Fuelling Long Sessions and Races

Carbohydrate, fluid and sodium, in the amounts your gut can actually handle on the day.

What this is

Fuelling is the highest-yield unforced error in amateur endurance sport. Most people under-fuel long events, blame their fitness, and train harder — when the problem was that the last hour ran out of carbohydrate.

The framework is simple: carbohydrate scaled to duration, fluid guided mostly by thirst, sodium when sweat losses are high, caffeine timed if you use it. The hard part isn't the numbers; it's practising them until your gut cooperates.

What the evidence says

  • Carbohydrate intake improves performance in prolonged exercise

    Gold· human data

    One of the most established findings in sports nutrition, with requirements scaling by duration and intensity.

  • Around 90 g per hour of mixed carbohydrate for long events

    Gold· human data

    Established via the multiple-transportable-carbohydrate research for events beyond about two and a half hours, subject to gut tolerance.

  • Gut training improves tolerance

    Silver· human data

    Practising race fuelling reduces gastrointestinal symptoms. Reasonably supported and standard practice.

  • Caffeine improves endurance performance

    Gold· human data

    Among the best-evidenced legal ergogenic aids. Timing matters, and individual tolerance varies — our caffeine calculator shows the time course.

  • Drinking to a fixed schedule beats drinking to thirst

    Not supported

    Aggressive scheduled drinking is how exercise-associated hyponatraemia happens. Thirst is a reasonable guide for most athletes in most conditions.

  • Fat adaptation improves endurance performance

    Unproven

    Low-carbohydrate approaches increase fat oxidation reliably and generally impair high-intensity performance, partly by reducing carbohydrate-use efficiency. Interesting physiology, poor race strategy.

What this means in practice

  • Work out total duration first, then carbohydrate per hour, then convert to actual products and count them into your kit.
  • Rehearse the full plan in at least two long training sessions at race intensity.
  • Drink to thirst unless you have a measured sweat rate and a reason to do otherwise; add sodium for long, hot or salty-sweating efforts.
  • If you use caffeine, time it rather than taking it at the start by habit.
  • Eat afterwards — carbohydrate and protein — particularly with another session inside a day.

When to see a doctor

  • Confusion, severe headache, disorientation or swelling during or after a long event — get urgent medical help.
  • Repeated gastrointestinal distress in races despite practice — worth a sports dietitian's input.
  • Chronic fatigue, illness or menstrual changes across a training block — consider energy availability.

The honest summary

Fuel to duration, drink to thirst, add sodium when you're losing a lot, and practise the whole thing. It's the cheapest performance gain available and the one most often skipped.

Work it out

See also

Frequently asked questions

What should I eat during a long run?
Carbohydrate scaled to duration — nothing needed under an hour, building towards roughly 90 g per hour of mixed glucose and fructose for events beyond about two and a half hours, limited by what your gut tolerates.
Do I need electrolyte drinks?
They earn their place in long, hot or heavy-sweating sessions. As an everyday drink they're unnecessary — our electrolytes page grades the evidence.
Should I train fasted?
Occasional easy fasted sessions are a reasonable tool. Doing it routinely alongside hard training risks under-fuelling, with consequences for bone, hormones and immunity well beyond one session.

Sources

Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.

Last reviewed: