# Feature request: Native Heart Rate Reserve (%HRR / Karvonen) heart-rate zones

**URL:** <https://forum.intervals.icu/t/feature-request-native-heart-rate-reserve-hrr-karvonen-heart-rate-zones/132356>\
**Category:** Feature Requests\
**Created:** [9 September 2026 19:42 UTC](https://forum.intervals.icu/t/feature-request-native-heart-rate-reserve-hrr-karvonen-heart-rate-zones/132356 "2026-09-09T19:42:02Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![MedTechCD](https://forum.intervals.icu/user_avatar/forum.intervals.icu/medtechcd/32/40383_2.png) [@MedTechCD](https://forum.intervals.icu/u/MedTechCD)\
**Post date:** [20 September 2026 14:09 UTC](https://forum.intervals.icu/t/feature-request-native-heart-rate-reserve-hrr-karvonen-heart-rate-zones/132356/4 "2026-09-20T14:09:01Z")

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> [@Custom zones for sports](https://forum.intervals.icu/t/custom-zones-for-sports/114875/1):
>
> - Zones based on any standard anchor (FTP, LTHR etc.) as well as custom activity fields and absolute values

Make a Custom field that calculates HRR based on HRmax and HRrest for the day of the activity and then use that Custom activity field as anchor.  
Any change in HRmax and/or HRrest will be accounted for.  
Look at the script of underneath Custom Field to get you started

 ![image](https://forum.intervals.icu/uploads/default/original/3X/4/2/4278dbd7fd4c84e23a48208fe81cf48ebbef7247.png)

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