1. Chapter 5: Food fuels and the three
energy systems
Thinking things through
Thinking things through p. 117
1 Foods not appearing in Figure 5.1 that are high in:
Carbohydrates Fats Proteins
Muffins Butter Low fat yoghurt
Plain yoghurt Ice cream (contains milk fat) Roast beef/chicken
Brown rice Chicken/Meat fat Protein bars
Corn Palm oil Whey
Peas Coconut oil Fish
Sugar Beef Soy beans
Lollies Lamb Tofu
Potato and sweet potato Veal Cottage cheese
Cakes, sweets, doughnuts
2 Recommended carbohydrate intake would exceed levels in a balanced diet in the following
sporting situations:
Athletes who undertake large amounts of aerobic training such as swimmers, marathon/
triathlon competitors, etc. who need to refuel throughout the training session/day
Athletes consuming larger amounts of carbohydrates than recommended intakes
because they are carbohydrate loading for endurance competitions in several days time
Sports people who undertake more than one training session per day (morning and
afternoon)
3 a The 20 km athlete would consume more low GI foods to ensure constant and slow release
during her/his event. It would take an elite 20 km runner upwards of 1 hour and 10 mins to
complete the activity. Carbohydrate loading would not be a big advantage as adequate
amounts should be present from a balanced diet. It is likely the 20 km athlete will try to
increase hydration levels and stored water in cells prior to the event.
b It is likely that rugby players would consume higher amounts of protein to assist muscle repair
due to the contact nature of the game. The 20 km runners would have higher loss of
carbohydrates to fuel their activity and hence consume larger amounts post event than the
rugby players.
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2. 4
Carbohydrates Fats Proteins
Complex carbohydrates can be Peanuts and other nuts Nuts: hazels, brazils,
found in cereals/grains (bread, Avocados almonds, cashews,
rice, pasta, oats, barley, millet, Olive and other plant oils walnuts, pine kernels, etc.
buckwheat, rye) and some Soya beans Seeds: sesame, pumpkin,
root vegetables, such as sunflower, linseeds.
potatoes and parsnips. Pulses: peas, beans, lentils,
A healthy vegetarian diet peanuts.
should contain plenty of these Grains/cereals: wheat (in
complex starchy carbs as they bread, flour, pasta etc.),
are beneficial for health, barley, rye, oats, millet,
weight and energy levels. Less maize (sweetcorn), rice.
refined complex carbs, like Soya products: tofu,
whole wheat bread, whole tempeh, textured
wheat pasta and brown rice, vegetable protein, vegie
are best of all because they burgers, soya milk.
contain essential dietary fibre Dairy products: milk,
and B vitamins cheese, yoghurt (butter
and cream are very poor
sources of protein).
Free range eggs.
Thinking things through p. 122
1 Answers will vary.
2 Answers will vary.
Thinking things through p. 123
1 Glycogen sparing occurs when fats are basically used as a source of energy during the early
stages of exercise so that the depletion of muscle glycogen stores is delayed. This leaves more
glycogen for the later stages of exercise and muscle fatigue will be delayed because the
changeover to fats as the main fuel source is also delayed. This only occurs in events lasting
longer than the typical time it takes for fats to take over from carbohydrates as the main fuel
producing ATP/energy i.e. 2+ hours.
2 Originally, carbohydrate loading involved a depletion phase, which is also known as ‘glycogen
stripping’, that included three to four consecutive hard training days while on a low-
carbohydrate diet. The depletion phase was thought necessary to stimulate the enzyme
glycogen synthase. The depletion phase was followed by a loading phase in the lead-up to
competition, which involved three to four days of rest combined with a high-carbohydrate diet.
The extra carbohydrate combined with the now-activated glycogen synthase was shown to
boost carbohydrate stores beyond their usual resting levels, which is known as the
supercompensation effect. This strategy, while increasing carbohydrates available for
performance, led to significant disruptions to preparation and training and has since been
refined so that modern-day carbohydrate loading is now more manageable and less disruptive
for athletes. Researchers and physiologists have demonstrated that athletes simply consuming a
high carbohydrate diet (70–75 per cent total dietary intake) for three days prior to competition
resulted in carbohydrate stores comparable to those individuals who performed the ‘glycogen
stripping’ method.
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3. 3 Having a higher percentage body fat would be advantageous where insulation is not readily
provided by clothing due to its restrictive nature e.g. swimming the English Channel or other
extended endurance swimming challenges. By having higher body fat content women are more
buoyant in water and this would be also an advantage because less energy is required to
maintain a horizontal position in water when swimming. In extended endurance events where
athletes may dip into their protein reserves to produce ATP, women having a higher percentage
body fat would delay or totally prevent this from happening. This would only be significant in
events lasting longer than 10 hours without opportunities to refuel.
Thinking things through p. 131
1 Greater contribution from the anaerobic glycolysis or LA system compared to first 200 m.
2 PC is depleted at the same rate in both 200 m sections of the race but the amount depleted
during the first 200m is significantly greater than that depleted in the second 200 m. Over 80%
of CP is depleted in the first 200 m of the race.
3 ATP is depleted at quicker rates than CP.
4 ATP is split quicker then CP due to less chemical reactions being required to liberate energy.
5 Lactate first appears in the muscles and signals imminent fatigue resulting from acidosis and
effects on glycolytic enzymes. It is then shunted to muscles with lower lactate concentrations
and is picked up in blood measurements. By this later stage it is often difficult to counteract the
fatiguing effect on performance.
Thinking things through pp. 138–9
1
No oxygen is required/ available
Rapid splitting of PC to produce energy, much quicker than any of the food fuels
PC stored at muscles more readily available than glycogen stored at the muscles
2 Fuels utilised by the LA system take longer to be broken down than PC and hence the rate at
which ATP can be resynthesised is also slower.
3 The LA system calls upon glycogen as a fuel which does not require a passive recovery to be
resynthesised so it can be used again as is the case with PC. As long as glycogen/glucose is
present and available to working muscles the LA system can utilize this and contribute to energy
production.
4 All three systems would be contributing to ATP production with PC being depleted slower than a
100 m sprint because the intensity would not be maximal from the outset of the race. It is likely
the anaerobic glycolysis/LA system would be contributing most to ATP production at this stage
with the aerobic system staring to really ‘crank up’ due to increased functioning of the
cardiovascular and respiratory systems. It must be recognized however that the aerobic system
needs 75 seconds when working maximally to take over from the two anaerobic energy systems
as the major ATP producer. Approximate contributions at the 40 second stage would be:
ATP-PC energy system – 5%
Anaerobic glycolysis / LA energy system – 55%
Aerobic energy system – 40%
5 The runner would not be working maximally for the duration of his/her event. Furthermore, the
cyclist would be able to take up and transport greater amounts of oxygen due to increased work
rates from the cardiovascular and respiratory systems. Differences would also occur because the
cyclist would be using fewer muscles than the runner who is totally weight bearing on the
running surface.
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4. 6 Even though the athlete is sprinting PC has not had a chance to rebuild itself and hence has no
contribution to the final burst of effort/sprint. The anaerobic glycolysis/LA system would
increase its contribution when compared to the previous distances when less effort was
required but this would only result is a maximum of 3 moles of ATP production. Because the
event has been going for between 3 mins and 3 ½ mins the aerobic system has had sufficient
time take over as the major supplier of ATP and will continue to do so even in the final sprint to
the finish line because it is capable of procuring 36 moles of ATP.
Thinking things through p. 141
1
Short interval training develops the ATP-PC system
Intermediate interval training develops the anaerobic glycolysis/LA system.
2 In most cases this would restrict repeated use of the ATP-PC system due to insufficient recovery
time to restore PC to pre-exercise levels. This would typically be done where game demands
called upon this type of recovery and where improvement in lactate tolerance and delayed LIP
are essential to being successful. The decreased rest period would increasingly activate the
aerobic energy system as well
3 An active recovery will facilitate H+ removal but will not adequately allow for PC to be
resynthesised.
4 Anaerobic training at or slightly above the LIP will increase the intensity performers can work at
before triggering it (this may take 9+ months). Additionally, anaerobic training will allow
performers to work at higher intensities for longer which will lead to earlier and increased
activation of the aerobic energy system.
Review questions
Multiple choice p. 143
1 C
2 B
3 D
4 D
Short answer p. 143–4
5 Fats take much longer than carbohydrates to break down and so the rate at which they produce
energy is slower. Carbohydrates do not require the same amount of oxygen as fats to produce
energy so more is available to working muscles.
6 a Three advantages an athlete has by being able to increase their LIP include:
Work at a higher intensity before starting to accumulate fatiguing H+ ions
Activate aerobic system at an earlier stage of performance and delay ‘anaerobic’ related
fatigue mechanisms
Allows performers to ‘save energy’ for later on i.e. can work aerobically whilst competitors
work anaerobically.
Produce more energy/ATP per gram of fuel
b There will be greater contribution from aerobic energy system.
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5. c Intermittent training/intermediate interval training will cause the anaerobic glycloysis system
to become more powerful. This will see an increase in glycogen stores and glycolytic enzymes
and most likely delay the point at which H+ ions will rapidly accumulate.
7 a By training – Increase muscle size/hypertrophy and thus provide a bigger storage site for PC or
by diet manipulation – Creatine supplementation
b This will allow the PC system to work as the major ATP producer for longer before the
anaerobic glycolysis/LA system takes over as the major ATP producer and the associated sharp
rise in metabolic by-products (especially H+).
8 ATP is resynthesised via the three energy systems and how all three systems work together to
provide energy, also known as the energy system interplay. Discussion must clearly demonstrate
all 3 systems are working to varying amounts based on intensity, duration and ability to refuel –
table 5.11 provides great examples.
9 Because the event does not start out at maximal intensity the ATP-PC system would last about
15–20 seconds before ATP is predominantly produced produced by the anaerobic glycolysis/LA
system. At the same time the aerobic system is increasing its contribution and takes over as the
predominant Atp producer around the three minute mark and continues to be the predominant
energy producer throughout the event. When the runners surge, or work at higher intensities
such as running uphill, there is increased contribution from the LA system but this still produces
one twentieth as much energy as the aerobic energy system. There are no opportunities to
replenish Pc throughout the race so its contribution to ATP production remains negligible from
about the 20–30 second stage of the race.
10 a 200 m = 0.2 litres/min or 200 ml/min = 20% 800 m = 2.0 litres/min = 65-70%
b 400 m – 30% aerobic 70% anaerobic, 1500 m – 70% aerobic 30% anaerobic
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