Energy Transfer
During Exercise
McArdle, Katch, & Katch
Chapter 6
Immediate Energy: The ATP-PC
System
Immediate & rapid
supply of energy
almost exclusively
from high energy
phosphates ATP and
PCr within specific
muscles.
How much stored
within muscles?
Immediate Energy: phosphagens
ATP = 5 mmol/kg
PCr = 15 mmol/kg
For 57 kg female (20 kg muscle) = 400 mmol total
For 70 kg male (30 kg muscle) = 600 mmol total
Brisk Walk
Slow Jog
All-out Sprint
1 minute
20 – 30 sec.
6 – 8 seconds
Immediate Energy: phosphagens
Activities that rely almost exclusively on
stored phosphagens:
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Wrestling
Apparatus routines in gymnastics
Weight lifting
Most field events
Baseball
Volleyball
Short-Term Energy: Lactic Acid
System
To continue
strenuous exercise
beyond a brief period,
the energy to
phosphorylate ADP
comes from glucose
and stored glycogen
during anaerobic
process of glycolysis
Short-Term Energy: Lactic Acid
System
This occurs when oxygen supply is
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Inadequate or
Oxygen demands exceed oxygen utilization
Activities powered mainly by lactic acid
energy system
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Last phase of mile run, 400 m run
100 m swim
Multiple sprint sports: ice hockey, field
hockey, and soccer
Short-Term Energy: Lactic Acid
System
Blood Lactate Accumulation
Only when lactate removal
(Ld < La) is slower than
lactate production does
lactate accumulate.
During light & moderate
exercise, aerobic
metabolism meets energy
demands. Non-active
tissue rapidly oxidize any
lactate formed.
Short-Term Energy: Lactic Acid
System
Lactate begins to rise
exponentially at about
55% of healthy untrained
person’s max VO2.
Usual explanation is
relative tissue hypoxia.
Point of abrupt increase
in blood lactate is onset
of blood lactate
accumulation.
Short-Term Energy: Lactic Acid
System
Blood lactate threshold occurs at higher
percentage in trained individual’s capacity
due to:
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Genetic endowment, e.g. muscle fiber type, or
Local adaptations that favor less production of
HLa and more rapid removal rate. Endurance
trg. extends exercise intensity before OBLA.
Lactate formed in one part of an active
muscle can be oxidized by other fibers in
same muscle or by less active neighboring
muscle tissue.
Short-Term Energy: Lactic Acid
System
Blood lactate as an Energy Substrate
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Substrate for Gluconeogenesis in liver
Lactate shuttling between cells – supply fuel
Short-Term Energy: Lactic Acid
System
Ability to generate high lactate
concentration in maximal exercise
increases with specific sprint and power
training.
An anaerobically trained athlete can
accumulate 20 to 30% more blood lactate
compared to untrained subjects.
Possible reasons:

Increased intramuscular glycogen stores,
20% increase glycolytic enzymes, motivation.
Long Term Energy: the Aerobic
System
The use of oxygen by
cells is called oxygen
uptake (VO2).
Oxygen uptake rises
rapidly during the first
minute of exercise.
Between 3rd and 4th
minute a plateau is
reached and VO2 remains
relatively stable.
Plateau of oxygen uptake
is known as steady rate.
Long Term Energy: Aerobic
System
Steady-rate is balance of energy required and ATP produced.
Any lactate produced during steady-rate oxidizes or
reconverts to glucose.
Many levels of steady-rate in which: O2 supply = O2 demand.
Oxygen supply requires
1.
2.
Deliver adequate oxygen to muscles
Process oxygen within muscles
The Aerobic System
Oxygen Deficit: difference between total oxygen
consumed during exercise and amount that
would have been used at steady-rate of aerobic
metabolism.
Oxygen Deficit
Energy provided during the oxygen deficit phase represents a
predominance of anaerobic energy transfer from stored
intramuscular phosphagens plus rapid glycolytic reactions.
Steady-rate oxygen uptake during light & moderate intensity
exercise is similar for trained & untrained.
Trained person reaches steady-rate quicker, has smaller
oxygen deficit.
Maximum Oxygen Uptake
The point when VO2 plateaus with additional workloads.
Maximum VO2 indicates an individual’s capacity for
aerobic resynthesis of ATP.
Additional exercise above the max VO2 can be
accomplished by anaerobic glycolysis.
Fast- and Slow-Twitch Fibers
Fast Twitch Fibers (II)
Slow Twitch Fibers (I)
Fast Contraction Speed
Half as Fast as FT
High Anaerobic Capacity High Aerobic Capacity:
mitochondrial density,
aerobic enzymes
The Energy Spectrum
Relative contribution of
aerobic & anaerobic
energy during maximal
physical effort.
Intensity and duration
determine the blend.
Nutrient-related
Fatigue: severe
depletion glycogen.
Oxygen Uptake during Recovery
A. Light aerobic exercise
rapidly attains steady-rate
with small oxygen deficit.
B. Moderate to heavy
aerobic takes longer to
reach steady-rate and
oxygen deficit
considerably larger.
C. Maximal exercise
(aerobic-anaerobic) VO2
plateaus without matching
energy requirement.
Oxygen Uptake during Recovery
Four reasons why excess post-exercise
oxygen consumption (EPOC) takes longer
to return to baseline following strenuous
1.
2.
3.
4.
Oxygen deficit is smaller in moderate exercise
Steady-rate oxygen uptake is achieved versus
in exhaustive exercise never attained
Lactic acid accumulates in strenuous exercise
Body temperature increased considerably
more.
Oxygen Uptake during Recovery
Traditional “Oxygen Debt” Theory
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Alactacid oxygen debt: restoration of ATP &
PCr depleted during exercise, small portion to
reload muscle myoglobin & hemoglobin [fast].
Lactacid oxygen debt: to re-establish original
glycogen stores by resynthesizing 80% HLa
through gluconeogenesis (Cori cycle) and to
catabolize remaining HLa through pyruvic
acid (Kreb’s cycle) [slower phase].
Deficit and EPOC
Oxygen Uptake during Recovery
Updated Theory because disprove
traditional Oxygen Debt Theory.
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EPOC serves to replenish high-energy phosphates
and some to resynthesize a portion of lactate to
glycogen.
Significant portion EPOC attributed to thermogenic
boost that stimulates metabolism (Q10).
Other factors EPOC: 10% reloads blood O2; 2-5%
restores O2 in body fluids, including myoglobin; all
systems increased O2 need in recovery due to effects
of epinephrine, norepinephrine, and thyroxine.
Oxygen Uptake during Recovery
Time frame for lactate
removal post-exercise
Mass action effect: rate
proportional to amount of
substrate & product
present
Passive or Active
Recovery
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Optimum recovery steadyrate exercise: passive
Optimum recovery nonsteady rate: active
Oxygen Uptake during Recovery
Intermittent Exercise: interval training
Major advantage of interval training:
enable performance of large amounts of
exhaustive exercise & lower HLa
Exercise: Recovery Ratio
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1:3 ratio overloads immediate energy system
1:2 ratio to train short-term glycolytic system
1:1 ratio to train long-term aerobic system
Illustration References
Axen and Axen. 2001. Illustrated Principles of
Exercise Physiology. Prentice Hall.
McArdle, William D., Frank I. Katch, and
Victor L. Katch. 2011. Essentials of Exercise
Physiology 4th ed. Image Collection.
Lippincott Williams & Wilkins.
Plowman, Sharon A. and Denise L. Smith.
1998. Digital Image Archive for Exercise
Physiology. Allyn & Bacon.