What is FuelStint?
FuelStint is a fuelling analyser rather than a food diary. It takes each session from Strava and reconstructs the effort second by second, then models two things across it: how far your muscle glycogen fell, and how much you sweated out. The point is the pattern over weeks — where you keep running dry, and how much you'd need to have taken on to avoid it.
The modelling is specific enough to describe. Intensity comes from the Karvonen method using your max and resting heart rate, or from power where you have it, which is why the physiological profile step matters at signup — weight, max and resting HR, optionally body composition. Sweat loss is estimated from your weight, the intensity and the weather along the route. Runs, trail, cycling, swimming and strength all come across from Strava.
Then it turns forward. Feed the simulator a GPX of a course you're targeting and it projects glycogen and hydration over that route, which gives you a carbohydrate and fluid plan for a specific race rather than a rule of thumb. You can try that simulator without creating an account at all.
Two things to know before you sign up. The site is French, with no English version — the modelling is language-agnostic but the interface and docs are not. And it's early: version 0.9.1, free during early access with everything unlocked and no card.
Key Features
Second-by-second effort reconstruction
Rather than scoring a session on its averages, it rebuilds the effort across its duration and models the glycogen curve through it.
Karvonen-based intensity
Intensity is derived from heart rate against your own max and resting values, or from power for cyclists — so the same session scores differently for two riders, as it should.
Sweat and dehydration modelling
Estimates fluid loss from your weight, the intensity, and the actual weather conditions on the route, then tracks it against what you logged drinking.
GPX race simulator
Project glycogen and hydration over a target course to work out carbohydrate and fluid needs in advance. Usable without an account.
Gut tolerance training
Logging intake over time is framed as building carbohydrate tolerance deliberately, rather than just recording what you ate.
It doesn't touch your Strava activities by default
The integration is read-only unless you opt in. There's an "augment my activity" toggle that adds a nutrition summary to your Strava activity description, and it's off unless you turn it on.
Who It's For
- Endurance athletes who keep blowing up late and want to know whether it was fuel, fluid or pacing
- Trail and ultra runners planning what to carry between aid stations
- Triathletes and long-course cyclists who need a fuelling plan tied to a specific course profile
- French-speaking athletes — with the caveat that there is currently no English interface
