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“Where Energy To train Comes From”
Overview
For most of our training life we simply ‘do it’ without thinking about the science, or concerned
concerned with how any human physical activity is fueled. However, if we want to get the best
out of our physical capabilities we should spend some time getting to understand the
mechanics of what fuels our activity.
Essentially, we are talking about the production of energy and the first thing to know is that
this is time and intensity related. It is obvious to state that, say, running at very high intensity,
as in sprinting, means an athlete can operate effectively for only a very short period. Running
at a low intensity, as in gentle jogging, means that an athlete can sustain activity for a long
period.
Training introduces another variable, and the sprinter who uses sound training principles is
able to run at a high intensity for longer periods. Similarly, the endurance athlete who uses
sound training methods can sustain higher intensities during a set period. There is also a
relationship between the exercise intensity and the energy source.
Central to the study of exercise physiology is energy. Exercise physiologists are interested in;
Where we get our energy to exercise from.
How we optimise our energy usage during exercise
How we recover our energy stores following exercise
This unit will look at how the body converts energy from food into energy for muscular
contractions which enable us to carry out physical exercise. This knowledge allows us to better
coach ourselves, and others in the martial arts, to maximum performance.
Energy exists, as we know, in a number of different forms - electrical, light, heat and we must
first understand that energy is never lost; it is constantly recycled, often from one form to
another. Boiling a kettle transfers electrical energy to heat. Similarly, energy found in the
chemical bonds of food fuels that we eat are transformed into mechanical energy, enabling us
to move. It is the conversion of chemical energy into mechanical and heat energy that this unit
is about.
Sources of Energy in the Body
For movement to occur, chemical energy must be transferred into mechanical energy and the
chemical energy is stored in an easy-access, energy rich compound called adenosine
triphosphate (ATP). ATP exists in all cells and consists of a number of atoms held together
by high energy bonds. It is through breaking down these bonds that energy is released. ATP is
the energy currency of cells and is the only direct source of energy for all energy-requiring
processes in the body.
When energy is required, the enzyme ATPase is released which initiates the breakdown of
ATP. It is the outermost bond of ATP that attracts ATPase as it is that bond that stores most
energy. Through the breakdown of ATP, energy is released leaving adenosine diphosphate
(ADP) and an inorganic phosphate (Pi). This process also gives off heat and is termed
exothermic. Through the breakdown of ATP, energy is released to help the heart beat,
muscles to contract and the brain to fire electrical impulses.
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There is, however, only a limited supply of ATP within the muscle cell, probably only enough
to perform maximal exertion for two to three seconds, such as a maximal weight lift or a sprint
start. If we had to carry an unlimited supply of ATP we would have to carry the body’s
equivalent weight around with us so, more practically, the body has adapted to becoming an
ATP ‘recycling machine.’
This recycling or resynthesising of ATP itself requires energy and this comes from the food we
eat. The fuels for ATP resynthesis are derived from the following sources;
Phosphocreatine (PCr) - a high-energy compound which exists in the muscles alongside
ATP and provides the energy for ATP resynthesis during high-intensity exercise. PCr is used in
the first 10 seconds of intense exercise and the close proximity of PCr to ATP in the muscle
helps this immediate synthesis, but, like ATP PCr stores are limited.
Glycogen (stored carbohydrate) - the form of carbohydrate stored in the muscles (350g)
and liver (100g), which is first converted into glucose before being broken down to release the
energy for ATP resynthesis. It is important to know that during high-intensity exercise,
glycogen can be used without the presence of oxygen (anaerobic metabolism). However, much
more energy can be released from glycogen during aerobic metabolism (when oxygen is
present).
Triglycerides (muscular stores of fat) - at rest, up to two-thirds of our energy requirement
is met through the breakdown of fatty acids (the component of fat used for energy
production). This is because fat can provide more energy per gram than glycogen (1g of fat
provides 9.1 kcal of energy compared to 4.1 kcal of energy for every 1g of glycogen). The
downside is that fat requires 15 per cent more oxygen than glycogen to metabolise, but it
remains the favoured fuel source at rest and during endurance (‘long/slow’) based activity. One
molecule (mole) of fatty acid typically yields around 130 moles of ATP.
Fats, as an energy source, need a plentiful supply of oxygen and the transport of fatty acids in
the blood is poor (slow) due to their insolubility, requiring the necessity for glycogen to be
present so as to provide supplementary energy for muscle contractions.
Proteins - the least favoured source of energy, only containing 5 to 10 percent of total energy
yield. In the presence of oxygen protein can be used as an energy provider if, say, glycogen
stores are low. Protein facilitates growth and repair of the body’s cells, such as muscle tissue
and are its primary functions.
The Three Pathways
The conversion, therefore, of these fuels into energy which can be used to resynthesise ATP
occurs through one of the pathways, or energy systems. Remember, it is the intensity and
duration of the exercise which dictates whether oxygen is present and, ultimately, which
system predominates. The three energy systems are;
1. ATP-PC or alactic system
2. The lactic acid system
3. The aerobic (oxidative) process
The more intense the exercise, the more the performer will rely on the production of energy
from anaerobic pathways such as the ATP-PC system, or lactic acid system. Heavy, stressful
and dynamic martial arts drills are fueled by these systems. If we separate the initial ATP
breakdown that ‘ignites’ us for the first 2/3 seconds we have four pathways.
1. The ATP-PCr (alactic)system
As we now know, ATP stores are depleted after about three seconds, so for high intensity effort
to continue, the immediate recycling of ATP is necessary, but without oxygen available (oxygen
deficit) during high intensity work, the body relies on PCr. Without getting too technical, this
breakdown takes place in the sarcoplasm (fluid that surrounds the muscle). PCr is broken
down by an enzyme, creatine kinase which will have been stimulated by the increase of
ADP and inorganic phosphate (both products of ATP breakdown as described above).
The initial ATP utilisation will be over before these athletes reach the first hurdle.
The issue to remember is that the breakdown of PCr is not used for muscle contractions, but
instead used to recycle ATP so that it can again be broken down. This reaction is known as
Endothermic. The ATP-PC system is of particular use to athletes who compete at high
intensity for about 10 seconds - such as 100m sprinters, or a martial artist performing an
intense combination of kicks and punches.
Advantages of the ATP-PC System
The resynthesis of ATP by PCr happens rapidly.
PCr stores are recovered very quickly, within 2-3 minutes of stopping exercise.
It is an anaerobic process so doesn’t need to wait for three minutes for sufficient oxygen to
be present.
There are no fatiguing by-products which could delay recovery.
Creatine supplementation has been shown to extend the time usage
Drawbacks are that PCr can only be restored when oxygen is present, say, during rest and
it’s usage is only about the 10 sec mark. So, for a 100m sprint, ATP will initially split to enable
the athlete to drive away from the blocks, with PCr breaking down to maintain a constant
supply of energy for the rest of the race.
2. The Lactic Acid (lactate anaerobic) System
The word threshold is used to describe the point where one energy system is exhausted and
another takes over as the predominant one and for most activity that lasts longer than the 10
second threshold of ATP-PC, the body switches to glycogen as the next fuel source to
resynthesise ATP. Stored in the liver and muscle, glycogen is first broken down into glucose–
6-phosphate, before it is broken down into pyruvate (pyruvic acid) by another enzyme in
a process known as glycolysis. The glycolysis also takes place in the sarcoplasm to facilitate
ATP resynthesis. This energy process will fuel an athlete for some 1 – 3 minutes and a 400m
runner is an obvious example of an athlete for whom this process is the ideal energy system.
Advantages of the Lactic Acid System
Because there are few chemical reactions, ATP can be resynthesised relatively quickly for
bouts of exercise that take place between 10 secs – 3 mins.
It is an anaerobic system and therefore doesn’t need to wait 3 minutes for sufficient oxygen.
Any lactic acid produced as a by-product can be converted back into liver glycogen.
Even during long aerobic activities, i.e. 10k run, the lactic acid system can be called upon
to produce an extra burst of energy, for example, a sprint finish.
Drawbacks of the lactic system are first, the accumulation of lactic acid which make glycotic
enzymes acidic, causing them to lose their catalytic ability, inhibiting further energy
production by glycolysis. Activity, therefore, has to be reduced or stopped; only a small amount
of energy is locked in a glycogen molecule (approx. 5%), that can be released in the absence of
oxygen (the remaining 95% can only be released in the presence of oxygen).
3. The Aerobic System
During resting conditions, or where demands for energy is low, oxygen is readily available
(hence the name – aerobic system) to release stored energy from glycogen, fats and proteins.
The aerobic system is the body’s preferred energy pathway, as it is, by far, the most effective in
terms of ATP resynthesis – the yield from aerobic metabolism is some 18 times greater than
anaerobic processes.
As outlined above, under anaerobic conditions, pyruvic acid (pyruvate) is converted into a
fatigue-inducing lactic acid. However, when oxygen is present, pyruvic acid is instead
converted into acetyl–coenzyme-A by combination with an enzyme with an even longer
name! This reaction now moves, from taking place in the sarcoplasm, to the mitochondria.
Mitochondria are known as the ‘powerhouse’ of the cell, being specialised structures within all
cells that are the site of ATP production under aerobic conditions. Mitochondria are the
ultimate destination of the oxygen that we breathe in. It is inside these ‘factories’ that all our
aerobic energy is produced. The more fit we are the more and larger mitochondria we possess.
If we remember the work on the previous Unit on muscle types, it is interesting to note that
‘slow twitch’ muscle fibres house many more mitochondria than ‘fast twitch’ fibres and, hence,
are more suited to aerobic activity, such as marathon running.
Two Stages of the Aerobic System
Without going into the complicated mechanisms of these two systems, we should know that
these are;
1.The Kreb’s Cycle
2.The Electron Transport System
As mentioned, earlier, it is not only glycogen that can be utilised in the aerobic energy system
and long, endurance exercise will use a mixture of both glycogen and fats and also, reluctantly,
protein. By preference, the body will look to fats for its greatest energy return, thereby sparing
glycogen for later in the event, when intensity may increase. Water and carbon dioxide are byproducts of these processes.
Advantages of the Aerobic System
Significantly more ATP can be resynthesised under aerobic conditions than anaerobic (36
ATP aerobically to 2 ATP anaerobically from one mole of glycogen).
The body has substantial stores of muscle glycogen and triglycerides to enable exercise to
last for hours.
Oxidation of glycogen and fatty acids do not produce any fatiguing by-products.
Drawbacks of the system are that from a resting state to exercise, it takes a while for
sufficient oxygen to become available to meet demands; although fatty acids are the fuel during
endurance events, fatty acid transport is slow and requires 15% more oxygen than required to
break down the same amount of glycogen; glycogen is required alongside fatty acids, but if it
becomes depleted and the body attempts to metabolise fatty acids as a sole source of fuel,
muscle spasms may result – commonly known as ‘hitting the wall’.
Energy Profiling
This term is used to describe the importance of each energy system to a particular activity. In
reality, the 3 energy systems work alongside each other, each contributing different amounts of
energy to resynthesise ATP. We can think of the relationship to fuel states and specific sports
in 3 blocks;
AT P - P C
LACTIC
35%
35%
ACID
AEROBIC
30%
This block diagram illustrates the energy profile of a squash player who will, largely, use
anaerobic systems during each point. However, the aerobic system will be called upon between
points and games to ensure swift recovery.
By contrast, if we thought about the energy profile of a traditional karate competitor, he or she
will spend by far the majority of his or her time utilising the ATP and ATP– PC for an attack
or defence with if the exchange continues for more than 3 seconds - rarely are exchanges longer
than 10 seconds.
Whilst waiting to attack or defend the aerobic system may have come into play, but not if the
fight is over quickly. What should take place, prior to the fight, is a warm-up period, so as to
bring the aerobic system into play, which will then continue to function between the high
energy activity.
Improving Efficiency
Whatever our particular training needs, we should try to improve the efficiency of our energyproducing systems. There are a number of support systems that can be brought into play;
1.Glycogen Loading - favoured by endurance athletes, seeks to deplete the body’s
glycogen levels seven days prior to the event, through endurance based training and
carbohydrate avoidance and then, with three days to go, consuming a diet rich in
carbohydrates with little or no exercise.
2.Creatine Supplementation - used to extend the threshold of the ATP-PC system by
ingesting creatine monohydrate, although some people may experience stomach
problems.
3.Soda Loading - is a method of neutralising the negative effects of lactic acid by
ingesting bicarbonate of soda, thereby increasing the blood’s pH ‘buffering’ it against
the effects. Again, stomach problems are likely.
4.Training - various training regimes can be used to improve the efficiency of each of the
three energy pathways. The following highlights those that have a direct impact on
ATP resynthesis, as we know that many other adaptations also occur with all
programmes.
Some Training Regimes to Improve Efficiency
ENERGY
SYSTEM
D U R AT I O N E X A M P L E S T R A I N I N G A DA P TAT I
OF
OF
ON
METHOD
ACTIVITY ACTIVITY
FOLLOWIN
G
TRAINING
ATP-PC
Lactic Acid
System
3 to 10
seconds
•100m sprint
•Gym Vault
•10 seconds to •400m run
3 minutes
•100m swim
•Squash rally
Aerobic
System
•Over 3 mins
•Marathon
•Triathlon
•Recovery
during events
•Sprint
interval
training
•Increased
stores of ATP
and PC
•Plyometrics
•Increased
activity of
ATPase and
creatine
kinase
•Weight
training
(80-95%
1RM/4-8 reps)
•Interval
•Increased
training
stores of
muscle
•Fartlek
glycogen
•Weight
•Increased
training
number of
(65-80%
glycolytic
1RM/8-15
enzymes
reps)
(PFK)
•Circuit
training
•Continuous •Increased
training
•Fartlek
•Distance
Interval
training
muscle
glycogen and
triglycerides
•Increased
number of
oxydative
enzymes
One way to think about energy pathways is that they are ‘time duration restricted’ although
there is some disagreement about the actual threshold points, but the key issue is exercise
intensity. We haven’t dealt with food types in this unit and it is up to students to make their
own links between food types and energy sources.
In later units we will look at combat training and fitness routines and the factors that
contribute to successful performance, irrespective of its nature. We may be coaching full
contact competitors, police officers, members of the public with little, or no physical activity
history, or particularly fit individuals, but who are not ‘fit specific’ for high intensity combat
oriented drills.
Peter Consterdine can be contacted at the British Combat Association
www.britishcombatassociation.co.uk and also at www.peterconsterdine.com