Grade-Adjusted Pace (GAP) — Comparing Effort Across Hills

By Runsense · Reviewed by Raphael Crawford-Marks, Founder · Last reviewed June 10, 2026

Grade-adjusted pace (GAP) estimates what your pace on a hill would equate to on flat ground — so you can compare a hilly run to a flat one and judge your true effort, instead of chasing a pace number the terrain has made meaningless. This is general training guidance.

The problem it solves

Running uphill at a given effort is much slower than the same effort on the flat, and downhill is faster — so a fixed pace target is simply wrong on hills (it cooks you on the climbs and undersells you on the descents). GAP translates your actual pace on a slope into the flat-ground pace that would have cost the same effort, making efforts comparable across different terrain.

The physiology behind it

GAP rests on a well-measured relationship: the energy cost of running rises steeply as the grade goes up, and *falls* as the grade goes down — but only to a point. For running, the cost bottoms out around a −20% downhill grade (a moderate descent); on steeper descents it climbs again, because you spend energy braking1. GAP algorithms use this energy-cost curve to convert slope pace into equivalent flat pace.

How to use it well

GAP (shown by Strava and many watches) is most useful *after* a run — for comparing a hilly effort to a flat one, and for seeing your real effort on climbs in your training log. But the better habit *during* a hilly run is simpler than any number: pace by effort, heart rate, or the talk test, and let the watch compute GAP afterward. Don't try to hold a flat-ground pace target up a climb — that's exactly the mistake GAP exists to expose.

Its limits

GAP is an estimate. Different platforms use different algorithms, and none can fully capture trail-specific factors like technical footing, mud, or the cost of careful descending. Treat it as a useful approximation for comparing efforts — and on real climbs and descents, let effort be the master and the number be the footnote (see terrain & conditions).

Sources

  1. Minetti AE, Moia C, Roi GS, Susta D, Ferretti G. Energy cost of walking and running at extreme uphill and downhill slopes. Journal of Applied Physiology 93(3):1039-1046 (2002). (Treadmill study of the metabolic cost of running/walking across slopes) ↩

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