Hi there,

You followed the plan. Every session. Every long run. And somewhere around kilometre 30, it fell apart anyway.

Most people blame their fitness. Or their nutrition. Or their mental strength. The research points somewhere else entirely.

Why stress doesn't care where it comes from

Your body has one stress system. Not one for work and one for training. One. When that system gets activated — whether it's a hard track session or a brutal week of back-to-back meetings — it releases the same hormone: cortisol.

And cortisol doesn't reset overnight just because you slept. It stacks. Which means a hard week at work on top of a heavy training week isn't just tiring. It's actively slowing down your recovery in ways that don't show up on Strava.

A 2022 study found that work stress and training stress run through the exact same biological pathway. When both are high at the same time, your body struggles to recover properly from either — your sleep suffers, your energy drops, and the gap between sessions where your body actually rebuilds gets shorter and shorter.

A heavy month at work and a peak training block at the same time isn't just hard. It's a recipe for going backwards — no matter how disciplined you are. This is why someone can follow a plan to the letter and still fall apart at kilometre 30. The plan only accounted for one type of load. They were carrying two.

What to track instead

1 — HRV on waking, every morning
HRV is your body's honest report on total systemic stress. A suppressed Monday morning HRV tells you last week's recovery is incomplete — before you've touched a single session.

2 — Life load score, not just session RPE
Rate your general load out of 10 each morning. Three consecutive days above 7 is a signal to reduce session intensity regardless of what the plan says. This is what elite coaches call load management.

3 — The two-domain rule
If work is genuinely demanding that week — big deadline, difficult client — downgrade one session. Not cancel it. Downgrade it. Easy instead of threshold. 60 minutes instead of 90. You still get the adaptation stimulus without compounding the cortisol load.

What this means for your fuelling

Under elevated stress, glycogen depletion accelerates. Cortisol actively promotes glycogenolysis — the breakdown of stored glycogen. You burn through your fuel faster, your gut becomes more sensitive, and your ability to absorb carbohydrate at pace decreases.

This is why the wall appears earlier in high-stress periods even when fitness hasn't dropped. The fix: increase your carbohydrate intake on high-stress training days by 15–20%. Start fuelling at 15 minutes rather than 20. Use lower-sweetness products if GI sensitivity is an issue — cortisol increases gut permeability.

The athletes who perform most consistently across a full season are not the ones with the lightest training loads. They're the ones who've learned to account for what they're carrying into each session from the rest of their life — and fuel accordingly.

That's the load management problem. And now you know what to do about it.

Luke & Jamie
Engine Room Nutrition