Tukuk-OS💓 HR Zones
ℹ️ What this tool does & how it works
The famous %HRmax method is the rough one: two people with the same max but different fitness share zones it calls equal. Karvonen fixes this with heart-rate reserve — target = resting + intensity × (max − resting) — so zones scale with cardiovascular fitness. Max HR uses the meta-analysed Gellish formula (207 \u2212 0.7 × age); the textbook 220 \u2212 age is shown for comparison because its ±10\u201312 bpm error is why percentages-of-max drift. Zone boundaries are the standard five-band convention (50\u201360 \u2026 90\u2013100% HRR).
The 220-minus-age problem
The famous 220 \u2212 age rule was never really derived \u2014 it looks like a rough 1970s sketch with no published methodology behind it, and the meta-analysis that did have data (Gellish et al., 2007) landed on 207 \u2212 0.7·age, with a ±10 bpm individual scatter that no formula removes. Percentages-of-max then compound the error: a 12 bpm wrong max shifts your "70% zone" by 8 bpm. Karvonen\u2019s reserve method, formalised in 1957, anchors the bottom of the scale to your measured resting rate instead \u2014 the number that is personal and improves with training, which is why athletes watch resting HR like a dashboard light.