Heart rate zones are defined ranges of heart rate intensity, expressed as percentages of your maximum heart rate (MHR), used to categorise and guide the intensity of exercise. Training in different zones produces different physiological adaptations, making heart rate zones a powerful framework for structuring workouts and ensuring balanced training.
The five standard zones
While zone models vary slightly between platforms, the most widely used framework divides intensity into five zones:
Zone 1: Active Recovery (50-60% MHR)
Very light effort. You can hold a full conversation easily. This zone promotes blood flow and gentle recovery without adding training stress. Walking, light stretching, and casual cycling fall here.
Zone 2: Aerobic Base (60-70% MHR)
Light-to-moderate effort. You can speak in full sentences but might pause occasionally. This is the foundation of endurance training — it builds aerobic capacity, improves fat metabolism, and strengthens the cardiovascular system without excessive fatigue. Most long, easy runs and rides should be in Zone 2.
Zone 3: Tempo (70-80% MHR)
Moderate effort. Conversation becomes difficult — you can manage short phrases. This zone improves cardiovascular efficiency and muscular endurance. It is often called the "grey zone" because it is hard enough to accumulate fatigue but not intense enough to drive maximal adaptations.
Zone 4: Threshold (80-90% MHR)
Hard effort. Speaking is limited to a few words at a time. Training near your lactate threshold improves your body's ability to sustain high-intensity effort and process lactate. Intervals, tempo runs, and competitive efforts often target this zone.
Zone 5: Maximum (90-100% MHR)
All-out effort. You cannot speak. This zone is only sustainable for very short periods (seconds to a few minutes). It develops peak power, speed, and anaerobic capacity. Sprints and maximal intervals live here.
How to determine your zones
The simplest method uses an estimated maximum heart rate: 220 minus your age. While this formula provides a rough guideline, individual variation is significant. A more accurate approach is to perform a field test (such as a maximal effort run) or use a laboratory VO2 max test. Wearables like Penng calculate your zones based on your profile data and display real-time zone information during workouts.
Why zone-based training matters
Many people default to training in Zone 3 — moderate effort that feels productive but is neither easy enough to recover from quickly nor hard enough to drive strong adaptations. The most effective training programmes deliberately polarise intensity: spending most time in Zones 1-2 (easy) and a smaller portion in Zones 4-5 (hard), with relatively little time in Zone 3.
Penng's strain score is calculated in part from time spent in each heart rate zone, giving you an objective measure of how hard your day was and whether your training intensity matches your recovery status.
Learn more about your health data — take the free quiz at penng.ai/quiz.