Engine Builder · Block 2
Where the threshold gains actually land.
What it's for
- You finished Block 1, or you already have the aerobic base it builds.
- You want the sharp end — threshold work and VO2max intervals, not more Z2.
- You can give it 5-6 hours a week across four or five sessions.
- You'll swap rowing / cycling / ski-erg / running as your machine.
The arc
Volume expansion with a threshold-dominant middle. Cruise intervals expand toward 3×12 minutes and Norwegian 4×4 returns on top. Declare an equivalent base at intake if you're arriving without Block 1 — the block assumes the base is already in and doesn't rebuild it.
What gets retested
20-minute time trial plus submax HR at a fixed pace, at week 4 and again at week 8-10. Modality-specific TT (2K row / 5K run) at the end if it applies.
Honest outcome ranges
Ranges are honest, not guarantees. Response varies — HERITAGE non-response distributions apply to any structured training program.
What it cites
Seiler 2010 · intensity distribution
The polarised distribution this block's easy/hard split is built on.
Helgerud 2007 · 4×4 intervals
The specific interval protocol behind the VO2max sessions.
Rønnestad 2020 · threshold work
Evidence for the cruise-interval structure that dominates the middle weeks.
Not for you if
- Not a starting point — do Block 1 first, or declare an equivalent base at intake.
- Cardiac or respiratory conditions: clear the intensity work with a clinician.
Sign up on the app, complete the intake, and your first session is on Today within two minutes. Free during beta.