Heart Rate Zones: The Complete Guide

Training "by feel" works for a while, but to progress sustainably you need to know at what intensity you're working. Heart rate (HR) zones are the simplest tool for that.

Why think in zones?

Each zone solicits different energy systems: base endurance develops your aerobic engine and durability, threshold improves sustainable pace, maximal intensity works VO2max. Mixing without logic = stagnation. Dosing = progress.

The 5 classic zones

• Zone 1 (recovery): very easy, easy conversation. Active recovery.
• Zone 2 (endurance): easy, you can speak in sentences. This is where the bulk of fitness is built.
• Zone 3 (tempo): "moderately hard". Use with caution, this is the zone where many get stuck.
• Zone 4 (threshold): hard, sustainable ~20-60 min. Improves race pace.
• Zone 5 (VO2max): very hard, in short intervals.

How to calculate your zones?

The "220 - age" formula for max HR is very approximate. Better to start from your threshold HR (the HR sustained over ~1h of intense effort), measured during a field test or deduced from your races. Zones are then calculated as percentages of this threshold HR — that's what tools like Intervals.icu do.

The distribution that works: 80/20

High-performing endurance athletes spend about 80% of their time in zone 1-2 (easy) and 20% at intensity (zone 4-5), avoiding getting stuck in zone 3. See our article on 80/20 polarization.

HR or power/pace?

HR has a lag (it rises slowly, drifts with heat and fatigue). For short intense efforts, pace (running) or power (cycling) are more reactive. The ideal is to use both. Understanding fitness and fatigue with CTL/ATL/TSB.

Zones updated automatically

Sports Coach AI reads your threshold HR from your data (Garmin, Intervals.icu), calculates your zones and builds sessions that respect the right distribution — without you having to do the math.