Nutrition and hydration for activity
Physical Education · Key Stage 3 · The School
Fuel
CARBOHYDRATE is the main fuel for moderate and hard activity, stored in muscles and liver as glycogen; it runs out, which is what athletes mean by hitting the wall. FAT fuels long low-intensity activity and is effectively unlimited. PROTEIN is mainly for repair and adaptation rather than fuel, which is why eating more of it does not directly give more energy.
Water
Losing even one to two per cent of body mass as sweat measurably reduces performance and raises perceived effort; larger losses affect concentration and judgement, and become dangerous in heat. Thirst lags behind need, so drinking to thirst alone is a poor guide during long activity. Drinking far too much water is also harmful, which is why guidance is about steady modest amounts.
Judging a claim
Sports drinks, gels, bars and supplements are marketed with claims of varying quality. Useful questions: what does it actually contain, is there evidence in people doing this activity at this level, and would ordinary food do the same job more cheaply? For most school-age activity, ordinary meals and water cover the requirement, and a coach or a registered dietitian is the right person to ask.
A bottle claims it "fuels performance and replaces vital electrolytes". Check the context. For a 45-minute PE lesson: your glycogen stores are nowhere near empty and you have lost little salt, so water does the job and the sugar is surplus. For a two-hour match in heat: carbohydrate and sodium genuinely help maintain performance. The claim is not false — it is true for a situation you are probably not in.