Monotony: the number that quietly kills your training blocks

And your watch doesn't even try to show it.

Last Friday my own system flagged me red. Readiness 48 out of 100. HRV down to 35 ms — the lowest in two weeks. Resting heart rate up, Body Battery on the floor.

I looked through my training log for the culprit. It wasn't there.

I hadn't overtrained. For three nights straight I sat up late over code — work, a deadline, too little sleep. Zero hard sessions. And yet my body reacted like after a hard block: lowered HRV, elevated resting rate, a „slow down” signal.

Because my autonomic nervous system didn't care whether the fatigue came from hill reps or from a laptop. Stress is stress. And for three days I served it to myself in the same dose, no break, no variation.

This is monotony. And it's one of the most underrated reasons good training plans fall apart.

What training monotony is

The concept was introduced by Carl Foster in the late 1990s. The definition is simple, the consequences less so: monotony is the lack of variation in stimulus over time.

It's not about how much you train. It's about how similar your days are to one another.

Foster showed you can quantify „strain” — the real load on the body — by multiplying weekly load by monotony:

And here it gets interesting. Two runners can cover the same weekly mileage, with the same total load — yet one of them ends up far more wrecked. The difference? Distribution.

A week with one hard accent, a zero day and a long run = low monotony, the body gets time to adapt. Seven days of „easy 10 km” = high monotony. Looks healthy. It's a trap.

That second week has neither a truly hard day (to give a stimulus) nor a truly easy one (to give recovery). Everything is medium. The body never gets the „rest now” signal — so it accumulates fatigue quietly, until it breaks.

In Foster's research it was exactly the spikes in monotony and strain — not volume itself — that best predicted illness, overtraining and injury.

Why your watch doesn't see it

Open Garmin, Coros, Suunto — whatever you wear. You'll see individual sessions. Distance, heart rate, power, maybe some „training load” per session.

What you won't see? The pattern.

The watch looks at today's run in isolation. It doesn't tell you: „this is your sixth similar day in a row, you're missing contrast, you're entering the zone where fatigue starts to accumulate.” Because that takes not measuring one session, but reading the rhythm of the whole week.

That's the difference between data and interpretation. The watch gives you numbers. It doesn't tell you what they mean once you line them up over time.

For an ultra runner this is especially treacherous, because our training is monotonous by nature — lots of easy volume hours in the same zone. It's easy to fall into a rhythm where every day looks the same, the miles add up, everything is „green” on the watch — and strain creeps up quietly.

My case: monotony is my recurring problem

I'm not writing this as someone who's cracked it. I'm writing as someone who gets caught by it regularly.

Monotony is my personal Achilles' heel. I tend to fall into a rhythm where day after day I run variations of the same thing — and I need to be watched so I introduce contrast. Hard days should be hard, easy ones truly easy. Without that my strain climbs, even if the mileage looks reasonable.

And the Friday coding story added a second layer few people talk about: life load falls into the same bucket as training load.

Working nights, sleep deprivation, stress, a kid, a deadline — your nervous system doesn't keep separate books for „sport” and „the rest of life.” It all sums into one pool of fatigue. You can have a perfectly distributed training plan and still hit the wall, because life added stress monotony that no watch recorded — because it wasn't in any activity.

That's why three nights at the laptop gave me a reading like after a hard block. And that's why the red alert was right — even though I „did nothing”.

What I do about it (and what you can do)

I built myself a system that reads training monotony as a signal in the daily report — the variety of sessions across the week, computed from the load distribution (a Foster-style index), alongside HRV, resting heart rate and load. When variety of stimulus drops, I get it served up before strain does me harm. A system that says „rebuild the week,” instead of waiting for an injury to do it for me.

One honest clarification: the system doesn't measure work stress directly — a sleepless night at the laptop isn't an activity, no watch records it. But its effect shows up the next morning in HRV and resting heart rate — and that's exactly what gave me Friday's red alert. Two different signals — training monotony from the load, life stress through the ANS — but one pool of fatigue.

But you don't need my system to start. You need three habits:

The simplest test you can run without any app: look at the last seven days and ask — how many of them looked the same? If the answer is „most,” no matter how easy they were. You have monotony. Add contrast before your body adds it for you.

Tomasz · UESCA Certified Ultra Coach · Founder, UltraFlow™
Firefighter, Polish State Fire Service. Mountain ultra runner. SOG 160 km, Bieg Ultra Granią Tatr 71k, Mityczny Bies 135k.