Lesson 11 · What factors influence movement and performance?
What you eat decides which energy system can actually run
Lessons 9 and 10 analysed three pathways and named their fuels. This lesson asks the question that follows immediately and that the syllabus asks directly: where do those fuels come from, how much of each does an active person need, and what happens to the pathways when something is missing. The answer is more interesting than a food pyramid. One of these nutrients is stored in an amount that runs out in about ninety minutes of hard work. Another is so abundant that you could not exhaust it in a week, and is nonetheless useless above a certain intensity. And a third group is needed in milligrams, contributes no energy at all, and without it not one molecule of ATP gets made.
Two athletes train at the same club. One is a 1500 metre runner who trains for ninety minutes most days. The other is a shot putter who trains for the same ninety minutes, but whose actual efforts in that session add up to perhaps two minutes of maximal work.
They eat the same meals. One of them is eating badly for their sport, and it is not obvious which. Write down which one you think is worse off and why, then answer a harder question: the runner takes an iron supplement and says it gives them energy. Iron contains no kilojoules at all. Explain how a substance with no energy in it can make a genuine difference to how much energy someone can produce — or explain why you think the claim is nonsense.
- Explain the role of each macronutrient — carbohydrate, fat and protein — in supplying the three energy systems.
- Explain why intensity, not sport reputation, decides the fuel mix, and what that means for what each athlete should eat.
- Describe the macronutrient requirements of active people, and why they are expressed per kilogram of body mass rather than as a flat amount.
- Explain the role of micronutrients — iron, calcium, the B group vitamins, and antioxidant vitamins — in enabling the energy systems to function.
- Explain why a micronutrient deficiency reduces performance even though micronutrients supply no energy.
- Explain the role of water, and why it belongs in a lesson about energy production.
- Apply all of this to judge a real athlete's diet against the demands of their event rather than against a general rule.
- Macronutrient — a nutrient required in large amounts that supplies energy: carbohydrate, fat and protein.
- Micronutrient — a vitamin or mineral required in milligram or microgram amounts, supplying no energy but essential to the reactions that release it.
- Glycogen — the stored form of carbohydrate, held in muscle and liver, and the limiting fuel of prolonged high-intensity work.
- Glycaemic index — a ranking of how quickly a carbohydrate food raises blood glucose.
- Triglyceride — the stored form of fat, in adipose tissue and within the muscle fibre itself.
- Haemoglobin — the iron-containing protein of the red blood cell that carries oxygen, met in Lesson 4.
- Coenzyme — a small molecule, often derived from a vitamin, that an enzyme requires in order to work.
- Energy availability — the energy left for body function once the energy cost of training has been taken out of what was eaten.
Every energy system in Lessons 9 and 10 was described by its fuel. Nutrition is simply the supply chain for those fuels, and the three macronutrients are not interchangeable suppliers. They differ in how much energy they carry, how fast that energy can be released, how much of it the body will store, and whether the body has any other use for them.
| Carbohydrate | Fat | Protein | |
|---|---|---|---|
| Energy density | About 17 kilojoules per gram | About 37 kilojoules per gram | About 17 kilojoules per gram |
| Which systems it feeds | All three: glucose feeds the glycolytic system, and glucose and glycogen feed the aerobic system | The aerobic system only, as fatty acids | The aerobic system; protein can contribute a small, context-dependent amount during exercise |
| How much is stored | Small — roughly 90 minutes to 2 hours of hard exercise, as muscle and liver glycogen | Very large — enough for many hours, even in a lean athlete | No dedicated fuel store; amino acids for fuel can come from food or body protein |
| Its other job | The only fuel the brain can normally use, and the only one that can be broken down without oxygen | Insulation, organ protection, and the transport of the fat-soluble vitamins | Building and repairing muscle, enzymes, haemoglobin and antibodies — this is its real job |
Read the bottom row again, because it is the one that sorts the good answers from the ordinary ones. Protein is not a dedicated fuel store: its main role is structural, but some protein is oxidised during exercise. A 2025 review of adult endurance studies found a small average energy contribution, with protein oxidation rising with exercise intensity. This does not mean protein waits until carbohydrate stores are exhausted or that it replaces the need to match carbohydrate to training.
And read the storage row beside the energy-density row, because together they explain the central tension of sports nutrition. The fuel with the most energy in it is the one you can least afford to rely on at high intensity, and the fuel you run out of first is the one you cannot do without. Fat is the bigger tank; carbohydrate is the wider pipe.
Quick check: The main reason protein contributes very little energy during normal exercise is that:
Lesson 10 established the rule and this lesson spends it: as intensity rises, the proportion of energy taken from carbohydrate rises and the proportion taken from fat falls. At rest and at a gentle walk, fat supplies most of the energy. At around 65 per cent of maximum the two are roughly equal. Above about 85 per cent, carbohydrate supplies almost all of it, because fat cannot be broken down fast enough and needs more oxygen per unit of energy released.
That single relationship answers the Card 01 question. The 1500 metre runner works for long periods above the crossover point, so almost all of their energy comes from a store that holds about ninety minutes' worth. Their carbohydrate intake is not a preference; it is the thing that decides whether they can finish the session they have planned. The shot putter's efforts last two to six seconds each and are supplied by phosphocreatine, which is resynthesised between attempts; their total energy expenditure across a session is modest, and their nutritional priority is protein and total energy sufficient to support the muscle they are trying to build, not glycogen.
So neither athlete is wrong because their diet is unhealthy. They are wrong relative to their event. The same plate is well matched to one training week and poorly matched to the other, and the discriminator is the intensity and duration profile of the work — exactly the profile you built for your own sport in Lesson 10.
True or false: Because the proportion of energy supplied by fat is highest at low intensities, a low-intensity session always uses more total fat than a hard one.
Sports nutrition guidelines are almost never given as a number of grams. They are given per kilogram of body mass per day, and that convention carries a real idea: a 55 kilogram gymnast and a 110 kilogram forward have the same physiology and different amounts of it, so a flat recommendation would be simultaneously too much for one and too little for the other.
| Macronutrient | Light to moderate training | Heavy or prolonged endurance training | Why the range moves |
|---|---|---|---|
| Carbohydrate | Around 3 to 5 g per kg per day | Around 6 to 10 g per kg per day, and higher again in very long events | Tracks the volume of work done above the crossover point, because that is what empties glycogen |
| Protein | Around 1.2 g per kg per day | Around 1.4 to 2.0 g per kg per day, at the upper end for heavy resistance training | Tracks how much tissue is being repaired and built, not how much energy is being used |
| Fat | Around 20 to 35 per cent of total energy intake, and rarely below 20 per cent | Expressed as a share rather than per kilogram, because its main constraint is a floor, not a target | |
Three features of that table are examinable and are routinely missed.
Carbohydrate scales with training load, not with body size alone. The same athlete needs a different intake in a heavy week and a taper week, which is why a single number for a person is meaningless without a training context.
Protein has a ceiling of usefulness. Intake beyond roughly 2 grams per kilogram is not stored as extra muscle; the surplus is used as energy or stored as fat, and the amino group is excreted. More protein does not produce more muscle in the way advertising implies — the stimulus for muscle growth is the training, and protein is the material it requires.
Fat has a minimum. Cutting fat too low compromises absorption of the fat-soluble vitamins A, D, E and K and interferes with hormone production. A very low fat intake is a recognised route into low energy availability, where total intake is insufficient once the cost of training is taken out — with consequences for bone density, immune function and, in menstruating athletes, for menstrual function.
Match each nutrient to the reason an active person needs it in the amount they do.
- Carbohydrate
- Protein
- Fat
- Water
- Scales with the volume of work done at high intensity, because that is what depletes the store
- Scales with the amount of tissue being repaired and built, and stops being useful past about 2 g per kg
- Has a floor rather than a target, because too little impairs vitamin absorption and hormone production
- Supplies no energy at all, but a small deficit reduces blood volume and raises core temperature
This is the half of the dot point that students skip, and it is where the second Card 01 question is answered. A micronutrient supplies no kilojoules. It contributes to energy production by being part of the machinery that releases energy from the macronutrients, or part of the system that delivers the oxygen the machinery needs. Take the part away and the fuel is still there, unusable.
| Micronutrient | Role in energy production | What a deficiency does to performance |
|---|---|---|
| Iron | The core of haemoglobin in red blood cells and of myoglobin in muscle, so it is what oxygen binds to on the way to the mitochondria | Less oxygen delivered, so the aerobic system is capped lower; fatigue at intensities that were previously comfortable. The single most common deficiency in athletes, particularly in adolescent and menstruating athletes |
| B group vitamins (B1, B2, B3, B6, B12) | Coenzymes in the reactions of glycolysis and of aerobic metabolism — the enzymes cannot work without them | Reduced rate of ATP resynthesis from fuel that is present and abundant |
| Calcium | Required for the muscle contraction itself, and for bone mineral density | Impaired contraction, and over time a raised risk of stress fracture, which removes the athlete from training altogether |
| Vitamin D | Governs calcium absorption, and contributes to muscle function | Undermines calcium intake however good it is, so bone and muscle suffer despite an adequate diet |
| Antioxidant vitamins (C and E) | Limit the damage done by the free radicals produced during heavy aerobic metabolism, and vitamin C also aids iron absorption | Slower recovery, and poorer absorption of the iron that was eaten |
| Sodium and potassium | Electrolytes that carry the nerve impulse and trigger contraction, lost in sweat | Cramping, impaired nerve conduction, and in extreme cases dangerous disturbance of fluid balance |
Notice the shape of the iron row, because it is the model answer to the Card 01 question. Iron contains no energy. What it does is carry oxygen. Without oxygen delivery the aerobic system — the one system that can run indefinitely — is throttled, and the athlete has to take a larger share of their energy anaerobically at any given pace, which brings forward fatigue. So the supplement does not give energy; it removes a restriction on the energy the athlete could already have produced. That distinction is worth a mark whenever it appears.
One important qualification, and it is the reason the claim on the tin is still misleading. Correcting a deficiency improves performance. Exceeding a requirement does not. An athlete with normal iron stores who takes iron gains nothing, and in excess iron is genuinely harmful. The same is true of most micronutrients, which is why a blood test rather than a slogan is what justifies a supplement.
Two truths and a lie. Which statement is false?
Water supplies no energy, is not a macronutrient and is not a micronutrient, and it is nonetheless the nutrient whose shortage degrades performance fastest. Lesson 10 named dehydration and rising body temperature as causes of aerobic fatigue; this card supplies the mechanism.
Sweat is drawn from the body's water, and a large share of that comes from the blood plasma. Losing water therefore reduces blood volume, and a smaller volume of blood has three immediate consequences. Stroke volume falls, so the heart must beat faster to deliver the same amount of oxygen — the rise in heart rate at a fixed workload that you will measure in Lesson 14. Less blood is available to send to the skin, so heat is removed more slowly and core temperature rises. And the same reduced volume must supply both the working muscle and the skin, which are now competing.
A fluid loss of about 2 per cent of body mass — 1.4 kilograms in a 70 kilogram athlete, which is an ordinary summer training session — is enough to produce a measurable fall in endurance performance and in the quality of decision-making. That second effect connects straight back to Lesson 7: the nervous system degrades before the muscles do, so the first visible sign of dehydration in a team sport is usually a skill error, not a slow run.
Fill the gaps. Type one word in each box.
Nutrients required in large amounts that supply energy are called . The stored form of carbohydrate in muscle and liver is . The mineral at the centre of haemoglobin, and therefore the one that limits oxygen delivery when it is deficient, is .
Text description
- Two linked parts, one above the other.
- Above, the share of energy supplied by fat and by carbohydrate plotted against exercise intensity from rest to maximum: the fat line starts high and falls, the carbohydrate line starts low and rises, they cross at about sixty-five per cent of maximum, and the region above eighty-five per cent is shaded to show that carbohydrate supplies almost all of the energy there.
- Below, a supply chain running top to bottom: the three macronutrients feed the three energy systems, which depend on the micronutrients and water listed beneath them: iron for oxygen delivery, B group vitamins as coenzymes, calcium for contraction, and water for blood volume.
Activities · put the method to work
Use your own body mass and the sport profile you built in Lesson 10. If you do not train, use a hypothetical 70 kilogram athlete training six hours a week.
Set the target. Using the Card 06 table, work out the carbohydrate and protein ranges in grams per day for your body mass, at the training load you actually do. State which column you chose and why.
Record one day. Write down everything eaten and drunk in one ordinary training day. Do not improve it while you write it; an audit of an invented day measures nothing.
Classify, do not count. For each item, name the dominant macronutrient and which energy system it mainly supplies. You are not calculating kilojoules; you are asking whether the fuel matches the pathway the training uses.
Find the micronutrient risk. Identify one micronutrient from Card 07 that this day supplies poorly, name the mechanism by which a shortage of it would show up in training, and say what an ordinary food change would fix it.
Finish with one sentence of judgement: is this diet mismatched to the training, adequate, or better than the training requires? All three are possible answers and only one of them is the one people expect.
Odd one out. Three of these describe a nutrient contributing to energy production. Which one does not?
Each of the following is something widely said. For each: decide whether it is right, wrong, or right for the wrong reason; name the mechanism that settles it; and write what you would say to the person instead.
"Carbohydrate makes you fat, so athletes should cut it."
"I have a protein shake after every session because that is what builds the muscle."
"Sports drinks are just sugar water, so plain water is always the better choice."
"She is a vegetarian distance runner, so she will be iron deficient."
For at least one of the four, you should end up arguing that the claim is right for the wrong reason. Identifying which one, and saying precisely where the reasoning fails while the conclusion survives, is the part of this activity that is worth marks in an exam.
Explain the role nutrition plays in enabling the energy systems to function efficiently, referring to both macronutrient and micronutrient requirements of active people.
Explain means make the relationship clear by giving how and why, not what. The question names macronutrients and micronutrients separately, so an answer that treats only the first half caps itself at about three marks however good it is.
Plan: macronutrients as the fuels, matched to systems; intensity as the thing that decides the mix; requirements per kilogram scaled to training load; then micronutrients as the machinery rather than the fuel, with iron as the worked case; close on deficiency versus excess.
Carbohydrate is stored as muscle and liver glycogen and is the only macronutrient that can be broken down without oxygen, so it supplies the glycolytic system and a rising share of the aerobic system as intensity increases. Fat is stored in far greater quantity and supplies the aerobic system only, and requires more oxygen per unit of energy released, so it cannot contribute meaningfully above about 85 per cent of maximum. Protein is mainly structural, but it can contribute a small amount of energy during exercise; this contribution is not limited to carbohydrate depletion.
Requirements are expressed per kilogram of body mass and scaled to training load: roughly 3 to 5 grams of carbohydrate per kilogram per day for light training and 6 to 10 for heavy endurance training, and roughly 1.2 to 2.0 grams of protein per kilogram. Carbohydrate scales with the volume of high-intensity work, because that is what empties the glycogen store, while protein scales with the tissue being repaired and ceases to be useful beyond about 2 grams per kilogram.
Nutrition supplies the energy systems in two distinct ways, and an efficient system requires both. The macronutrients are the fuels themselves. Carbohydrate, stored as glycogen in muscle and liver, is the only fuel that can be broken down without oxygen, so it supplies the glycolytic system entirely and supplies a rising proportion of aerobic energy as intensity increases; because the store is small, holding roughly 90 minutes to two hours of hard work, it is also the fuel that limits prolonged high-intensity exercise. Fat, stored as triglyceride in adipose tissue and within the muscle, carries about 37 kilojoules per gram against carbohydrate's 17 and is available in effectively unlimited quantity, but it can be used only aerobically and requires more oxygen per unit of energy, so its contribution falls as intensity rises and is negligible above about 85 per cent of maximum. Protein is mainly structural material for muscle, enzymes and haemoglobin rather than a dedicated fuel store. It can also be oxidised during exercise, usually contributing a small share of energy; a 2025 review of adult endurance studies found that this share increased with exercise intensity, without requiring carbohydrate stores to be exhausted. This does not make protein a substitute for appropriate carbohydrate intake. Requirements are therefore expressed per kilogram of body mass and scaled to training load, since the demand is set by the work done rather than by the sport's name: approximately 3 to 5 grams of carbohydrate per kilogram per day for light to moderate training and 6 to 10 for heavy endurance training, approximately 1.2 to 2.0 grams of protein per kilogram depending on how much tissue is being repaired, and fat at 20 to 35 per cent of total energy with a floor below which absorption of fat-soluble vitamins and hormone production are compromised. The micronutrients supply no energy at all, and enable the systems in the second way: they are the machinery that releases the energy and delivers the oxygen the machinery needs. Iron forms the centre of haemoglobin and myoglobin, so a deficiency reduces oxygen delivery and lowers the intensity at which the aerobic system can predominate, forcing a greater anaerobic contribution at any given pace and bringing fatigue forward. The B group vitamins act as coenzymes in glycolysis and aerobic metabolism, so a deficiency slows ATP resynthesis from fuel that is present and abundant. Calcium is required for the muscle contraction itself and for bone density, and vitamin D governs its absorption. Water, though not a nutrient that supplies energy, maintains the plasma volume on which stroke volume and heat loss depend, and a loss of only 2 per cent of body mass measurably reduces endurance performance and decision quality. Critically, correcting a deficiency improves performance while exceeding a requirement does not, and may be harmful, which is why supplementation is justified by a measured deficiency rather than by a general belief that more of an essential nutrient must be better.
A 60 kilogram netball player and a 95 kilogram rower follow the same diet. Explain why the same intake can be adequate for one athlete and inadequate for the other, and explain how a deficiency of a nutrient that contains no energy could reduce the performance of either.
There are two, and an answer that finds only one reads as half-finished. The first is body mass, because requirements are per kilogram. The second, and the more interesting, is the activity profile: a rowing session is prolonged work well above the crossover point, while netball is intermittent, so the two athletes deplete glycogen at very different rates even before their mass is considered.
Plan: mass first, briefly; activity profile second, with the crossover; then compute both carbohydrate targets to make the gap concrete; then the micronutrient half, using iron.
At 6 to 10 grams of carbohydrate per kilogram for heavy endurance training, the 95 kilogram rower requires roughly 570 to 950 grams per day. At 3 to 5 grams per kilogram, appropriate to a mainly intermittent load, the 60 kilogram netball player requires roughly 180 to 300 grams. An intake adequate for the second is therefore less than half of the lower bound for the first.
Iron contains no energy, but it is the centre of the haemoglobin molecule that carries oxygen in the blood and of myoglobin in the muscle. A deficiency therefore reduces the amount of oxygen that reaches the mitochondria, which caps the rate at which the aerobic system can resynthesise ATP. The athlete must take a larger share of their energy from the glycolytic system at any given pace, accumulating hydrogen ions sooner, so fatigue appears at an intensity that was previously sustainable.
The same intake can be adequate for one of these athletes and inadequate for the other for two independent reasons. The first is body mass: macronutrient requirements are expressed per kilogram precisely because a larger athlete has more muscle to fuel and repair, so the 95 kilogram rower's requirement exceeds the 60 kilogram netballer's by more than half again at any given intake per kilogram. The second, and the more important, is the activity profile, because the intake per kilogram is itself set by the training load. Rowing training is prolonged work sustained well above the crossover point at which carbohydrate overtakes fat as the dominant fuel, so it depletes muscle and liver glycogen heavily and repeatedly, placing the rower in the heavy endurance band of roughly 6 to 10 grams of carbohydrate per kilogram per day, or about 570 to 950 grams. Netball is intermittent, consisting of brief high-intensity efforts separated by low-intensity periods, so although its efforts are hard, its total glycogen cost is far lower and it sits in the 3 to 5 gram band, or about 180 to 300 grams. An intake that meets the netballer's requirement therefore supplies less than a third of the rower's, and the rower would begin sessions with partly depleted glycogen, be unable to complete the planned work, and over successive days accumulate fatigue. Protein can also be oxidised during exercise, but it remains a small, context-dependent contribution rather than a reserve that is used only after glycogen is depleted. The netballer's greater need is proportionally for protein and for total energy sufficient to recover between sessions, not for the rower's carbohydrate volume. The second half of the question concerns a nutrient with no energy content, and iron is the clearest case. Iron is the centre of the haemoglobin molecule that transports oxygen in the blood, and of myoglobin within the muscle fibre, so a deficiency reduces the oxygen delivered to the mitochondria. Since the aerobic system cannot resynthesise ATP faster than oxygen arrives, its ceiling falls, and the athlete must take a greater share of their energy from the glycolytic system at any given pace. Hydrogen ions accumulate sooner, muscle pH falls, and fatigue appears at an intensity that was previously comfortable, so the athlete experiences a genuine loss of endurance performance caused by a nutrient that supplied no energy in the first place. The same logic applies to the B group vitamins, which act as coenzymes in the pathways themselves, and to water, whose loss reduces plasma volume and therefore stroke volume. In each case the nutrient is not the fuel; it is part of the machinery that makes the fuel usable, which is why correcting a genuine deficiency improves performance while exceeding a requirement does not.
Multiple choice · 5 questions
MC 1. The only macronutrient that can be broken down to resynthesise ATP without oxygen is:
- A. fat
- B. protein
- C. carbohydrate
- D. all three, at different rates
MC 2. Sports nutrition requirements are usually expressed per kilogram of body mass because:
- A. larger athletes absorb nutrients less efficiently than smaller ones
- B. a flat recommendation would over-supply a small athlete and under-supply a large one
- C. body mass determines which energy system an athlete uses
- D. it allows fat to be expressed in grams rather than as a percentage
MC 3. An endurance athlete with an iron deficiency fatigues earlier than before mainly because:
- A. iron is a fuel that the aerobic system has run short of
- B. less oxygen reaches the mitochondria, so more energy must be supplied anaerobically at the same pace
- C. iron is required to store glycogen in the muscle
- D. iron deficiency reduces the number of kilojoules absorbed from food
MC 4. Protein intake above roughly 2 grams per kilogram per day in a trained athlete:
- A. produces a proportional further increase in muscle mass
- B. is stored in the muscle as a protein reserve for later use
- C. converts directly into glycogen for use by the glycolytic system
- D. provides no further benefit, and the surplus is used for energy or stored as fat
MC 5. A fluid loss of about 2 per cent of body mass reduces endurance performance principally because:
- A. the muscles run short of the water needed to break down glycogen
- B. plasma volume falls, so stroke volume falls and less blood reaches both muscle and skin
- C. the loss of water removes most of the body's stored carbohydrate
- D. sweat removes the fat-soluble vitamins from the body
Short answer · exam style
SA 1. Remember Band 3 Outline the role of carbohydrate, fat and protein in supplying energy for physical activity. (3 marks)
SA 2. Understand Band 5 Explain how a deficiency in a micronutrient can reduce performance even though micronutrients supply no energy. Refer to at least two different micronutrients. (5 marks)
SA 3. Analyse Band 6 Explain why two athletes of similar body mass, one a marathon runner and one a sprinter, require very different macronutrient intakes. (6 marks)
📖 Comprehensive answers (click to reveal)
Multiple choice: 1 → C. 2 → B. 3 → B. 4 → D. 5 → B.
Activity 1 guidance: The step that does the teaching is step 3, and the instruction not to count kilojoules is deliberate. Students who total energy end up with a number they cannot interpret; students who classify by dominant macronutrient and by system supplied end up with a structural answer — typically that the day is adequate in protein, low in carbohydrate relative to a heavy training load, and adequate in total energy only because fat intake is high. The most common genuine finding in an adolescent athlete's day is that breakfast and the post-training window are the two thin points, and that both fall immediately before or after the largest glycogen cost of the day. On step 4, iron and calcium are the two micronutrients most often under-supplied, and the mechanism required is the one from Card 07, not the word "important". Note the judgement sentence deliberately offers three verdicts: a diet that exceeds what the training requires is a real and common finding in a student who trains twice a week, and saying so is a better answer than manufacturing a deficiency.
Activity 2 guidance: Claim 1 is wrong, and the mechanism that settles it is that any macronutrient in excess of energy requirements contributes to fat gain, while carbohydrate specifically is the fuel that high-intensity training cannot proceed without; an athlete who cuts it trains worse and therefore adapts less. Claim 2 is right for the wrong reason, and this is the one the activity is built around. Protein after training is genuinely useful, but the stimulus for muscle growth is the training itself, and protein is the material rather than the trigger; an athlete who believes the shake is doing the building will take a second shake instead of a harder session. It is also worth noting that total daily protein matters more than the timing of any single serve. Claim 3 is wrong as stated but contains a real point: for sessions under about an hour, water is sufficient and a sports drink adds unnecessary energy; for prolonged or very hot sessions, the carbohydrate and sodium in a sports drink are exactly what is required, and sodium also aids fluid retention. The error is treating a duration-dependent question as though it had one answer. Claim 4 is wrong as a prediction about an individual, though it identifies a real elevated risk: vegetarian diets supply non-haem iron, which is less readily absorbed, and distance running raises iron losses, so the risk is genuinely higher — but risk is not diagnosis, vitamin C taken with the meal substantially improves non-haem absorption, and the only thing that settles an individual case is a blood test.
SA 1 (3 marks): Carbohydrate — stored as muscle and liver glycogen, the only fuel usable without oxygen, supplying the glycolytic system and an increasing share of aerobic energy as intensity rises, with a limited store [1]. Fat — stored as triglyceride in far greater quantity at about 37 kilojoules per gram, usable only aerobically and only at low to moderate intensity because its breakdown is slower and requires more oxygen [1]. Protein — primarily structural, for building and repairing tissue; it can contribute a small amount of energy during exercise, and this contribution is not restricted to severe carbohydrate depletion [1]. An answer that lists all three as fuels without distinguishing protein's structural role caps at 2.
SA 2 (5 marks): States that micronutrients supply no energy but form part of the machinery that releases it or delivers the oxygen it requires [1]. First micronutrient with a mechanism — for example iron as the centre of haemoglobin and myoglobin, so deficiency reduces oxygen delivery [1]. The consequence traced — the aerobic ceiling falls, so a greater anaerobic contribution is required at the same pace and fatigue arrives earlier [1]. Second micronutrient with a different mechanism — for example B group vitamins as coenzymes, so ATP resynthesis slows despite abundant fuel; or calcium, required for the contraction itself and for bone density [1]. The deficiency-versus-excess distinction — correcting a deficiency improves performance, exceeding a requirement does not and may be harmful [1]. Two micronutrients sharing one mechanism earns only one of the two mechanism marks.
SA 3 (6 marks): The marathon runner's profile described — prolonged continuous work above the crossover point, predominantly aerobic, for two hours or more [1]. The sprinter's profile described — efforts of around ten seconds supplied by ATP-PCr, with long recoveries and a modest total energy cost [1]. The consequence for glycogen — the runner depletes muscle and liver glycogen heavily and repeatedly, the sprinter barely touches it [1]. Carbohydrate requirements quantified — roughly 6 to 10 grams per kilogram per day for the runner against 3 to 5 for the sprinter, with the reason being training load rather than body mass, since the masses are similar [1]. Protein requirements compared — the sprinter's is at the upper end of the range because of heavy resistance training and the muscle mass being built and maintained, and is proportionally a larger share of their intake [1]. The consequence of swapping diets — the runner on the sprinter's intake begins sessions with less carbohydrate available for the planned endurance work, which may limit the ability to complete it; the sprinter on the runner's intake takes in carbohydrate surplus to requirements with no performance benefit and possibly unwanted mass gain [1]. Note that the question controls for body mass deliberately: an answer that explains the difference by size alone has answered a different question and earns at most 2.
Two kinds of nutrient, two completely different jobs. The macronutrients are the fuel: carbohydrate for the glycolytic system and for a rising share of aerobic energy, fat for the aerobic system alone, protein mainly for structure, while also contributing a small amount of exercise energy. The micronutrients are the machinery: iron carrying the oxygen, the B group vitamins acting as coenzymes, calcium producing the contraction, vitamin D governing calcium's absorption. Take away a fuel and the pathway slows. Take away a part of the machinery and the fuel becomes unusable.
Intensity decides the mix, and that is why requirements are written per kilogram and per training load. Fat dominates at rest, carbohydrate dominates above about 65 per cent of maximum and supplies almost everything above 85 per cent. So the athlete who works hardest for longest has the largest carbohydrate requirement, regardless of what their sport is called — roughly 6 to 10 grams per kilogram per day against 3 to 5 for light training, with protein at 1.2 to 2.0 and a ceiling of usefulness at the top of that range.
The sentence to be able to write. A nutrient with no kilojoules in it can still change performance, because performance is limited by the rate at which ATP can be resynthesised, and that rate depends on oxygen delivery and enzyme function as much as it depends on fuel. Iron is the worked case: deficiency lowers the aerobic ceiling, forces a greater anaerobic contribution at the same pace, and brings fatigue forward. And the qualification that shows you understood it: correcting a deficiency helps, exceeding a requirement does not.
Lesson 12 turns from what fuels the systems to what changes them. It compares aerobic and anaerobic training for individuals and for group sports, including how a program is differentiated for different people and what the contemporary methods of training actually are.
Mark lesson as complete
Tick when you've finished the practice and review.