Trail Running Pacing — Climbs, Descents, and the GAP Trap

On the road, holding 4:30/km is a mechanical task — you watch your wristwatch. On a trail, holding 4:30/km on every kilometer would have you running uphill kilometers at VO₂max and downhill kilometers in jog mode. The answer is to pace by effort: target a steady perceived exertion, accept whatever pace the terrain returns.

Heart rate is the closest objective proxy. Most trail racers hold zone 2 to low zone 3 for races over four hours; zone 3 to threshold for two- to four-hour events.

Strava's GAP and the Minetti model both convert pace on a slope into the flat-ground pace that would have cost the same energy. A 6:30/km on a 5 % climb is roughly equivalent to a 5:00/km on flat ground. GAP lets you compare a steep mid-race climb against an opening flat kilometer — useful both for training analysis and for race-day pacing checks.

Caveat: GAP captures energy cost, not the marginal cost of fatigue, terrain technicality, or breathing rate. Use it as a guide, not as ground truth.

The aerobic cost of running versus walking crosses around a 15 % grade for most fit runners. Above ~15 %, hiking with hands on quads is cheaper per meter of vertical gain. Walking the steep parts costs you almost no time and saves significant muscle damage — which lets you run faster on the descents and the flat sections that follow.

Practical rule: if you can't maintain your breathing-rhythm running, switch to power-hiking. Don't white-knuckle through a 12 % climb just to say you ran it.

ISSN 2018 maxes out at 60–90 g of carbohydrate per hour. That holds for trail too, but on long efforts (5+ hours), you also need protein and salt. Most ultra runners do well with 200–300 calories per hour, of which 50–70 % is carbohydrate, plus 500–1000 mg of sodium per hour in hot conditions.

Practical rule: aid stations are not just water stops — they're mandatory eating stops. Skipping fuel for two stations is how blow-ups happen.

Trail kilometers vary by a factor of 3 in effort. A flat valley kilometer takes 5 minutes; a technical climb kilometer at the same effort takes 15. Pacing by kilometer drives runners insane. Pace by aid-station segment instead — "hold steady effort to the next aid" — and check progress against your time budget at each one.

Trail courses reward homework. Study the elevation profile, identify the three or four sections that will define your day, and pre-plan effort + fueling for each. Our pacing engine handles the math; you handle the discipline.

See our race pages for course-specific pacing on iconic trail events.