How many
gels, really?

01 / The short answer

How many gels
you actually need

Your muscles store a few hundred grams of carbohydrate as glycogen, your liver around another hundred. At marathon effort you burn through it fast. For most runners the tank runs low after roughly 90 minutes to 2 hours, which is why the wall tends to arrive somewhere between 30 and 35 kilometers.

Gels do not refill the tank. They slow the drain. Every gram you take in is a gram your muscles and brain do not have to pull from stores, so the stores last to the finish.

The plan, by distance

• 10K: one gel about 15 minutes before the start, during the warm-up. Nothing during the race, stored glycogen covers it.
• Half marathon: a gel before the start, then from 30 minutes in about 40 to 60 grams per hour. Under about 75 minutes, the gel before the start is enough.
• Marathon: a gel before the start, then from 30 minutes in about 60 grams per hour, one 30 gram gel every 30 minutes. Up to 90 grams per hour with a trained gut and products that blend glucose and fructose.
• Caffeine, optional: making every third gel a caffeine gel gives a lift in the second half, if you have tried it in training.

02 / Make it work

Train your gut
like a muscle

The number from the calculator only works if your stomach has done it before. Research on gut training shows that a few weeks of practicing race-day intake during training cuts stomach problems and improves how much carbohydrate you absorb.

Use every long run over 90 minutes as a rehearsal. Same gel, same timing, same amount of water. If you have never fueled before, start at 30 grams an hour and add about 10 grams an hour every week or two until you reach your race target.

Three mistakes that cost the last 10K

• Waiting until you feel empty. By then it is too late to catch up. Start before the gun with a gel in the warm-up, take the next 30 minutes in and keep a steady rhythm.
• Trying something new on race day. A new brand, a caffeine gel you have never had, the sample from the expo. Race with what you trained with.
• Gels without water. A gel is concentrated. Take it with a few sips of water at an aid station so it empties from the stomach and does not sit there.

Carb loading,
the short version

For a 10K you do not need to load, a carb-rich dinner the day before is enough. Before a half marathon, eat extra carbohydrate the day before, around 8 grams per kilogram of body weight. Before a marathon, 10 to 12 grams per kilogram per day for the 1 to 2 days before. Rice, bread, pasta, potatoes, juice, or a sports drink on top of meals. Go lighter on fiber and fat so the volume fits.

Expect to weigh 1 to 2 kilograms more on race morning. That is water stored together with glycogen, a sign the loading worked. On race morning, a carb-rich breakfast 1 to 4 hours before the start, with about 500 ml of fluid, tops up the liver after the night. Then the gel in the warm-up, and you are ready for the gun.

Fueling is one part of the race. The other is arriving with the fitness to hold your pace. The Long Run guide covers the session where both get built.