Written by James Frost, founder of Flaming Phoenix and maker of Phoenix Bars. Updated August 2026.

Multi-day training camps have quietly become one of the best things in UK fitness. Several sessions a day, big terrain, proper recovery, and a group of people pushing each other. They also create a nutrition problem most attendees only discover on day two: you are burning far more than a normal training day, several days in a row, often with your appetite blunted by effort, early starts and cold water.

Throughout this guide I'm going to use one camp as the worked example: Camp Kaizen, who run hybrid training camps in the Lake District, in the foothills of Scafell. I know the founder, George, and his camps are the clearest picture I can give you of what a properly structured multi-day training load looks like, and therefore what it costs to fuel. The numbers and principles apply to any camp of this shape.

What a Camp Kaizen weekend actually looks like

A Kaizen camp packs eight or more sessions into a weekend. Team trail runs of 5 to 15km. Strength and conditioning sessions. Group hikes of two to five hours with real Lakeland ascent. A cold plunge every day. Campers sleep in glamping accommodation on site, all meals are included, locally sourced and plentiful, and the camps are grouped by fitness level, so the same structure works whether you're an experienced hybrid athlete or earlier in your journey. They've been covered in Men's Fitness and Sustain Health, and they run their own mountain hybrid race in the Lakes each September for anyone who wants to test the training under race conditions.

That structure is brilliant for training effect. It's also exactly the kind of schedule that quietly outruns most people's eating.

What a camp day really costs

Take the Kaizen day above: a morning trail run, a strength session, then an afternoon fell hike. A 10km trail run burns roughly 600 to 900 calories depending on your weight and the terrain. A three to five hour hike with real ascent adds 1,200 to 2,000 more, which you can check against your own numbers with our hiking calorie calculator. A gym session adds another 200 to 350. Stack that on top of what your body burns just existing and a full camp day can clear 4,000 to 5,000 calories. Most people eat nowhere near that, and the shortfall compounds: under-fuel Friday and Saturday's legs feel it, under-fuel Saturday and Sunday's summit feels like survival.

Why appetite lets you down exactly when you need it

Hard efforts suppress appetite. So do cold plunges, early starts and the general adrenaline of camp, and a Kaizen weekend includes all three daily. The result is that the days you most need to eat big are the days you least feel like eating. The answer is not forcing down enormous plates. It is calorie density: getting more energy into smaller, easier portions, and eating little and often between sessions rather than relying on three sit-down meals to carry the whole load. Our guide to high calorie snacks ranks the options by calories per gram.