Energy System responses to acute
exercise
Energy systems: phosphocreatine; lactic acid;
aerobic; energy continuum; energy
requirements of different sport and exercise
activities
ATP
PC
Lactic Acid
Aerobic
Energy Systems & Exercise: The Basics
0 sec
ATP
4 sec
10 sec
1.5 min
3 min +
Strength – Power:
power lift, shot put, golf swing
ATP-PC (phosphagen)
Lactic Acid/Anaerobic Glycolysis
Sustained Power:
sprints, fast breaks, football
Anaerobic Power – Endurance:
200-400 m dash, 100 m swim
Aerobic Endurance:
Beyond 800 m run
Aerobic System
Immediate/short-term
non-oxidative systems
Aerobic-oxidative
system
Fuel, Energy systems & Exercise
• Anaerobic Energy System =
Carbohydrates are the only fuel source
• With prolonged exercise, Carbohydrates are the first fuel choice, as exercise
continues, FAT becomes predominant :
• As exercise intensity , energy supplied by Carbohydrates 
• As duration , energy supplied by fat 
• Protein is not a main fuel source except in an emergency :
• As glycogen , energy supplied by protein 
• Each system plays an important role in energy production:
• All energy systems are “on” at all times
• This gives us a variety of movements
• The systems interact to supply Energy for the activity
Fuel, Energy systems & Exercise
% energy from FAT
40 30 20 10
% energy from CHO
40 60 80 100
As exercise gets harder, the % energy from
oxidation of Carbohydrates goes UP sharply while
the % energy from fat goes DOWN
increasing intensity of exercise
Energy Systems on a Continuum!
‘All energy systems are “on” at all times’

All three energy systems contribute
at the start of exercise but the
contribution depends upon the
individual, the effort applied or on
the rate at which energy is used.

The following graph shows how the
energy systems contribute to the
manufacture of ATP over time when
exercising at 100% effort.

The thresholds (T) indicate the point
at which the energy system is
exhausted - training will improve the
thresholds times.
Energy Systems on a Continuum!
ADENOSINE
TRIPHOSPHA
TE
(ATP)
PHOSPHOCREATINE
(PCr)
GLYCOLYSIS
(ANAEROBIC;
CHO BREAKDOWN)
KREBS
CYCLE
(AEROBIC;
CHO, FAT, AND
PROTEIN
BREAKDOWN)
Energy Systems working together:
100m SPRINT
(10 seconds of maximal exercise)
Energy Systems on a Continuum!
ADENOSINE
TRIPHOSPHA
TE
(ATP)
PHOSPHOCREATINE
(PCr)
GLYCOLYSIS
(ANAEROBIC;
CHO BREAKDOWN)
KREBS
CYCLE
(AEROBIC;
CHO, FAT, AND
PROTEIN
BREAKDOWN)
Energy Systems working together:
800 METER RUN (50 seconds)
Energy Systems on a Continuum!
ADENOSINE
TRIPHOSPHAT
E
(ATP)
PHOSPHOCREATINE
(PCr)
GLYCOLYSIS
(ANAEROBIC;
CHO BREAKDOWN)
KREBS
CYCLE
(AEROBIC;
CHO, FAT, AND
PROTEIN
BREAKDOWN)
Energy Systems working together:
MARATHON 2.5 hours of exercise
Sport, Exercise and Energy Systems
Anaerobic
Wt. Training
Gymnastics
Football
Baseball
70-80% Anaerobic
20-30%
Aerobic
Stop & Go Sports
Tennis
Soccer
Field Hockey
Aerobic
Jogging
Marathons
Cycling
Aerobic Dance
Energy System recruitment in Sport
Sport
ATP-CP and LA %
LA-Aerobic
%
Aerobic
%
Basketball
Fencing
Field events
Golf swing
Gymnastics
Hockey
Distance running
60
90
90
95
80
50
10
20
10
10
5
15
20
20
20
Rowing
Skiing
Soccer
Sprints
Swimming 1.5km
20
33
50
90
10
30
33
20
10
20
50
33
30
Tennis
Volleyball
70
80
20
5
10
15
5
30
70
70
Table adapted from Fox E. L. et al, The Physiological Basis for Exercise and
Sport, 1993