For best accuracy, measure when waking up.
Tanaka Formula
This is a rough estimate based on heart rate ratio. For clinical accuracy, a gas exchange test is required.
Zone 2 training—often called "base training"—is the intensity where your body primarily uses mitochondrial respiration (fat oxidation) rather than glycolysis (carbohydrate burning).
Practical Tip:
Zone 2 should feel like a "conversational pace"—you can speak in full sentences but would rather not. Aim for 150-180 minutes per week for maximum longevity benefits.