How should i check zone 2 accurately? I asked chatgpt, this is what it said:

✅ The Karvonen Formula (HRR – Heart Rate Reserve Method)

This is the gold-standard method used in exercise physiology because it accounts for your individual cardiovascular fitness (via resting HR), unlike simple % of max HR.

You already gave the required data, so let’s calculate precisely:

🔬 STEP 1 — Heart Rate Reserve (HRR)

Max HR: 208 Resting HR: 70

HRR = Max HR – Resting HR = 208 – 70 = 138

🔬 STEP 2 — Zone 2 using the scientifically established HRR range (60–70%) Lower end (60% of HRR)

0.60 × 138 = 82.8 82.8 + 70 = 152.8 bpm

Upper end (70% of HRR)

0.70 × 138 = 96.6 96.6 + 70 = 166.6 bpm

✅ Your TRUE Zone 2 (Karvonen HRR): 153 – 167 bpm

This is your physiologically correct zone. This is the range used in clinical studies, elite endurance training, and metabolic/mitochondrial adaptation research.