Build an interval session
JustZone2 isn't only for Zone 2. This is the app's Interval Builder, rebuilt for the web: set the intervals and the recovery between them, see the session's shape and how hard it is, then ride it in ERG mode on your smart trainer.
Change any setting and the session updates as you go. In the app, you save it and ride it.
How hard, and how often?
Intervals work, but more isn't better. We went through the research on how many hard sessions a week amateurs should do, and the answer is clearer than you might expect:
One hard session a week is enough to start with, or to hold fitness through a busy patch. Three belongs in a short, planned block, not every week.
Fitting it into a week? The training planner places two hard sessions 48 hours apart and fills the rest with Zone 2. For why the easy riding matters as much as the intervals, see The Rise and Reassessment of Zone 2.
What is weighted average power?
Plain average power undersells interval sessions, because hard efforts cost disproportionately more than easy riding. Take the default session above (5 × 4 minutes at 220 W) and a session of ten 30-second efforts at 350 W, both with the same warm-up and cool-down. Their average powers are almost the same, 163 W and 167 W. Their weighted average powers are 182 W and 212 W, and the second one is the session that will hurt.
Weighted average power accounts for that. It takes the session second by second, smooths it with a 30-second rolling average, raises each value to the fourth power, averages those, and takes the fourth root. The result is closer to the steady power that would feel as hard. Compare two sessions by it to see which will hurt more.
Ride it in JustZone2
- In the app (version 1.0.2 or later), go to Settings and turn on Interval Builder.
- On the Workout tab, switch to Intervals and build your session. The controls are the same as above.
- Tap Start Intervals. Your trainer holds each interval's power in ERG mode, with a countdown to every interval and the session's shape on screen.
Interval rides upload to Strava under their own name and are kept out of your Zone 2 progress charts, so a hard day never muddies your aerobic trend.
This page is a demo of the builder; nothing here is saved. Build and save your sessions in the app.
Zone 2 locked in. Intervals when you want them. On any FTMS smart trainer.
General guidance, not a personal coaching plan. If you have a medical condition, or are new to hard exercise, check with a doctor before doing high-intensity intervals.