Energy systems
•Energy for muscular contraction during exercise comes from
the splitting of a high energy compound (ATP).
•3 systems – adenosine triphospate (ATP PC), Lactic acid
system and the aerobic system
•ATP stored in very small amounts in the muscles (enough to
provide for maximal contraction for about 1 second.
•All 3 energy systems are activated at the start of exercise, with
the relative contribution being determined by the intensity and
duration of exercise. All 3 work together.
Foods and their conversion to
energy
• Food is taken into the body as chemical energy
and converted into mechanical energy in the
form of muscular contractions and movement.
• Food – digested, broken down, nutrients
absorbed, waste to the bowel. Nutrients carried
off via the bloodstream. Some fuel is used
immediately whilst others is stored around other
parts of the body.
• Carbohydrates, fats and protein are the only
sources of food energy and fuel.
Carbohydrates
• Sugars and starches found in fruit, cereal,
bread, pastas and vegetables. Body’s
preferred source of fuel, particularly during
exercise. Carbohydrates are the primary
energy source during anaerobic exercise of
high intensity and short duration.
Carbohydrates are broken down and stored as
glucose in the blood and glycogen in the
muscles and liver. Excess carbo’s are stored
around the body as adipose tissue.(fat tissue)
Fats
• Fats include butter, oils, nuts. Fat is the
body’s preferred source of fuel at rest.
More oxygen is required by the body to
use fat as a fuel than to use carbo’s to
produce ATP. Fats have the capacity to
produce much more ATP than carbo’s
however the conversion rate is much less
efficient since they require much more
oxygen to produce and equivalent amount
of ATP.
• Fatty acids are stored in the blood,
triglycerides in the muscles and excess
fats are stored as adipose tissue around
the body.
Protein
• Protein include meat, fish, poultry, dairy,
eggs and lentils. Protein is used for growth
and repair of the body and as fuel source in
extreme situations. Body only uses protein
as energy source when glycogen and fat
sources have already been depleted. Ie.
marathon or starvation
Food fuels at rest and during
exercise
•
At rest – aerobic energy system utilises both fats (2/3)
and carbohydrates (1/3) as preferred fuel because they
do not generate by products which cause fatigue.
• During exercise – both anaerobic and aerobic systems
contribute energy for ATP resynthesis during exercise.
• Several factors determine which system is the major
contributor of energy – duration and intensity as well as
training.
1. Short duration ie 100m sprint – anaerobic system
supply most of the required energy (carbo’s)
2. For prolonged submaximal (low intensity) aerobic
system is preferred system with carbo’s initially. As
glycogen stores depleted, fat mainly becomes the
energy source.
Energy systems –
what are they?
•
•
2 anaerobic systems are ATPPC system and the lactic acid
system – does not depend
upon the transportation of
oxygen to the working
muscles
Aerobic system is produced
with oxygen.
3 Energy systems
•
•
•
ATP-PC system (alatacid,
creatine phosphate or
phosphogen system)
Lactic acid system (anaerobic
glycolysis or lactic acid
system)
Aerobic system (oxygen
system)
3 basic pathways responsible
for the resynthesis or
rebuilding of ATP (energy
supply). Depends upon :
duration and intensity of
3 energy systems
•
At rest demands for energy
are low and can be met
aerobically.
•
Exercise increases the demand for ATP
because we can not increase our oxygen
intake and transport to the working
muscles as rapidly as is required by
explosive activities, our body calls upon
the 2 anaerobic systems in the early
(initial) stages of exercise to supply ATP.
If the exercise is longer in duration and
less intense, then the aerobic energy
system will be called upon to supply most
of the energy.
ATP-PC system
• Phosphocreatine (PC) (also known as creatine phosphate)- high
energy fuel stored in small amounts in muscles.
• Broken down to ADP+P (adenosine diphosphate + phosphate)
during muscle contraction.
• As rapidly as ATP is broken down to enable movement, it is
being reformed by the energy released when PC is broken
down.
• Advantage – immediate
• Disadvantage – limited by amount of PC stored in muscle
• Used at onset of work (short duration/high intensity/explosive
activities) maximum high intensity activity for 5 secs about 50%
of PC stores depleted. Ie short sprints, field events, spiking in
volleyball.
• Maximum contractions at maximal effort for 10-15 secs
• 30 secs rest for 50% replenishment 8-10 mins for 100%
replenishment
Lactic Acid System
• Anaerobic glycolysis system – carbo’s are broken down to glucose
and stored at the muscles and liver in the form of glycogen. ATP
must be reformed and replaced from ADP and Pi (a free Phosphate
molecule0, but again, this requires energy. This energy is obtained
from glycogen. Glycolysis is the process of breaking down glycogen.
Because oxygen is not present, the glycogen is not totally broken
down and a toxic waste called lactic acid is formed. This causes
muscular fatigue.The lactic acid system provides a stopgap until
sufficient oxygen can be transported to the working muscles for the
aerobic system to become the major contributor. Lactic acid system
is activated at the start of intense exercise. Peak power from this
system is reached between 10 -15 seconds will last for 2 -3 mins
before fatigue.
• Anaerobic threshold is a term used to describe the point at which the
anaerobic production of energy leads to the accumulation of lactic
acid in the blood, usually occurring at around 85% max heart rate
during exercise.
Aerobic System
• Uses oxygen and is the most powerful (has
greatest ability to supply ATP) Aerobic energy
system will be the major energy contributor for
extended endurance activities that remain below
85%
• Aerobic system uses the Krebs cycle and the
electron transport chain to produce ATP.
Aerobic System
• 3 stages in aerobic energy production,
responsible for the release of energy.
Stage 1 – fats and carbo’s broken down to release
energy. Fats stored as triglycerides, are broken
down releasing small amounts of energy for
basic body functions and low intensity activities.
Carbo’s (also used in lactic acid system) are
used to provide energy in the aerobic system.
Difference is that sufficient oxygen is supplied glycogen broken down to glucose and pyruvic
acid with energy made available for ATP
resynthesis. (Aerobic glycolysis). No toxic waste
ie lactic acid.
Aerobic System
• Stage 2 – krebs cycle – involves pyruvic
acid being broken down into carbon
dioxide with further energy being released
to resynthesise ATP.
Aerobic System
• Stage 3 – electron transport stage – involves
water (perspiration), heat and large amounts of
ATP being released. Aerobic system
preferentially breaks down carbo’s rather than
fats to release energy, however fats can produce
more ATP than carbo’s but require more oxygen
to produce an equivalent amount of ATP.
Aerobic system is fatigue resistant. Primary
source for endurance activities. Aerobic
production of energy occurs within the muscle
cell, this involves the breakdown of carbo’s and
happens in the mitochondria cell.