Arc of Attrition by UTMB®
Arc of Attrition by UTMB® – Arc 20K
Perranporth Airfield
Race guide
Updated 18 July 2026
The Arc 20K is the shortest distance in the Arc of Attrition by UTMB, a 22 km route that starts and finishes at Perranporth Airfield and reaches out to Porthtowan before turning for home. With 603 m of climbing and a high point of 187 m, it delivers the flavour of the Arc of Attrition — the rugged coastline of Cornwall — in a distance suitable for runners looking for a punchy day rather than an all-night epic. Though short, the Arc 20K is not flat: the profile drops from the airfield down to near sea level at Porthtowan and climbs back, so the modest total ascent is concentrated into meaningful up-and-down. It is a fast, honest introduction to the terrain and atmosphere of the Arc of Attrition weekend.
The course: an out-and-back to Porthtowan
The Arc 20K begins at Perranporth Airfield at 100 m elevation and runs 22.1 km back to the same finish at the airfield, with a single waypoint at Porthtowan at 9.6 km. That Porthtowan point sits at just 11 m — essentially sea level — which tells you the defining feature of the course: a long descent from the airfield down toward the coast at Porthtowan, then a climb back up over the return leg to the 100 m finish. Because the route falls to 11 m at its midpoint and returns to 100 m at the line, most of the 603 m of climbing is loaded into the second half as you work your way back from Porthtowan to Perranporth Airfield. The high point of the course is 187 m, so the terrain undulates above the coastline rather than climbing any single sustained mountain. Expect rolling ground with the elevation given back and taken again between the airfield and the sea.
Where the race is decided
With only one intermediate waypoint recorded, the shape of the Arc 20K is clear from the elevations: an early net descent to Porthtowan at 9.6 km (11 m) followed by a net climb back to the 100 m finish over the final 12.5 km. That makes the return leg the decisive part of the race. Runners who let the early downhill draw them into a pace they cannot sustain will feel it on the way back, when the accumulated 603 m of ascent has to be paid off against gravity. The smart approach is to treat the first 9.6 km to Porthtowan as controlled and reserve energy for the climbing that dominates the return. Because the high point is 187 m and the profile rolls rather than featuring one long climb, the effort comes in repeated short rises rather than a single ascent — the kind of terrain where consistent, strong-but-steady running beats surging and fading.
How to pace it
At 22 km with 603 m of climbing, the Arc 20K is a distance most trail runners can push, but the course structure rewards restraint on the outbound half. The net drop to Porthtowan at 9.6 km makes it tempting to bank time early; resist that, because the return leg climbs back to the 100 m finish and holds most of the day's ascent. Run the first half within yourself and you will have the legs to keep pushing the rolling ground on the way home. The grounding data lists no intermediate cut-offs for the Arc 20K, so the priority is your own effort management rather than racing a clock between checkpoints. With only the Porthtowan waypoint between start and finish, plan to be self-sufficient for the full loop — carry the fluid and fuel you need to cover roughly 22 km, and keep eating and drinking steadily so the climbing return does not catch you under-fuelled.
Conditions to expect
The Arc of Attrition is a Cornish coastal event, and the Arc 20K's route between Perranporth Airfield and Porthtowan sits close to that exposed coastline, dropping to just 11 m at the sea before climbing back inland to the airfield. Exposed coastal ground can mean wind and changeable weather, so dress for conditions that can shift quickly and be ready for the ground to be wet or muddy underfoot. With the course topping out at only 187 m, altitude is never a factor — the challenge is the repeated up-and-down and whatever the coastal weather brings on the day. Choose shoes with dependable grip for potentially soft or slick footing, and pace the outbound descent to Porthtowan conservatively so you can handle the climbing return to Perranporth Airfield. Run it that way and the Arc 20K makes for a fast, characterful taste of the Arc of Attrition terrain.
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Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-17) · official source
0 km · 100 m · —
9.6 km · 11 m · —
22.1 km · 100 m · —
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