"Do you think I'm ready?" — the 5 markers I check 🩸

The right question

It isn't how many kilometres you've logged.
It's what's happening inside while you log them.

Volume is visible. Biomarkers aren't — which is why they get ignored.

①  Heart rate variability (HRV)

I don't care about a single day's number. I care about the 7 to 14-day trend. An HRV falling steadily, alongside elevated resting heart rate, is the earliest signal that training load is exceeding your recovery capacity.

What to do: measure on waking, lying down, same time, for two weeks. If it drops three days running, that isn't the week to add the longest long run in the plan.

②  Ferritin and serum iron

The one that surprises me most in runners who feel fine but underperform. Low ferritin — even without clinical anaemia — reduces oxygen transport and affects mitochondrial metabolism. In premenopausal women and anyone training high volume in heat or altitude, loss through sweat, urine and gastrointestinal microbleeding is real and cumulative.

What to do: full panel 8 weeks before the hard block, not the week before the race. Ferritin corrects over weeks, not days. Below 30 ng/mL in a competitive runner already warrants intervention.

③  Hormone profile · PMID:26590935

Rarely discussed in recreational running, central for masters — men and women — training sustained high volume. Low testosterone has a bidirectional relationship with visceral fat: the deficiency worsens the metabolic profile, and excess fat worsens testosterone. That's the loop a masters marathoner doesn't want to activate unknowingly.

What to do: if you're a masters runner with persistent fatigue, muscle mass loss despite training, and poor performance, a basic panel is worth it. Not for everyone — but cheap compared to losing a whole block to undiagnosed overtraining.

④  Body composition — not weight · PMID:38233990

The scale says little. What matters is fat mass versus lean mass. A study comparing cycling HIIT against running HIIT found comparable fat loss between both modalities, with differences in gut microbiota depending on exercise type.

What to do: if you're starting the block carrying excess fat, consider 4-6 weeks of cross-training before raising running volume. It isn't losing specific training time — it's protecting joints while you improve composition.

⑤  Sleep

Technically not a blood marker, but it works on the same logic: a quantifiable signal predicting whether your body absorbs the load. That's where muscle protein synthesis, adaptation consolidation and cortisol regulation happen. Its relationship with HRV isn't coincidence — both are windows into the same autonomic nervous system.

What to do: wearable or sleep diary, two weeks. If you average under 6.5 hours, that's the first problem to fix — before any adjustment to the plan.

Read as a panel, not as traffic lights

None of the five, on its own, tells you "don't run the marathon". What they tell you together is whether your body can absorb the next 12-16 weeks of load without breaking before the start line.

A low HRV with good sleep and normal ferritin is a completely different story from a low HRV with ferritin at 18 ng/mL and 5.5 hours of sleep.

The honesty I owe my athletes

The perfect training plan doesn't compensate for a body that isn't ready to receive it.

Checking these markers doesn't delay your marathon — it protects it.

📖 Full article — 9 min · all five markers with the detail on each panel

Your question today

Of the five, which have you never checked?

Reply with the number. It's almost always the second — and almost always the one that changes the most.

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Coach Henri

USATF · TrainingPeaks · Certified Functional Strength Coach

Have a good weekend. Tomorrow we close with something lighter.