How to plan fuel and hydration for an ultra

The planner turns your hourly rates and carry capacity into a leg-by-leg plan: how many carbs, how much water and salt, what to carry, and what to pick up at each station.

Why plan fuel and water

A race can go wrong on one leg even when the overall numbers look fine. The limit is usually local: the next water point is too far for the flasks, a climb takes longer than expected, or a station has no water to mix a drink. A useful plan works leg by leg, against what you can carry and what the next station provides.

The hourly rates are yours, not a universal formula. Sweat rate, carb tolerance and salt loss vary, and the plan turns your numbers into quantities you can pack and carry. Test them in training; the plan cannot tell you how your stomach will behave on the day.

What the plan needs from you

The fueling plan uses the values in your profile. They are the part the route cannot tell the planner: how much you eat and drink, and how much you can carry. Change one and the quantities change.

• Carbs per hour, water per hour, and salt per litre of water.
• How much fluid you can carry at once.
• Carbs per snack and carbs per drink mix serving.
• Aid-station time and drop-bag time.

How the plan is built

A leg is the section between two consecutive aid stations. The leg is the unit because that is where the constraints apply: you leave a station with a limited pack, and the next station is the next chance to resupply.

• For each leg, the planner multiplies the leg's duration by your rates to get the carbs, fluid and salt you need.
• Water is rationed across the run between two water points. If you cannot carry the whole stretch, the plan tells you what to drink from your flasks and what to pick up at the next water point. The comparison is against what the flasks can hold at once, not the total for the race.
• Salt is not rationed; the plan keeps the full amount. Salt capsules are packed at the start and refilled from drop bags.
• The total number of snacks is set first, then shared out to the legs that need them most, with extra going to legs that have room. You cannot carry an unlimited number, so the plan allocates the food instead of giving every leg the same amount.
• Drink mixes are only prepared at a station with water. A leg that leaves a dry station gets no new mix prepared; it uses what is already in the pack and the snacks already in the plan.
• The plan treats a station with a drop bag as a resupply point. That keeps the arrival time tied to the aid station instead of counting the same stop twice. The packing list shows what to carry out of each station.

An example

These are the last five legs of the Swiss Alps 100 km example, from Chäserstatt to the finish. The full plan has 12 stations; the table keeps six of them. The rates are the default example profile: 60 g of carbs and 500 ml of water per hour, 500 mg of salt per litre, and 1 L of carry capacity.

Fluid need is the physiological need for the leg. Mix and plain are 500 ml flasks; together they are what you carry, and this example carries 1 L (two flasks). The first two legs need more than that, and the plan flags the shortfall. The planner also shows carbs from station food, drink-mix servings, plain water, snack counts and salt capsules.

The table is meant to be read leg by leg. The largest need is not automatically the problem; the problem is a leg whose need is larger than what can be carried out of its station. That is why the plan shows the fluid need and the flasks next to each other.

What it does not do

It is a planning aid, not medical or nutrition advice. Test the plan in training. Heat, effort, stomach problems and personal tolerance can change what you need. Aid-station services in the race data may be incomplete, so check the organiser's information before race day.

Cite this page: “How to plan fuel and hydration for an ultra”, UltraTrailPlan, https://ultratrailplan.com/guides/trail-running-fueling-plan/.