I left Roscoff this morning carrying everything I’d spent six months preparing for. The data was as good as it was going to get. The field guide was printed. The trailer was packed. What I hadn’t prepared for — what nobody could have fully prepared for — was a French heat dome sitting directly on top of Day 1.

The morning metrics told the story before I’d moved a single kilometre. Whoop recovery at 42%. Resting heart rate at 50 bpm — the highest number in the entire six-month dataset, eight beats above my personal baseline. The overnight sleep had been six hours of poor quality following the ferry run the day before. The monitoring system I’d built for exactly these moments handed me a Tier 2 prescription before I’d stepped outside.

Tier 2 means one thing: survive the day, not execute it. Heart rate ceiling of 115 bpm. Walk every uphill. Target 30–35km, not 60. Stop by 10:00 regardless of distance covered. The system doesn’t negotiate with ambition. It reads the numbers and gives the tier. My job is to follow it.

What the tier system couldn’t fully account for was what 34°C in full sun on the Breton coast actually feels like when you’re loaded with a trailer. The cognitive fogginess arrived around kilometre 20 — that particular heaviness where thinking becomes effortful and the legs feel disconnected from intention. I found shade twice. Both times the shade was useless. There was no breeze. The air itself felt inert and hostile.

By 17:00 I had covered 34km. Météo-France had just issued an orange heat warning — their second-highest alert level, reserved for conditions that are not merely uncomfortable but genuinely dangerous. I stopped. Not because the plan said to stop at that exact moment, but because the combination of fogginess, the warning, and legs that felt cast in lead made the decision straightforward. The system had already told me this morning what kind of day it was going to be. I just had to trust it.

I ended up in a supermarket — the coldest place I could find — working through a litre of electrolytes and booking a room on my phone. The legs felt like they belonged to someone else. The thought that crossed my mind, sitting on a plastic chair between the yoghurt aisle and the checkout, was whether I could actually do this for seventeen days.

That thought is a product of a body running on heat stress and depleted glycogen. It is not data.

The monitoring system built over six months exists precisely for this: not to tell you the expedition is going well when it isn’t, but to tell you how to get through the days when it isn’t going well. Today was a Tier 2 day. 34km in a heat emergency, correctly managed, is not failure. It is the decision that keeps days 3, 7, and 13 possible.

Tomorrow the alarm goes at 04:00. Moving by 04:30. The cool hours are the only hours that count right now.

983km remaining. The expedition is intact