2.2 Explain the role nutrition plays in enabling the energy systems to function efficiently, including macronutrient and micronutrient requirements of active people

1. Nutrients

1.1 Carbohydrate

Carbohydrate is the most important fuel for moderate to high intensity activity because it can support a faster rate of ATP resynthesis than fat. Dietary carbohydrate is digested into glucose, which can be stored as glycogen in skeletal muscle and the liver. Total glycogen storage is limited, with typical values often quoted as about 400 g stored across skeletal muscle and about 100 g stored in the liver. When glycogen falls substantially, maintaining moderate to high intensity output becomes harder, so performance drops even if skill and motivation remain high.

Carbohydrate supports efficient energy system function in two key ways. First, it is the primary fuel for the glycolytic system, which provides rapid ATP without relying on oxygen during high intensity efforts. Second, it contributes strongly to the aerobic system, particularly as intensity increases, because carbohydrate can be oxidised at a higher rate than fat.

Fuel contribution shifts with intensity. At rest and during very low intensity activity, the body typically relies more on fat than carbohydrate for ATP production, with fat contributing about two-thirds of energy and carbohydrate about one-third. As intensity rises, reliance shifts progressively towards carbohydrate because it can meet higher ATP demand.

Example: If you begin a high-intensity training session with low muscle glycogen, the glycolytic system cannot sustain repeated sprints as well. Sprint quality drops sooner, even if skill and motivation are unchanged.

Carbohydrate strategies can further improve efficiency by matching glucose availability to the task. Glycaemic index (GI) describes how quickly a carbohydrate food raises blood glucose. In performance contexts, higher GI choices are more useful when rapid glucose availability is needed (for example, immediately before, during, or soon after hard training), while lower GI choices are more useful when steadier fuel availability is needed across a longer session.

Example: Pre-game snack before repeated sprints: white bread with honey (higher GI) versus pre-long run meal: oats with fruit (lower GI).

Carbohydrate loading is a short-term strategy used before endurance events to maximise muscle glycogen stores. It is most relevant when events last longer than about 90 minutes and glycogen depletion is a key limiter. It typically involves increasing carbohydrate intake for 1–4 days while reducing training load so glycogen stores can be maximised.

Example: Before a long-distance running event, increasing carbohydrate intake across the final 48 hours can delay late-race fatigue because higher starting glycogen sustains carbohydrate-supported ATP production.

1.2 Protein

Protein supports efficient energy system function mainly by improving recovery and adaptation, not by directly fuelling most exercise. Protein provides amino acids used to repair training-related muscle damage, support growth and maintenance of lean mass, and produce enzymes and transport proteins involved in metabolism. This matters because better recovery and adaptation improves the body’s capacity to repeat high quality training, which supports stronger energy system performance over time.

Protein can also contribute to ATP production, but usually only to a small extent. Under normal conditions, protein often contributes around 5–10% of ATP production. This contribution becomes more relevant when exercise is very prolonged, when glycogen is low due to inadequate carbohydrate intake, or when total energy intake is insufficient for the training load. Increased reliance on protein for energy is usually a sign that fuelling is less efficient, because amino acids are being diverted away from repair and adaptation.

Example: An endurance athlete who chronically under-eats carbohydrate during a heavy training block may experience poorer recovery and increasing fatigue because more amino acids are used for energy rather than tissue repair.

1.3 Fats

Fats provide fatty acids, a major fuel source for lower intensity and longer duration activity where the aerobic system dominates. Fat oxidation supports ATP production when intensity allows enough oxygen delivery and time for the slower metabolic pathway to meet demand. This helps spare glycogen during sustained exercise, which can delay fatigue when duration is long.

Fat is a concentrated energy source. It provides about 37 kJ per gram, compared with about 17 kJ per gram for carbohydrate and protein. This makes it useful for meeting high energy demands, but it cannot supply ATP quickly enough to replace carbohydrate during maximal sprinting or heavy lifts.

Fats also support efficient performance indirectly by enabling absorption of fat-soluble vitamins (A, D, E, K), supporting hormone production, and contributing to cell membrane structure.

Example: A long, steady cycling session draws heavily on fat oxidation, but sustained high-intensity surges during the ride (for example a climb or sprint finish) still depend on carbohydrate for faster ATP delivery.

1.4 Micronutrients

Micronutrients are vitamins and minerals needed in small amounts, but they are essential for energy system efficiency because they support the chemical reactions that allow the body to turn carbohydrate and fat into usable ATP and to deliver oxygen to working muscles. Vitamins are organic compounds made by plants and animals. Minerals are inorganic elements from soil and water. The body needs both for structure and regulation.

For active people, key micronutrients include B-group vitamins (coenzymes in energy metabolism), iron (for haemoglobin and myoglobin, supporting oxygen transport for aerobic ATP production), calcium and vitamin D (muscle contraction and bone health), and electrolytes such as sodium, potassium, and magnesium (fluid balance and nerve signalling). Even mild deficiencies can increase fatigue and reduce performance and recovery, so a varied diet with plenty of whole foods is important to meet needs, especially during heavy training or when food intake is restricted.

1.5 Hydration’s role in nutrition

Hydration supports energy system efficiency by maintaining blood volume, supporting thermoregulation, and enabling normal metabolic reactions. When fluid levels fall, cardiovascular strain rises and exercise becomes less efficient at the same workload because oxygen and nutrient delivery to muscles is reduced and cooling becomes less effective.

Sweating is essential for temperature control, but it causes fluid and electrolyte loss. In moderate conditions, training can result in fluid losses of around 1 litre per hour, and more in heat. As dehydration increases, fatigue rises, perceived exertion increases, and the ability to sustain intensity declines.

Example: In hot conditions, a pace that is normally sustainable can feel harder because blood is being shared between working muscles and skin for cooling.

2. Nutritional requirements of active people

Active people require the same categories of nutrients as everyone else, but they often need different amounts, timing, and distribution to support training load, recovery, and competition demands. Efficient energy system function depends on meeting both macronutrient and micronutrient requirements, alongside adequate hydration.

2.1 Macronutrient requirements of active people

Macronutrient requirements vary with training volume, intensity, and whether the activity is predominantly anaerobic or aerobic.

Carbohydrate needs typically rise as training load increases. Practical daily targets are often expressed relative to body mass:

• 3–5 g/kg/day for lighter training or skill-based sessions
• 5–7 g/kg/day for moderate training (around 1 hour per day)
• 6–10 g/kg/day for high endurance training loads (1–3 hours per day)
• 8–12 g/kg/day for very high training loads (>4–5 hours per day)

Protein requirements are higher than sedentary needs because training increases muscle remodelling and recovery demands. Daily targets commonly used in sport include:

• 1.2–1.6 g/kg/day for many endurance athletes
• 1.6–2.0 g/kg/day for strength and power athletes

Fat intake is commonly kept within healthy guideline ranges while ensuring adequate total energy intake and fat-soluble vitamin absorption. Many active people aim for fat intakes broadly around 20–35% of total energy intake, prioritising unsaturated fat sources.

Example: A netball mid-courter benefits from adequate carbohydrate intake in the 24–48 hours before competition to support repeated accelerations and jumps across four quarters.

2.2 Micronutrient requirements of active people

Micronutrients do not provide energy (kilojoules), but they are essential for efficient ATP production because they support metabolic reactions, oxygen transport, nerve signalling, and muscle contraction. Small deficiencies can reduce performance even when macronutrient intake appears adequate.

B-group vitamins support energy metabolism by acting as coenzymes in pathways that convert carbohydrate and fat into ATP. Vitamin B12 and folate also support red blood cell production, which indirectly supports aerobic performance through oxygen delivery.

Iron is critical for oxygen transport as a component of haemoglobin (blood) and myoglobin (muscle). Low iron status reduces oxygen delivery, lowering aerobic ATP production and increasing fatigue. This is particularly relevant for athletes who menstruate, do high-volume endurance training, or restrict red meat without careful planning. Vitamin C improves absorption from plant sources, while large amounts of tea or coffee close to meals can reduce absorption for some people.

Calcium supports muscle contraction and bone strength. Vitamin D supports calcium absorption and contributes to muscle and immune function. Low vitamin D is more likely with limited safe sun exposure, winter training, or largely indoor training.

Electrolytes (especially sodium, potassium, and magnesium) support fluid balance and neuromuscular function. Sodium is the main electrolyte lost in sweat and supports fluid retention and nerve impulses.

Antioxidants (for example vitamins C and E, and minerals such as selenium and zinc) support cell protection, immune function, and recovery. A varied intake of colourful fruits and vegetables usually provides adequate antioxidant support, while high-dose supplementation is not a reliable performance enhancer and can be harmful in excess.

Example: Two athletes consume similar carbohydrate amounts, but one has low iron stores. Despite adequate fuelling, aerobic performance and recovery between efforts decline because oxygen delivery is limited.

2.3 Predominantly anaerobic versus predominantly aerobic activities

Nutritional priorities change depending on which energy system demands dominate.

Predominantly anaerobic activities involve high intensity, short duration, and repeated bursts, relying heavily on the ATP-PCr and glycolytic systems. Efficient performance depends on strong carbohydrate availability to support rapid ATP resynthesis, alongside adequate protein to support repair and adaptation from high-force work. Hydration still matters because dehydration reduces power output and increases fatigue, especially in Australian heat.

Example: An NRL forward needs carbohydrate availability to repeat short explosive efforts across a match, alongside adequate protein to recover from collisions and strength training.

Predominantly aerobic activities involve sustained effort where the aerobic system dominates. Both carbohydrate and fat contribute, but carbohydrate remains critical as intensity rises and as glycogen becomes limiting. Efficient endurance performance depends on high carbohydrate availability across training days, adequate total energy intake, and attention to hydration and key micronutrients that support oxygen transport, particularly iron.

Example: A triathlete who starts with full glycogen stores and maintains planned fuelling and hydration is less likely to experience a late-stage drop in pace as glycogen becomes limiting.

3. When to eat and drink

3.1 Food

Nutrient timing can improve energy system efficiency by ensuring fuel is available when ATP demand is highest and by accelerating recovery so energy systems can perform again soon.

Pre-exercise fuelling commonly aims to maximise glycogen and maintain comfort: a higher carbohydrate meal 3–4 hours before, a small carbohydrate snack 1–2 hours before if needed, and starting exercise well-hydrated.

Fuelling during exercise becomes more important as duration increases. For exercise longer than about 60 minutes, common guidance is 30–60 g carbohydrate per hour, taken regularly, with some endurance athletes consuming up to 90 g per hour in longer events where tolerated.

Post-exercise recovery fuelling supports rapid restoration and repair. A common target after demanding sessions is 1.0–1.2 g/kg carbohydrate in the first hour when rapid recovery is needed, plus 20–25 g protein soon after exercise. Rehydration is often guided by replacing about 150% of fluid lost, and including sodium when appropriate.

Example: After intervals or a long match, consuming carbohydrate plus protein soon after finishing supports faster glycogen restoration and muscle repair, improving readiness for the next session.

3.2 Drink

Hydration strategies are most effective when adjusted for conditions and sweat rate. Typical guidelines include about 500 mL in the 2 hours before exercise, roughly 400–800 mL per hour during exercise (when practical), and around 1.25–1.5 litres of fluid for every 1 kg of body mass lost after exercise. Including sodium can support fluid retention and reduce risk of hyponatraemia when large volumes of plain water are consumed during prolonged exercise.