What most runners get wrong
Walk through the first aid station of almost any trail ultra and you will see the same three mistakes playing out in slow motion.
Too few carbs, too late. Most runners underestimate their carbohydrate needs by 30 to 50 percent. They grab half a banana and a cookie at mile 15, then wonder why they are shuffling by mile 25. The body can only store about 90 minutes of glycogen at race effort. After that, it needs a constant external supply, starting from the very first hour.
Drinking only when thirsty. Thirst is a lagging indicator. By the time you feel it, you are already behind. In warm conditions or at altitude, that gap can compound fast. The goal is to drink on a schedule, not on a feeling.
No plan per aid station. "I will eat whatever looks good" is not a fueling strategy. Every aid station has a different food selection, different conditions, and a different leg ahead of it. A vague intention to fuel falls apart the moment you are 18 miles in, your stomach is unhappy, and you cannot remember what you told yourself to eat.
The math, made simple
You do not need a nutrition degree. You need three numbers.
The lower end suits runners new to race nutrition or those with sensitive stomachs. The upper end is achievable with practice and works best when mixing carb types (glucose + fructose together absorb faster than either alone). Start at 60 g and train your gut upward over months of long runs.
The range is wide because conditions vary. A cool overcast mountain race is very different from a sunny desert 50-miler. A sweat rate test during training (weigh yourself before and after a one-hour run, no drinking) gives you a personal baseline. In the absence of that, 500 to 600 ml per hour is a reasonable default for most conditions.
Sodium is the electrolyte most runners lose in meaningful amounts and the one most directly tied to cramping and hyponatremia. Longer races and higher sweat rates push the number toward the top of the range. Electrolyte capsules, tabs, and sports drinks all count. Plain water with no sodium is a risky choice beyond about three hours.
These targets are per hour of moving time, not per hour of elapsed time. If you are hiking a steep climb and your pace has dropped, your carb need drops slightly too. But hydration stays close to target regardless of pace, because you are still sweating.
Building an aid-station fueling plan
A per-aid-station plan assigns a specific intake target to each segment of the course. It takes your hourly targets and translates them into concrete actions at each stop.
Done manually, the process goes like this. Pull up the race's aid station table. Note the distance and estimated time between each stop. Multiply your hourly carb target by the hours in that segment to get the carb total for the leg. Do the same for fluid and sodium. Then figure out which foods and drinks at that aid station add up to those totals. A banana is about 27 g of carbs. A gel is 20 to 25 g. A cup of sports drink is roughly 15 g and 100 mg sodium. A salted potato is 5 g carbs and 50 mg sodium. You work through each station, leg by leg, until you have a written plan.
That process takes most runners two to three hours for a 50-mile course. It also requires assumptions about your pace that may be off by 20 percent on race day, which means the segment times are off, which means the targets are off. Most runners either skip this entirely or do a rough version that falls apart when things get hard.
The runners who execute well on race day are almost always the ones who did the work beforehand: a laminated card in a pocket, or a note on their watch, with the exact intake target for each leg.
How Aerostride builds this plan for you
Aerostride takes your course file, your weight, and your race conditions and does the segment-by-segment math automatically. Every aid station gets its own target: how many grams of carbs to take in, how much fluid, and how much sodium. The calculation accounts for elevation change, which affects both pace and sweat rate, so a steep climbing segment does not get the same targets as a fast descent.
The output is a plan you can actually use: a list of what to eat and drink at each stop, formatted for the aid station menu your race provides. No spreadsheet, no back-of-envelope math, no guessing on the morning of.
It is the difference between a fueling strategy and a fueling intention. One holds up at mile 25 when your brain is not at its best. The other does not.
"Your gut absorbs what you train it to absorb. Practice your race fueling plan on your long runs. The body you train with is the body you race with."
The short checklist before race day
- ✓Calculate your estimated moving time per segment, not total finish time.
- ✓Set a carb target per segment. Write it down.
- ✓Know what the race serves at each aid station. Map your food choices to the target.
- ✓Carry backup calories for the legs where the station is sparse.
- ✓Hydrate on a schedule. Set a reminder on your watch if you need one.
- ✓Practice your full race-day fuel plan at least once during training.
Get your per-aid-station fueling plan, free.
Import your course file. Aerostride builds the plan: carbs, hydration, and electrolytes at every stop, calculated from your course.
Get your fueling plan freeFree to start. No credit card required.