Km-effort in trail running: the calculation, ITRA points and their limits

The rule: 100 m of ascent equals 1 km

277. That is the km-effort score of the UTMB, the Ultra-Trail du Mont-Blanc: 177 km of racing, and 10,000 m of ascent worth another hundred [1] [2]. The number looks abstract, yet it sums up what trail running is about: the climbing counts as much as the distance.

The rule comes from the International Trail Running Association (ITRA), which uses it to measure how hard races are: 1 km of distance equals 1 km-effort, and 100 m of ascent also equals 1 km-effort [1]. The calculation fits on one line: add the ascent divided by 100 to the distance. A 30 km race with 1,000 m of ascent is therefore worth 40 km-effort; a 15 km introductory race with 500 m of ascent, 20.

ITRA points: a race’s difficulty in a single number

From the km-effort, ITRA grades every race from 0 to 6 points [1]. A race of under 25 km-effort earns no points; from 210 upwards, it is worth 6. These points tell you how much endurance a race demands: they say nothing about its beauty, its technical difficulty or how long it will take you.

Why 100 m? What walkers’ rules of thumb say

Walkers have known the principle for a long time, with different numbers. The French Hiking Federation (FFRandonnée) bases its walking times on 4 km/h on the flat and 300 to 350 m of ascent per hour [3]: an hour of climbing then equals an hour on the flat, which works out at 75 to 88 m of ascent per kilometre. The rule published in 1892 by the Scot William Naismith, still familiar to British hillwalkers, adds an hour for every 2,000 feet of ascent to an hour for every 3 miles of distance [4]: about 126 m per kilometre.

ITRA’s 100 m falls between the two. The figure is not a law of physiology but a handy convention, accurate enough to compare races with one another, and easy to work out in your head. Our guide to walking times covers these walking rules and their variants in detail, and the walking time calculator applies them to your route.

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Two races compared: the shorter one is not the easier one

Take two trail races on the same weekend. The first covers 42 km with 1,000 m of ascent: 52 km-effort. The second is only 30 km, but with 2,500 m of ascent: 55 km-effort. On the race poster, the second looks the gentler option; in effort, it is slightly harder, and its 2,500 m of descent, which the formula ignores, will weigh heavily on your thighs.

That is the whole point of the tool: putting a long, runnable race and a short, steep one on the same scale. But two similar numbers do not make two similar races. The first can be run almost from start to finish; in the second, you will spend a long time walking the climbs, and the clock will show it.

What the rule misses: descents, technical ground, altitude

The formula uses only the ascent [1]. Descents therefore do not count, even though they wear out your legs and slow runners down on steep or technical slopes. Walkers in Germany and Austria do factor them in: the German standard for hiking signposts counts descents at 500 m per hour, alongside its rates for climbing and for the flat [5].

Technical difficulty is not in it either: 40 km-effort on a wide forest track and 40 km-effort across a boulder field have nothing in common. Altitude and the weather, finally, change everything on race day. ITRA knows this: to score runners’ performances, its algorithm takes into account distance, ascent, altitude, race conditions, technical difficulty and finishing time [1].

The ITRA Performance Index, trail running’s other number

Not to be confused with race points: the ITRA Performance Index measures how good runners are, on a scale of up to 1,000 points. It is calculated as a weighted average of a runner’s five best results over the last 36 months; with no results in that period, the index is no longer active [1]. It is mainly of use to organisers, and to runners who want to see where they stand.

Using it to choose your next race

The km-effort comes into its own when you want to step up. Rather than comparing distances, compare km-effort: going from a 20 km-effort race to a 40 km-effort one doubles the commitment, even if the advertised distance changes by only a few kilometres. For a first trail race, our training plan starts from a short race without much climbing.

To progress, I recommend going up one step at a time: from one ITRA points category to the next, rather than jumping straight from 20 to 60 km-effort. Your body copes better with longer efforts when they come in stages, and each race teaches you something for the next: pacing (heart rate zones can help), fuelling, descending.

The detail that changes everything is reading the profile as well as the number. Of two 40 km-effort races, one may hide a long, steady climb, the other a string of short, sharp climbs and punishing descents. The profile, the race rules and the cut-off times fill in what the km-effort sums up.

And once the race is chosen, all that is left is to find the ridge line on the profile, and wonder what the view will be like from up there.

Nolwenn Bastide

Trail running, snow, water, nature and destinations

Nolwenn covers trail running, snow, water, nature and destinations for Outfarer. Curious about everything, from meteor showers to night-train timetables, she has a knack for unearthing the one detail that changes everything, and putting it in a single sentence.

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