How to use the GAP Planner
GAP Planner plans a route on a map, or imports one from a GPX, TCX or FIT file or from Intervals.icu. It then predicts your pace and time for every split, taking the climbs and descents into account.
How to use it
- Build or import a route. Draw on the map with road, trail or free-draw routing, or import a file. Elevation is added automatically.
- Read the splits. Use equal-distance splits, or equal-elevation-gain splits for hilly courses where distance splits differ a lot in difficulty. Each split shows gain, loss, suggested pace, estimated time and cumulative time.
- Personalise the pace model with your own Intervals.icu runs, and optionally a fatigue curve for long events.
- Add waypoints for aid stations or crew points, with optional stop time. Then export the route as GPX (and open Garmin Connect courses), or the splits as CSV, Markdown or text.
You can also compare up to four routes side by side. You can also analyse a recorded GPX activity: it shows your actual pace against the predicted pace for every split.
How it works: the standard model
Without your data, the planner uses the energy cost of running on slopes measured by Minetti et al. (2002). They had ten runners on a treadmill at gradients from −45% to +45% and fitted a formula for the energy cost of running at gradient i (rise over run):
C(i) = 155.4i⁵ − 30.4i⁴ − 43.3i³ + 46.3i² + 19.5i + 3.6 (J per kg per m)On the flat, C = 3.6 J/kg/m. The planner divides the cost at each gradient by the flat cost to get a pace multiplier. For the same effort, a split costing 1.66 times the energy takes about 1.66 times as long:
| Gradient | −10% | −5% | 0% | +5% | +10% | +15% | +20% |
|---|---|---|---|---|---|---|---|
| Relative cost | 0.60 | 0.76 | 1.00 | 1.30 | 1.66 | 2.06 | 2.50 |
Note that running costs least at a gentle downhill (about −10% to −20%) and costs more again on steeper descents. Uphill, the cost rises steeply.
How it works: your personal model
Lab formulas describe the average runner, but they can't know your technique or how much you hold back on descents. When you connect Intervals.icu, the planner reads the GPS, elevation and heart rate data from the runs you pick. It works out how your own pace changes with gradient, in 1% steps from −20% to +20%, separately for each heart rate zone. Where your runs have no data for a gradient, it fills the gap from neighbouring gradients or from the Minetti curve. You can smooth the curve, scale its sensitivity to gradient, shift each zone's flat pace, or drag it by hand.
The fatigue curve is built from your past runs of a similar length. It shows how much you slow down over the course of a long run (1.0 = no slowdown, 1.15 = 15% slower), so late splits in an ultra are predicted more realistically than at a constant effort.
Related
References
- Minetti AE, Moia C, Roi GS, Susta D, Ferretti G. Energy cost of walking and running at extreme uphill and downhill slopes. J Appl Physiol. 2002. PubMed
RunTK's tools are for planning and education. They aren't medical advice, and the right numbers for you depend on your health, experience and goals.
© 2026 RunTK.com · All rights reserved