Arc of Attrition by UTMB®
Arc of Attrition by UTMB® – Arc 50K
Harlyn Bay → Perranporth Airfield
Race guide
Updated 18 July 2026
The Arc 50K is the short-course entry into the Arc of Attrition by UTMB, running 49 km down the north Cornish coast from Harlyn Bay to Perranporth Airfield. With just 864 m of ascent and a high point of only 100 m, it reads on paper like a fast, forgiving day out. That number is deceptive. This is coast-path running, where the elevation profile hides a stream of short, steep climbs in and out of every cove, and where the surface — sand, rock, mud and cliff-top singletrack — sets the real pace. Starting at sea level (6 m) at Harlyn Bay and finishing on the airfield above Perranporth at 100 m, the route strings together some of the most exposed and beautiful running on the South West Coast Path. It is a race where honest, patient effort beats early ambition, and where the runners who respect the terrain and the weather are the ones still moving well at the finish.
The Course and Terrain
From the start at Harlyn Bay the route heads down the coast through Mawgan Porth (17.8 km, 6 m), Porth (24.8 km, 5 m) and Holywell Bay (37.5 km, 6 m) before climbing the final stretch to Perranporth Airfield at 49.4 km and 100 m. Every named waypoint sits within a few metres of sea level, which tells you the story of the profile: this is not a course with a single big climb to conquer, but one that repeatedly drops to the beach and hauls back up onto the cliffs. Underfoot, expect constant variety. Firm coast-path singletrack gives way to soft beach sand, boggy field edges, rocky steps and slick descents. The 864 m of total ascent arrives in dozens of short, sharp bites rather than sustained grinds, so rhythm is broken again and again. Treat the terrain, not the elevation figure, as the difficulty — strong hikers who can power up the little pitches and run the flats and downhills confidently will make the best time here.
Where the Race Is Decided
With no dominant climb, the Arc 50K is won and lost in the cumulative cost of the coves. The stretch between Mawgan Porth (17.8 km) and Porth (24.8 km) covers roughly 7 km of the most broken coastline, and the section from Holywell Bay (37.5 km) to the finish carries the only sustained net gain on the course — the climb from sea level up to the airfield at 100 m in the closing kilometres, exactly when legs are least willing. The smart move is to run the first half within yourself. The waypoints at Mawgan Porth, Porth and Holywell Bay are natural checkpoints to assess how you feel: arriving there fresh rather than frazzled is the goal. Save something for the last 12 km after Holywell Bay, because that final rise to Perranporth is where tired runners bleed time and where a disciplined pacer moves through the field.
How to Pace and Fuel It
The listed waypoints — Harlyn Bay (0 km), Mawgan Porth (17.8 km), Porth (24.8 km), Holywell Bay (37.5 km) and the finish (49.4 km) — give you natural segments to plan around. Break the race into these four chunks and set a conservative time target for the first two: banking fatigue early on a coast path always costs more than it saves. The gaps between waypoints run up to around 18 km at the start, so carry enough fluid and calories to be self-sufficient between them rather than relying on frequent top-ups. Aim to eat little and often on the runnable flat sections along the beaches and cliff tops, where digestion is easiest, and use the short climbs as walking-and-eating breaks. Because the course never goes high, altitude is a non-issue, but the constant surface changes and the soft sand sap energy quietly — factor in a slower average pace than a road or smooth-trail 50 km, and keep fuelling steady all the way to that final pull up to the airfield.
Conditions to Expect
This is exposed north-Cornwall coastline, and the weather is a full participant in the race. Atlantic wind hits the cliff tops without shelter, and rain turns the coast-path mud and rock steps slick and slow. Even on a fair day the sections along open beach can mean headwind, soft footing and spray. Dress and pack for changeable conditions: a wind- and waterproof layer earns its place even when the forecast looks kind. Grip matters more than cushioning here — shoes with confident lugs will save you on the wet descents into the coves and the muddy field edges between them. Watch your footing on the rocky, root-laced cliff-path sections, where a careless step is the most likely way to end a good day. Run within the surface, respect the wind on the exposed tops, and the Arc 50K rewards you with a genuinely spectacular, honest coastal ultra.
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Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-17) · official source
0 km · 6 m · —
17.8 km · 6 m · —
24.8 km · 5 m · —
37.5 km · 6 m · —
49.4 km · 100 m · —
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