Terrain & Conditions: Trails, Altitude, Heat & Cold

Train the terrain you will race on

Climbing, flat running, descending and walking are different skills, so train each one your race asks for. If your race is much steeper than your training ground, match the climbing per mile and the grades you will face, plan your volume by time and not distance. If you travel to very steep terrain, expect your pace to be about 10 to 15 percent slower than you are used to, and a two-hour run there may cover half the usual distance. That is the terrain, not lost fitness.

Hills and slopes

A 2017 review found that running uphill costs more energy per meter than running on the level, and that the cost rises in a straight line with the grade¹. Hold your effort steady on hills and let pace vary. The guide on grade-adjusted pace covers how effort and pace relate on hills, and the guide on downhill running covers descending. To train a slope indoors, see the uphill treadmill.

Steep climbs, walking and poles

On very steep climbs walking stops costing more than running. In a 2021 study of ten high-caliber male trail and mountain runners, the speed at which they chose to switch between walking and running, and the speed at which running became cheaper than walking, both fell as the incline got steeper, and at 15 degrees (about a 27% grade) the two converged². So hike the steep climbs when running would push you out of your target effort.

Poles help on steep walking. In a 2019 study of 14 mountain running athletes walking uphill on a treadmill at seven angles from 10.1 to 38.9 degrees, poles lowered the energy cost per meter climbed by about 2% to 3% at 25.4, 29.8 and 35.5 degrees and lowered rating of perceived exertion by about 14% to 19% at five of the seven angles³. If poles are in your race plan, they are in your long runs first.

Technical trail

Running technical trail is a skill, so practice it on purpose, including late in long runs when you are tired. On descents, take the most direct line and do not pick your way: you make about a thousand decisions on a one-mile descent, and quick feet are the biggest technical cue.

Wind

In 33 trained distance runners on a treadmill in a wind tunnel, a headwind raised oxygen uptake by 4.7% compared with no wind. Running 1 m behind a mannequin cut oxygen uptake by 2.8% compared with the headwind alone, and did not bring it back to the no-wind level⁴. Sheltering behind another runner helps, but only partly, so run a headwind by effort and let the pace slow.

Altitude

Altitude lowers the pace you can hold, and it starts low. In a 2006 study of eight endurance-trained athletes at simulated altitudes from 300 to 2,800 m, VO2max fell in a straight line, by 6.3% per 1,000 m (range 4.6% to 7.5%), and time to exhaustion at a fixed speed fell by 14.5% per 1,000 m. Both had already dropped between 300 and 800 m⁵.

The signs that normally tell you how hard you are working (breathing, muscle signals and heart rate) stop lining up with your speed at altitude, which makes pacing harder. A 2010 review written for winter-sport athletes recommends time to acclimatize for endurance events: 3 to 5 days if possible at low altitude (500 to 2,000 m), 1 to 2 weeks at moderate altitude (2,000 to 3,000 m), and at least 2 weeks if possible above 3,000 m⁶. In a race at altitude, lower the target for the day and run by effort. The guide on race-day pacing covers it.

Heat

The most important thing you can do in the heat is acclimatize, with repeated exercise in the heat over 1 to 2 weeks, and start training and racing well hydrated (a 2015 expert consensus)⁷. Most of the benefit comes in the first nine to eleven exposures, and it fades quickly, so time it for the last weeks before a hot race. Passive heat counts: the guides on passive heat training and heat suit training cover the options.

Heat pushes heart rate up out of proportion to the work you are doing, and heart rate keeps drifting upward over a long effort, which shifts the relationship between heart rate and how hard you are working, as a 2015 review describes⁸. A heart rate target set in cool weather therefore means something different on a hot day, so run by effort and slow down when it is hot. The guides on heart rate, pace and effort and hydration and electrolytes cover the rest. Heat is also a safety issue: the safety note at the end of this guide covers what to do.

Cold and bad weather

In a 2014 study of nine female endurance athletes running on a treadmill in a climatic chamber from 20 to -14 degrees C with a wind of 5 meters per second, time to exhaustion, running economy, running speed at lactate threshold and VO2max did not differ between temperatures⁹. Cold on its own did not slow them. Slick footing on ice and snow does slow you, so run by effort there. To get used to bad weather, run in it on purpose, on a loop you stop timing.