Zone 2 Based on LTHR vs Max HR: Which Method to Use
At 145 bpm your LTHR chart says Zone 2; your age-based Garmin chart says Zone 3+. Same athlete, 15–20 bpm of disagreement. Max HR describes a ceiling. LTHR marks where aerobic work starts costing more. For easy-day discipline, threshold-anchored zones usually match feel better than 220−age.
Two Reference Points, Different Jobs
% max HR (often 60–70% of max) is simple but loose. LTHR (e.g. Friel running Zone 2 ≈ 85–89% of LTHR) targets true base intensity below rapid lactate rise. Max-HR Zone 2 often sits lower in absolute bpm than LTHR Zone 2 — follow the low range and easy runs feel artificial.
Worked Numbers: Age 38 Athlete
Inputs: age 38, measured max HR 186, resting 52, field-test LTHR 168.
- 220−age (60–70%): ~109–127 bpm
- Measured max (60–70%): ~112–130 bpm
- Karvonen 60–70%: ~132–146 bpm
- Friel LTHR 85–89%: ~143–150 bpm
At 145 bpm, LTHR says Zone 2; age-max says Zone 3+. Compare methods in the Zone 2 Calculator and HR Zones Calculator.
Do not trust auto-detected watch LTHR after one hot, hilly long run. Auto-LTHR can lag fitness jumps or skew with heat. Retest with a controlled 30-min hard effort every 6–8 weeks in a build, and never copy bike LTHR into running zones.
Why LTHR Zone 2 Can Exceed 70% Max
If LTHR is a high fraction of max (common in trained runners), 85–89% of LTHR can sit above 70% of max. That is expected — not a bug. Still verify with the talk test: if 148 bpm is conversational and sustainable, it can be true Zone 2 even when a default chart calls it Zone 3.
Garmin Defaults Worth Fixing
Out of the box, many watches still use % max with Zone 2 = 60–70% and max = 220−age until you change them. Switch the zone basis to LTHR or %HRR in Connect/Training Hub once you have a real threshold. Treat auto-LTHR as a draft after heat or hills, then confirm with a controlled test before rewriting every easy alert.
Decision Rule
If you train by HR three or more days per week and watch “easy” conflicts with conversational feel, switch the watch zone basis to LTHR (or Karvonen with a real max) and ignore 220−age Zone 2. If you only glance at HR occasionally, a measured-max % band plus talk test is enough.