Chapter 06Field Notes
The science behind your riding, one principle at a time.
Mostly easy. Sometimes fierce.
Add up a week of riding and it has a shape: how much was easy, how much was hard, how much sat in between. The fastest endurance athletes on earth converge on the same shape. Most of us never see ours.
01 · The principle
The pros ride easier than you do. And harder.
Stephen Seiler spent years logging what elite endurance athletes actually did, not what they said they did. Rowers, runners, skiers, cyclists. The same pattern kept appearing: around 80% of training time at low intensity, most of the rest very hard, and almost nothing in the middle. Amateurs do the opposite. They live in the middle, where every ride feels like it counts.
A typical amateur week
Everything feels productive.
Every ride a bit hard. Never fresh enough to go truly hard, never easy enough to recover. A lot of fatigue for less return.
A typical elite week
Two speeds, and discipline.
Long and genuinely easy, then short and genuinely hard. More adaptation per hour of fatigue, and a body fresh enough to do the hard days properly.
Seiler and Kjerland, 2006; Seiler, 2010. The pattern held across sports and across decades of training logs. It's the most replicated finding in endurance coaching.
02 · Three buckets
Seven zones collapse into three.
Chapter 03 gave you seven power zones. For the shape of a week, the science uses three, split at the two physiological thresholds.
Easy · S1
Zones 1 and 2
Below the first threshold. Fat and oxygen, conversation pace, hours. Builds the base and costs almost nothing to recover from.
Recovery + Endurance
Middle · S2
Zones 3 and 4
Between the thresholds. Hard enough to hurt, not hard enough to move your ceiling. Real fatigue, less adaptation than either neighbour.
Tempo + Threshold
Hard · S3
Zones 5 and up
Above the second threshold. VO2max and beyond. Minutes, not hours. Raises the ceiling, but only if you arrive fresh enough to do it properly.
VO2max + Anaerobic + Sprint
Seiler's name for the middle bucket when you drift into it by default. It feels like training. It produces fatigue like training. It just doesn't build much. Chapter 03 flagged Tempo as the comfort trap. This is why.
03 · The shapes
A week has a shape. None of them is wrong.
Sort your hours into the three buckets and the week takes one of a few recognisable forms. Each one is the right answer to a different question. The mistake isn't picking the wrong shape. It's riding the same shape all year without knowing it.
Polarized
Big easy, real hard, nothing between. Seiler's elite pattern.
Build · performance
Pyramidal
Mostly easy, some middle, a little hard. The most common shape in real logs.
Base · general fitness
Base
Almost all easy. Building the aerobic engine before asking anything of it.
Winter · early season · back at it
Threshold
Middle-heavy. When deliberately at threshold, or event forced. A flag in base.
FTP development · race specific
HIIT
Hard-heavy. Short, sharp blocks only. Nobody sustains this for long.
Short blocks · time-crunched
Unique
Doesn't fit a pattern. Usually a broken week: travel, illness, one huge ride.
Any phase · read the calendar
04 · One number
How polarized was it? The Polarization Index.
Shapes are a picture. Sometimes you want a number, and a research group in 2019 published one: the Polarization Index. It rewards time at the two ends and penalises time in the middle.
PI = log10( Easy% ÷ Middle% × Hard% )
More easy and more hard push it up. More middle pulls it down.
Treff, Winkert, Sareban, Steinacker and Sperlich, 2019. FORM uses the published percentage form of the index.
05 · How FORM does it
Your week, its shape, and the phase you're in.
Every ride's time in zone is already in FORM. Each Monday-to-Sunday week gets sorted into the three buckets, stamped with its shape and its index, and read against the phase of the season you're in. Open the Polarization card and that reading is the first thing you see.
"Pyramidal in a Recovery week is exactly right. Threshold in a Recovery week, like August 3, is the one to look at. That's a rest week that didn't rest."
- Power zones, never heart rate. The shape is built from what your legs did, not how your heart reacted to heat or coffee.
- Three readings, deliberately unequal. Most weeks simply fit, and say so in one line. A middle-heavy week in Base gets a question: chosen, or drifted into? Only hard riding in a Recovery week gets a flag, and only a flag ever comes with a correction.
- Chosen or drifted. When the middle bucket is heavy, FORM splits it: the planned FTP session you meant to do, and the minutes that leaked from rides meant to be easy. The correction, if there is one, is about the leak.
- Eight weeks in the selector. Pick any week to see its shape, index and reading. A light week below the hours floor is greyed and gets no label; a Unique week says why: one ride carried it, travel, or not enough signal.
Easy days easier. Hard days harder. The middle on purpose, or not at all.
Chapter 03 said Tempo has its place. This chapter said where: chosen, in season, for a reason. The rest of the time, the fastest athletes in the world spend their hours at the two ends, and now you can see whether you do. The shape of a week is only half the answer, though. Which shape belongs to which part of the season is Chapter 07.
Next chapter: Seasons, not sessions. Base, Build, Peak, Recover, and why week three is always the hard one.
Field Notes · Chapter 06 · Mostly easy. Sometimes fierce.← 05Next · Chapter 07 · Seasons, not sessions →