GPX Race Pacer

Grade-adjusted pace (GAP) converts a pace run on a slope to the equivalent effort on flat ground. Running 6'00"/km up a 5% hill takes roughly the same effort as running 4'37"/km on flat terrain.

This tool uses GAP in reverse: given a flat-equivalent target effort, it calculates the actual pace you should run on each gradient.

Elevation affects running pace through metabolic cost. Running uphill requires more energy per meter than running on flat ground. A 5% gradient increases energy cost by about 30%. A 10% gradient increases it by about 66%.

Downhill running reduces cost, but less than you might expect. A -10% downhill only saves about 40%. The minimum energy cost occurs around -18% gradient. Beyond that, steeper downhills actually cost more because of eccentric braking forces. This is why you cannot make up all your lost time on the downhill side of a hill.

GPX elevation accuracy varies by source. Files from devices with barometric altimeters (most Garmin, Coros, and Apple Watch models) are accurate to within 1-3 meters. Files from phone GPS may be off by 10-30 meters at individual points.

This tool smooths the elevation data to reduce noise, but the quality of the input GPX still matters. For best results, use a GPX file from a watch that recorded the actual course, or download the official course GPX from the race organizer.

Even effort is almost always faster than even pace on a hilly course. Running even pace means you are working too hard on the uphills and coasting on the downhills. The energy you waste pushing uphill is not recovered on the descent.

Even effort pacing, which this tool calculates, means slowing down on uphills and speeding up on downhills while maintaining the same metabolic output throughout.

You can use this tool for trail races, but with caveats. The cost model assumes a firm, even surface. Trail running adds variables it does not account for: technical terrain, soft ground, and altitude effects above 1000m.

Use the pace recommendations as a reference for effort distribution, not as exact targets. The relative pacing between segments is still valuable even if the absolute pace numbers need adjustment for trail conditions.

This tool uses the Minetti et al. (2002) metabolic cost model, published in the Journal of Applied Physiology. It describes the energy cost of running as a function of gradient, based on treadmill measurements from -45% to +45%.

The key insight: a 10% uphill increases cost by 66%, but a 10% downhill only reduces it by 40%.