Chapter 03Field Notes
The science behind your riding, one principle at a time.
You don't have one engine. You have six.
Every ride you've ever done trained some of them and ignored the rest. Knowing which is which is the difference between riding a lot and getting faster.
01 · The principle
Different power, different physiology.
Chapter 01 gave you a single number for every ride. Useful, but two rides at 80 TSS can be built from completely different biology. A steady three hours and forty minutes of intervals cost the same and change different things. Your body has several distinct ways of making power, each with its own fuel, its own limit and its own clock. Intensity is what selects between them.
Power as a percentage of your FTP.
FTP, functional threshold power, is the anchor. Zones above follow Coggan and Allen, each a percentage of the athlete's FTP.
02 · The six
Each one has a job, a fuel, and a clock.
These are tools, not grades. Nobody can be elite at all six, but nobody gets fast on only one.
Z1 · Recovery<55% FTP
The rebuild
Riding that lets adaptation happen.
Blood flow without stress. It doesn't build anything directly. It lets what you already did take hold. Skip it and the harder engines never finish their repairs.
So what: if it feels like training, it isn't recovery. The skill here is restraint.
- Trains
- Nothing. That's the point.
- Adapts
- Hours, not weeks
Z2 · Endurance56–75%
The foundation
Long, conversational, mostly fat-burning.
Grows the mitochondria and capillaries every other engine runs on. Slow to build, slow to lose, and the reason pros ride twenty easy hours a week.
So what: this is where most of your hours belong. It's also the engine you recover with between hard efforts.
- Trains
- Aerobic base, fat oxidation
- Adapts
- 3–6 months of volume
Z3 · Tempo76–90%
The workhorse
Hard enough to hurt a little, not enough to stop.
Muscular endurance for long climbs and long days. The most comfortable place to feel like you're training, and the easiest engine to over-use.
So what: the comfort trap. Drift up from Z2 or sag down from Z4 and you land here: fatigue without the adaptation. Use it on purpose or not at all. → Ch 06, Polarization
- Trains
- Sustained power, fatigue resistance
- Adapts
- 4–8 weeks
Z4 · Threshold91–105%
The ceiling
The hardest pace you can hold for about an hour.
This is FTP itself, the line between sustainable and not. Raise it and everything below it gets easier. Every other engine is measured against this one.
So what: FTP has a ceiling above it. Once it sits near 82% of your 5-minute power, more threshold buys nothing until the ceiling moves.
- Trains
- FTP, lactate clearance
- Adapts
- 6–8 weeks
Z5 · VO2max106–120%
The turbo
Three to eight minutes of controlled suffering.
The most oxygen your body can deliver and use. Responds fast and decays fast. The engine that gets you over the top of a climb with the group instead of behind it.
So what: highest return, highest price. Scarce, scheduled, and done on fresh days or not at all.
- Trains
- Oxygen delivery, cardiac output
- Adapts
- 4–6 weeks
Z6–Z7 · Anaerobic/Sprint>120%
The short-hard pair
Thirty seconds to two minutes, then everything.
Attacks, bridges, the final 200 metres. Runs on stored fuel and raw nerve. Quick to train, quick to lose, and only counted as the session when it was the session.
So what: small doses year-round beat big doses ever. Race-deciding, and gone in weeks if you stop.
- Trains
- Lactate tolerance, neuromuscular power
- Adapts
- 3–4 weeks
The question
Can I have all six?
Nobody can. Sprint muscle and endurance muscle are built for opposite jobs, their adaptations blunt each other, and no recovery budget funds six systems at once. Every elite power profile is lopsided.
So don't chase six ceilings. Find the engine blocking your next step and spend your hard days there. FORM answers that question every morning.
You can raise all six. You cannot max all six.
Six adaptation clocks. Six different training problems. One of them is yours right now.
03 · The aha
Your body doesn't know where the stimulus came from.
Five minutes at 115% of FTP is a VO2max dose. Your muscles do not care whether that came from a structured interval in ERG mode in the garage or from chasing a friend up a 14% ramp on Saturday. Same oxygen demand, same cardiac strain, same adaptation signal. The stimulus is the stimulus.
Tuesday · Trainer
5 × 5 min, ERG mode
Basement. Fan. Podcast. Exactly 112% of FTP for exactly five minutes, five times, with three-minute rests.
Saturday · Outdoors
The group ride that got silly
Three long climbs, each one a fight. Nobody planned intervals. The power file says otherwise.
FORM classifies what your body actually experienced, not what the calendar said.
- A ride is named by the engine it loaded, however the loading happened.
- Your "easy" Saturday can quietly be the week's hardest VO2max session.
- FORM will tell you so.
This is why the coach reads the power file and not the workout title. "Endurance ride" is what you intended. What you trained is a fact, and it's the fact that goes in your log.
04 · Two labels that aren't engines
Some rides don't train a system. They spend several.
Six engines cover focused training. Two more labels exist for the rides that weren't.
Mixed
Several engines, one ride
Real doses in three or more hard zones, none of them dominant. Group rides, rolling terrain, a long day with a bit of everything. Mixed isn't a mistake. It's a description: you loaded several systems at once, and the coach counts every one of them.
Race
A situation, not a system
Repeated all-out surges on top of sustained pressure. Racing is the signature, not any one zone. FORM names it Race because pretending it was a threshold workout would hide what it cost.
Every classification comes with its reason in plain numbers.
VO2max
"Eleven minutes above 106%. That's a VO2max session whether you meant it or not. Tomorrow is easy."
Tempo
"Third tempo ride this week. You like this engine. It doesn't need more. Threshold does."
Mixed
"Threshold, VO2 and sprints in one ride. Big day, no target. Plan the next one."
Endurance
"Two sprints for the town sign don't change the story. This was the base ride it was supposed to be."
05 · What it looks like in your log
Eight real rides, one athlete.
Same rider, same summer. Every one of these carries a second word, the Relative Load, which is the next chapter. For now, read the first column: this is what a season looks like when you can see which engine each ride hit.
Notice the VO2max ride: 52 minutes, 51 TSS, smaller than the tempo ride by every Chapter 01 measure, and the more demanding session. TSS tells you the cost. The engine tells you what you bought.
Stop asking how far you rode. Ask which engine you trained.
Chapter 01: what a ride costs. Chapter 02: whether you absorbed it. This chapter: what it actually trained. One more axis and every ride you do will have a name. That's next.
Next chapter: the right dose. Why the same ride is Overload for one rider and Maintain for another.
Field Notes · Chapter 03 · You don't have one engine← 02Next · Chapter 04 · Relative Load →