vigorous physical activity
• Exercise in a carbohydrate-depleted state
causes significant protein catabolism
Carbohydrates
• Repletion of muscle glycogen during
recovery is related to post-exercise
carbohydrate ingestion
–Repletion appears to be optimal if
0.7 to 3.0 g of carbohydrate per kg
of body weight is ingested every
2 hours following exercise
Fats
• Stored fat represents the body’s most plentiful
source of potential energy
• Fatty acid catabolism requires oxygen
• Rate of fat oxidation is slower than
carbohydrate
• Enhanced fat oxidation spares glycogen
• You need carbohydrates to burn fat efficiently
• Aerobic training increases fatty acid oxidation,
particularly the fatty acids derived from active
muscle during moderate intensity exercise
Protein
• Protein catabolism accelerates during
exercise as carbohydrate reserves deplete
• Individuals who train vigorously must
maintain optimal levels of muscle and liver
glycogen to minimize lean tissue loss and
deterioration in performance
• Regular exercise training enhances the
liver’s capacity to synthesize glucose
from non-carbohydrate compounds