Choosing a bike zone system (Yousuli vs Coggan)

The two systems

The Hub ships two named bike power zone systems:

• Yousuli 8-band (default). Splits the sweet-spot region into two sub-bands (3a and 3b) for more precise prescription. Upper bands (5, 6, 7) require W' from a CP test for accurate placement; without W' they render "Need W' data".
• Coggan 7-zone. The classic Andy Coggan model that most cycling literature describes. All seven zones are anchor-relative and always render with watt ranges; W' is not required.

Both systems share the same bike power anchor: Critical Power if a CP test has been logged, otherwise FTP. See Zone anchor methodology.

What it changes

Switching systems changes only the named band display. Specifically:

• The dashboard zone table renders with the new band names and ranges.
• The activity-detail time-in-zone bars render with the new band names.
• The sport PDF report renders with the new band labels.

What it does NOT change

• Threshold metrics: CP, FTP, W', CSS, run threshold pace, run CP. Unchanged.
• AT / ANT / VO2max detection. Unchanged.
• Load, IF, AdjP, Fitness, Fatigue, Form. Unchanged.
• Power curve, best efforts, MMP. Unchanged.
• Activity time-in-zone storage. The underlying power_zone_seconds JSON on each activity continues to be keyed against the Yousuli 8-band definitions; the display layer maps to the active system at render time.
• Run pace, swim pace, HR zones. Phase B is bike-only.

Who can change it

The choice lives on the athlete record (zone_system_bike). Permissions:

• Coaches can change it for any athlete on their roster (free or premium) via the athlete edit page at /coach/athlete/<public_id>/edit/.
• Premium athletes can change it themselves at /settings/zones/ (linked from the main settings page).
• Free athletes see a polite "ask your coach" page at the same URL; they cannot self-edit, but their coach can change it for them at any time.
• Free athletes without a coach are stuck on the default unless an admin sets it.

The choice is per athlete, not per coach or per team. Coaches with mixed-preference rosters can set each athlete's system independently.

When to pick Coggan

• Athletes coming from a TrainingPeaks / WKO history written in Coggan zones, where existing notes, workouts, and conversations reference "Z3 Tempo" with Coggan band boundaries.
• Coaches whose prescription style is anchored to the Coggan model.
• Athletes whose primary cycling-coaching reference is the Coggan literature.

When to stay on Yousuli

• New athletes with no prior zone framework.
• Athletes who already follow Yousuli-anchored prescriptions (which is what the Hub's macrocycle and race-planning notes use).
• Athletes who value the 3a / 3b sweet-spot split.

Practical note for coach notes and prescription

CoachNotes are free text. If a coach writes "do 3 x 12 min in Z3b sweet spot" in a note and the athlete later switches to Coggan, "Z3b" is not a Coggan zone name. The text in the note does not auto-translate; the coach should communicate the change to the athlete or rewrite prescription text in the new system's terms.

A small migration aid: the Hub's zone glossary describes both systems side by side for translation.

See also: Zone anchor methodology, Yousuli zones explained, Coggan reference, Switching systems.