Arc of Attrition by UTMB – Arc 25 is a 41.2 km coastal trail race held on January 25 in Cornwall, England — the final day of the Arc of Attrition UTMB World Series weekend. The course runs from St Ives to Porthtowan along the Cornish coastal path, gaining 1,240m (30.1 m/km), with 49.6% of the distance flat or rolling. The course architecture is deliberately deceptive: the first 35km follows fast coastal paths, sand dunes, and headland traverses before all three of the biggest climbs cluster into the final 7km.
The hardest section — 12.2% average, 21.7% maximum gradient — is the final push to the Porthtowan finish at km 41.13. The primary challenge is not gradient but conditions: Cornwall in January means Atlantic storm exposure, ankle-deep mud, and headland wind chill. Registration fees for the 2027 edition are not yet published. The 2026 edition drew 852 finishers with course records of 2:41:25 (men, Kristian Jones) and 3:09:16 (women, Naomi Lang). It suits fast-footed coastal runners comfortable with British winter conditions and the atmosphere of a major UTMB World Series event.