What Peak Intervals is
From the developer's own App Store listing, read on 3 September 2026. See the listing →
- Guided Norwegian 4×4 workouts with Apple Watch support.
- Target zone guidance at 90–95% of estimated maximum heart rate.
- Time-in-zone, repeatability across intervals, and recovery metrics.
- Trends with plain-language verdicts such as “Improving” or “Fatigued”.
- Reads workouts and heart rate from Apple Health.
Where NTRVL differs
It needs iOS 26. We run on iOS 17.
Peak Intervals lists iOS 26.0 as its minimum. That rules out every iPhone that cannot take iOS 26. NTRVL runs on iOS 17 and later, which is roughly an iPhone 8 and newer.
We work with no heart rate sensor at all.
Train by Feel runs the full protocol on the clock and tells you how hard each phase should feel. You get a session and a record; you do not get zone accuracy, and the app says so rather than showing you a zero.
You can try the whole idea for free, without a trial.
NTRVL has a free twelve-minute session — one interval, warm-up and cool-down included — that never expires. Peak Intervals offers a two-week free trial of the subscription instead. Different bets: theirs gives you everything briefly, ours gives you one real thing forever.
Either device can run the session.
Start on the phone or on the watch; the other one follows and says which is which. If your AirPods come out mid-workout, the watch takes over as the sensor without stopping the session.
When Peak Intervals is the better choice
We would rather you use the right app than ours.
- You are already on iOS 26 and want two weeks of unrestricted access to judge an app, rather than one free session.
- You prefer a single subscription tier with no free/paid line running through the app.
The numbers
| Fact | NTRVL | Peak Intervals |
|---|---|---|
| Price | Free · Pro $1.99/mo or $9.99/yr, 7 days free | Free · subscription, 2-week trial |
| On the App Store since | 16 May 2026 | 5 February 2026 |
| Latest version | 1.1 — 31 Aug 2026 | 1.2.5 — 12 Aug 2026 |
| Ratings | No ratings yet | No ratings yet |
| Minimum iOS | iOS 17.0 | iOS 26.0 |
Every figure above was read from Apple's App Store listing data on 3 September 2026. Prices and versions change — check the store before you decide.
Verdict
These two apps are trying to do the same thing and neither has a user review yet. If you are on iOS 26, install both — theirs gives you two weeks of everything, ours gives you a free session that never expires, and a fortnight is long enough to tell which one you actually open.
Try NTRVL freeThe free session is one interval, about twelve minutes, and it does not expire. No heart rate hardware required.