Energy gels and isotonic drinks during exercise: when and how to combine them

When is fuel during exercise useful?

Extra carbohydrate is often unnecessary for an easy session lasting up to about an hour. As duration and intensity rise, regular carbohydrate intake can help maintain work rate. A practical starting point for 1–2.5 hours is often 30–60 g per hour. Trained athletes in very long events sometimes use more, with multiple carbohydrate types.

These are not compulsory targets. A smaller athlete, a lower intensity or a sensitive gut may require less. Start with the smallest amount that matches the task.

A simple combination formula

1. Choose an hourly target, for example 45 g carbohydrate.
2. Read the labels: if the bottle has 25 g and the gel 20 g, you are already at 45 g.
3. Schedule the gel before your usual energy dip, not after you have already “hit the wall”.
4. Take gels labelled for use with water with several mouthfuls of plain water.

If the drink is your main fluid source, do not mix it stronger than directed. In heat, fluid needs may rise faster than carbohydrate needs, so a separate bottle of water can be useful.

Examples for running and cycling

90-minute run

For a hard session, one gel around 35–45 minutes with water may be enough. If the bottle already contains carbohydrate, check whether the gel is still required.

Three-hour ride

Smaller portions every 20–30 minutes are usually easier to tolerate than a large hourly dose. Combine drink, gel and an easy-to-chew bar while keeping the approximate hourly total consistent.

Marathon

Match the plan to aid stations. Taking a gel just before a station makes it easier to follow with water. Do not depend on an unfamiliar on-course drink that you have never tested.

What to do when the stomach turns

Reduce intensity and pause concentrated carbohydrate for a while; small mouthfuls of water may be easier to tolerate. Afterwards, record how much and how quickly you consumed, the pace and the weather. The problem is often the total dose or too little water, not a single product.

Repeated severe pain, bloody diarrhoea, fainting or persistent vomiting should never be “trained through”; seek medical help.

Race-plan checklist

• Write carbohydrate grams and caffeine, if present, on each pack.
• Plan in 20–30 minute blocks rather than simply “gels per hour”.
• Mark where plain water and the organiser’s sports drink are available.
• Carry one reserve serving without consuming it merely because it is there.
• In heat, separate the fluid plan from the energy plan.

Make sure packs can be opened with wet or cold hands and that wrappers have a secure pocket. These details often determine whether a good paper plan works in a real event.

Related guides

• Gut training: how to train your digestive system for long events
• Isotonic drinks and hydration: an electrolyte guide for marathon runners
• Glycogen loading before a marathon or long ride: a practical 48-hour plan