The UK's toughest winter coastal ultra. 100 miles along Cornwall's South West Coast Path in January — with a 50% drop-out rate and brutal winter conditions.
161km · 4,010m+ · Coverack to Porthtowan. 36-hour cut-off. The UK's hardest winter 100-mile ultra.
4 Running Stones80km · 2,500m+ · Minack Theatre to Porthtowan. 15.5-hour cut-off. Past Land's End along the dramatic southern tip.
3 Running Stones40km · 1,000m+ · Near St Ives to Porthtowan. 8-hour cut-off. Dramatic terrain, dunes and cliffs.
2 Running Stones24km · 500m+ · Godrevy to Porthtowan. Perfect introduction to coastal ultra running.
1 Running StoneThe Arc 100 starts at midday on a Friday in late January and runs through the night — which for most runners means two nights of darkness. The South West Coast Path from Coverack to Porthtowan is relentlessly undulating, with no flat sections. The winter weather can be brutal — storms, high winds, driving rain and cold temperatures are all common.
The course carries approximately 4,500m of elevation despite being a coastal race — the constant cliff path climbing and descending adds up fast. The section after mile 40 around Porthcurno and Land's End is where the race character changes dramatically — granite bouldering, big cove climbs and serious technical running.
The Arc 100 involves at least one full night of running, often two. Include structured night running sessions in your build-up. Practice your lighting setup and navigation in the dark.
Train in wind and rain — don't wait for good weather. The coast path conditions are brutal in January. Your body needs to be conditioned for wet, cold running over many hours.
Every finisher starts slower than training pace for the first 20-25 miles. The back half is where the race is won or lost — the technical sections after mile 40 slow everyone down significantly.
Long gaps between aid stations on the Arc 100 mean extended self-sufficiency. Know your mandatory kit inside out, and carry enough food and water for the remote sections.
The Arc of Attrition runs 100 miles along the South West Coast Path from Minehead in Somerset to Penzance in Cornwall — in January. The coast path is one of Britain's most technically demanding long-distance trails: narrow cliff paths, constant short climbs, mud, roots, stiles and stream crossings that only get worse as the field spreads out and the weather deteriorates.
The opening section covers Exmoor's coastal edge before dropping into North Cornwall. Expect technical cliff paths in daylight transitioning to night running by mid-section for most starters. This is where the adrenaline of the start can get runners into trouble — push too hard in the first 20 miles and you'll pay for it through the Cornish sections. Pacing patience is everything here.
The first major checkpoint at Boscastle provides drop bag access and a brief respite. After here the coast becomes more exposed and relentlessly undulating. This section catches many runners in the middle of the night — managing sleep deprivation, nutrition and cold simultaneously. Having a clear crew and drop bag plan for this checkpoint is critical.
The southern Cornish coast is the most beautiful section and often the hardest. By this point most runners have been moving for 20+ hours. The path underfoot deteriorates with each successive wave of runners compacting the mud. The final miles into Penzance feel endless — but the finish at the Penzance Promenade is one of ultra running's great moments.
Most runners will experience one full night section and many two nights of running if they're in the back half of the field. Night navigation on the coast path requires a reliable head torch with spare batteries, familiarity with the route direction (sea should generally be to your right heading south-west) and the discipline to keep moving even when exhausted.
The Arc is one of Britain's hardest 100-mile races not because of any single defining challenge but because of the unrelenting combination of factors that accumulate over 28-35 hours of racing in January conditions.
The Arc runs in late January — the coldest and wettest period of the British winter. Gales, horizontal rain and temperatures of 3-8°C are entirely normal. Wind chill on exposed cliff tops can feel arctic. Kit failure in these conditions is a genuine safety risk, not just a comfort issue. Test everything in similar conditions before race day.
The total ascent of around 6,000m sounds manageable for 100 miles until you realise it comes in hundreds of short, steep climbs rather than long sustained ones. There are no recovery flats. Every valley requires a descent and re-climb. By mile 60 your quads will know it.
Most runners take 28-35 hours to finish. That means at least one full night of running, often two. Sleep deprivation creates its own challenges: poor decision-making, hallucinations in severe cases, loss of appetite, and the relentless temptation to stop at crew points. Building tolerance to sleep deprivation in training is essential — not optional.
The Arc has one of the highest DNF rates in British ultra running. In bad weather years the drop rate can exceed 60% of starters. This is not a race for your first 100 miles. Runners who finish typically have multiple 50-mile+ finishes and a realistic understanding of what they're taking on. Preparation and experience both matter enormously.
The Arc allows three drop bags at designated checkpoints. Crew access is limited to specific road crossing points and checkpoint locations — study the crew guide thoroughly in advance. Between checkpoints you are self-sufficient; carry everything you need, don't rely on crew appearing at non-designated locations.
The Arc is not a race you prepare for with a standard spring ultra training plan. The race is in January, which means your peak training falls in November and December — the worst weather Britain offers. This is deliberate. You need to build winter-specific fitness and resilience.
Build your longest training block in November with back-to-back long days: 20-25 miles Saturday followed by 15-18 miles Sunday. Do these on technical trail terrain in whatever weather arrives. Treadmill sessions or good-weather only training will not prepare you for the Arc's conditions.
If you've never run through the night before, this needs to change before the Arc. Practice 3-4 hour night runs in your actual race kit including head torch. Understand how your body responds to running at 3am. If you'll crew on sections, your crew also needs night experience.
Every piece of kit you'll race in needs to be tested in January-equivalent conditions. Shoes that drain well. Waterproofs that genuinely perform in sustained rain. Gloves that work when wet. Mid-layers that don't become sodden. Don't discover kit failures on the coast path at midnight in February.
Walking or running sections of the South West Coast Path — particularly the more technical Cornish sections — builds route familiarity and psychological confidence. Even 2-3 days on the path in the autumn will pay dividends when you're navigating in the dark and the rain at mile 70.
Brennan's Coach Note: The Arc requires a different kind of preparation than most ultras. Don't chase mileage at the expense of specificity. Running 70-mile weeks in good weather doesn't prepare you for 35 hours on the coast path in January. Train in conditions. Embrace the darkness. Build your crew into your preparation from the start — their job is almost as hard as yours.
We build bespoke training plans and coaching packages for this race. Get in touch to discuss your preparation.
Get in TouchOfficial Website ›