In plain English
Bands of heart rate, usually five, that divide effort from very easy to maximal. They help you keep easy days easy and hard days on target.
What it is
Heart rate zones split your working heart rate range into bands, typically five, from very easy (Zone 1) to maximal (Zone 5). Three common ways to set them:
- Percentage of maximum heart rate: each zone is a slice of your max.
- Heart rate reserve: zones are set within the range between your resting and maximum heart rate.
- Threshold-based: zones are anchored to your lactate threshold heart rate, often from a field test.
Why it matters for training decisions
Zones give each session a clear target. Studies of successful endurance athletes describe a pattern where most sessions are done at low intensity, with a smaller share of high-intensity work. Zones make that pattern easier to follow and make it easier to notice when easy days creep into “moderate”.
How wearables measure it, and the limits
Different methods, and different default formulas, put the boundaries in different places. So Zone 2 on your watch might not match Zone 2 in Strava or intervals.icu. Pick one method and stick with it.
Heart rate also lags behind effort in short intervals, drifts upwards in long or hot sessions (see cardiac drift), and optical sensors can be less reliable during strength work and sled pushes. For short, hard efforts, pace, power or perceived effort are often better guides.
Apple Watch calculates zones automatically from your health data, and lets you set them manually.
How P247 uses it
P247’s heart rate zones are off until you turn them on. When you do, P247 sets five zones from your maximum heart rate, your heart rate reserve or your threshold heart rate, or you can enter your own limits. For maximum heart rate, you choose a number you enter, a 60-second peak from your Apple Health workouts that you accept, or the Tanaka age estimate. If you already have zones in Strava, you can copy them in by hand. They aren’t imported or synced automatically.
Read more on the P247 blog
Sources
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance, 2010.
- Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology, 2001.
- Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Medicine, 2009.
- Apple Support: View Heart Rate Zones on Apple Watch.
This glossary is general information to help you understand your training data. It isn't medical advice, diagnosis or treatment. For injury, illness, medication, blood test results or any health concern, speak to a qualified health professional.
P247 turns your Apple Health data into a daily brief and a weekly report that tells you what to change next week. Launching on the App Store at the end of November 2026. Your first weekly report is free.
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