Trail · Ultra · Running
A constant carb target in g/h does not produce evenly spaced intakes in kilometres. Elevation shifts everything, and the plan does that maths.
Computed just now by the engine, on 21,0 km of real GPS track.
The terrain carries the fuelling points directly. Not a chart on one side and a list on the other.
| 0,5 km | 00:06 | Eau (flasque 500 mL) | 100 mL |
| 0,7 km | 00:08 | Maurten Drink Mix 320 (bidon 500 mL) | 100 mL |
| 2,0 km | 00:22 | Maurten Gel 100 | 1 gel |
| 2,6 km | 00:30 | Eau (flasque 500 mL) | 100 mL |
| 3,4 km | 00:42 | Eau (flasque 500 mL) | 100 mL |
| 3,5 km | 00:45 | Maurten Drink Mix 320 (bidon 500 mL) | 100 mL |
This is the production engine running on a fixed course. Change the target time or the carb rate and the plan recomputes.
Method
The GPX is split every 500 m. Each segment gets an effort coefficient derived from Minetti's work on the energy cost of running on a gradient. Your target time is spread in proportion to that cost: that is your race clock.
Carbohydrate and fluid do not follow from one another. At 90 g/h, how much you drink varies twofold depending on the products. The engine tracks both targets and triggers an intake as soon as either one falls behind.
You declare your gels, bars, bottles and refills. The plan sticks to them, tells you when each runs out, and refuses to promise an intake your pack cannot deliver.
The answer depends on how long you will be out there, not on the distance. Here are the usual ranges; the tool starts at 60 g/h and you move the slider wherever you want.
Glycogen stores nearly cover it. Fuelling is mostly there to stop you fading at the end.
The most common range in trail running. Above 60 g/h, mixing glucose and fructose starts to help absorption.
On an ultra the limit stops being the requirement and becomes your stomach. Steady intakes go down better than large ones spread far apart.
What these ranges do not settle is when to take each gel, each sip, each bar. That is what the calculator does from your track. Need your finishing time first? The pace and split calculator is free and needs no account.
On rolling terrain, sixteen minutes apart can mean twice the distance covered. That is exactly what a "gel every 5 km" plan cannot see.
| Window | Duration | Distance | Pace |
|---|---|---|---|
| 04:03 → 04:19 | 16 min | 1,5 km | 10:40 /km |
| 05:43 → 05:59 | 16 min | 3,3 km | 4:51 /km |
Capabilities
Uphill you eat every 1.5 km, downhill every 3.3 km, for the same time interval.
Export a GPX route with one waypoint per intake. The watch warns you as you approach.
8 gels, 2 bars, 3 flask refills: the plan works with what you are carrying.
A drink at 6 g/100 mL tops out at 36 g/h. The plan says so instead of letting you believe otherwise.
A target in mL/h, independent of carbohydrate, with water as a product in its own right.
Pick your gels, bars and drinks by brand from the built-in catalogue, or add your own by hand. The plan works with what you actually eat, and respects the order of preference you set.
Or enter your own: name, carbohydrate, volume. They are saved to your account and offered on every new race.
Feedback
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Between 30 and 60 g/h for under two hours, 60 to 90 g/h on a trail run of 2 to 4 h, and up to 90 to 100 g/h on an ultra if your stomach tolerates it. Above 60 g/h a glucose-fructose blend absorbs better than a single sugar. These ranges are a starting point: the tool's slider begins at 60 g/h, and the real question, the one the plan answers, is at what minute and what kilometre to place each intake.
The usual guide is 400 to 800 mL per hour, adjusted for heat and how much you sweat. Volume does not follow from carbohydrate: at 90 g/h, whether you run on gels and water or on a concentrated drink changes how much you drink twofold. That is why the tool treats hydration as a separate target in mL/h and triggers a sip as soon as the curve falls behind.
Distance matters less than time on your feet: it is your hours of effort that set the total to take in. On a hilly 30 km in 4 h at 75 g/h you need around 300 g of carbohydrate, roughly ten gels or the equivalent in drink and bars. The tool does that calculation from your GPX and your target time, then checks that what you are actually carrying covers it.
From the energy-cost polynomials of Minetti et al. (2002), which measure the cost of running and walking by gradient. Three corrections are applied to match the reality of trail running: the saving from running downhill is only partly converted into speed, braking costs you beyond −10 %, and the model switches to power hiking on steep gradients. The constants are documented and adjustable.
The distance. The waypoint is placed at the kilometre computed for that intake. As long as you hold your target time the two coincide; if you drift, the alerts follow the course, which is the right behaviour for fuelling.
Any watch that can import a GPX route with waypoints. The import instructions provided target the Suunto app. Waypoint syncing is reported as more reliable on Android: worth checking on your own setup before race day.
Not yet. The current engine models running; on a bike, speed depends on power, aerodynamics and rolling resistance, which needs a different model. We would rather say so than sell you an approximate calculation. Leave your address on the relevant page to be notified.
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