Sports Nutrition Principles
The Sports Nutrition Principles domain tests whether you can explain how energy systems, macronutrients, and fluid balance drive performance - and support recommendations with accepted numbers rather than gym folklore. Expect questions on substrate use, daily intake ranges, and hydration math.
Energy systems and fuel selection
- The phosphagen (ATP-PC) system dominates efforts under ~10 s; glycolysis covers roughly 10 s to 2 min; oxidative metabolism dominates beyond ~2–3 min. Intensity, not duration alone, sets the fuel mix.
- Fuel values: carbohydrate and protein 4 kcal/g, fat 9 kcal/g, alcohol 7 kcal/g.
Daily macronutrient ranges
- Carbohydrate scales with training load: 3–5 g/kg/day for light training, 5–7 g/kg for ~1 h/day, 6–10 g/kg for 1–3 h/day, and 8–12 g/kg for 4–6+ h/day.
- Protein: 1.2–2.0 g/kg/day, with ~1.6 g/kg common for strength athletes; 20–40 g per meal every 3–4 h, supplying roughly 2.5 g leucine.
- Fat: 20–35% of energy, kept at or above ~20% to supply essential fatty acids and fat-soluble vitamins.
Hydration
- Sweat rate = (pre-weight − post-weight + fluid consumed) ÷ hours; 1 kg ≈ 1 L.
- Drink 5–10 mL/kg in the 2–4 h before exercise; include 300–700 mg sodium per litre for sessions beyond ~2 h.
Worked example
A 70 kg athlete weighs 70.0 kg before and 69.0 kg after a 2 h session, drinking 500 mL. Sweat loss = 1.0 kg + 0.5 L = 1.5 L, so the rate is 750 mL/h. Replace 125–150% of the deficit over the next 2–4 h: about 1.9–2.25 L, using sodium-containing fluids.
Traps that cost marks
- Quoting carbohydrate as a percentage of energy when the question asks for g/kg.
- Forgetting to add fluid consumed to the body-weight change.
- Treating a sweat rate measured in cool conditions as fixed for a hot race.
- Using 9 kcal/g for protein.