Arc of Attrition by UTMB®, live.

A hundred miles of cliff path in January

Four races on the South West Coast Path in the middle of the Cornish winter, all of them ending at Perranporth Airfield.

Arc of Attrition by UTMB runs from Friday 22 to Sunday 24 January 2027. The organiser publishes four races: the Arc 100M at 173 km and 5,507 m of ascent from Coverack, the Arc 100K at 82.7 km and 2,708 m from Land’s End, the Arc 50K at 49.4 km and 1,458 m from Harlyn Bay, and the Arc 20K, a 22.1 km loop with 744 m from Perranporth Airfield. Every race finishes at the airfield. The event began in 2015 as a single 100-mile race with 50 runners.

The course is the coast path itself, a National Trail of undulating cliff paths and cliff edges that the organiser calls difficult, steep and arduous in places, run in the heart of winter. The long races pass Kynance Cove, Cape Cornwall, Botallack, Zennor Head, Hayle, Mexico Towans, the Dunes of Doom and Godrevy Head. In January most of the 100-mile race and the end of the 100K are run in the dark.

For the people waiting at an airfield on a Cornish winter night, Livebib makes the gaps between aid stations visible. The runner shares a link to their own broadcast. It opens in a browser with no account and no app, and shows the position on the course line, distance covered and a finish estimate that updates as the race goes. In coves and under headlands the phone can lose signal. The position is then carried forward along the course and marked as estimated, never shown as measured.