Heart Rate Zones & VO2 Max
What the zones actually mean, and why most of your running should feel embarrassingly easy.
Training zones are typically defined as percentages of max heart rate or heart rate reserve: Zone 1-2 (easy/recovery), Zone 3 (moderate/tempo), Zone 4 (threshold), Zone 5 (VO2 max/anaerobic). The exact percentages vary by method, but the practical takeaway is consistent: most of your weekly volume should sit in Zone 1-2.
This surprises people. The 80/20 principle — roughly 80% of training time easy, 20% moderate-to-hard — shows up again and again in research on endurance athletes. Running everything at a moderate effort (the most common mistake) builds fatigue without building much fitness.
VO2 max — the maximum rate your body can use oxygen — is one input into performance, not the whole story. It responds well to short, hard intervals (Zone 5), but running economy, lactate threshold, and durability matter just as much for race results, and those develop through consistent volume, not just hard efforts.
If you don't have a heart rate monitor, effort-based zones work fine: Zone 2 should let you hold a full conversation; threshold pace is 'comfortably hard' — sustainable for about an hour; VO2 max efforts should feel unsustainable past 3-8 minutes.
This is educational content, not medical advice — talk to a doctor about anything specific to your health or an existing injury.