Stay in Your Target Zone with Real-Time Audio Cues.

ZoneTrainer gives you instant voice reminders and audio alerts the moment you drop below or exceed your target heart rate zone. Train hands-free without looking at your phone.

🛡️ 100% Offline & Private 📡 Universal BLE Support ⚡ 100% Free Core Features 📊 TCX & CSV Export

Baseline Formula

Max HR (220 − Age)

The traditional Fox & Haskell formula provides an instant estimate of your physiological ceiling based on chronological age.

Formula: Max HR = 220 − Age. Zones scale from 50% to 100% of maximum heart rate.
Best For: Fitness beginners seeking a fast, hassle-free baseline without physical threshold testing.
Consideration: Does not reflect individual resting heart rate or athletic adaptations (can vary by ±10–12 BPM).

Personalized Range

Karvonen (Heart Rate Reserve)

Calculates target zones by measuring your Heart Rate Reserve (HRR), combining both resting heart rate and maximum heart rate.

Formula: Target HR = (HRR × % Intensity) + HR_rest, where HRR = HR_max − HR_rest.
Best For: Consistent runners and cyclists whose resting HR drops as cardiovascular conditioning improves.
Advantage: Dynamically adjusts your target zones to reflect true physiological effort and aerobic fitness gains.

Endurance Standard

LTHR (Joe Friel 30-Min Test)

Anchors training zones around your Lactate Threshold Heart Rate — the maximum intensity sustainable before rapid blood lactate accumulation.

How to Measure: Run or cycle a 30-minute solo time trial at maximum race pace. Your average HR of the final 20 minutes is your LTHR.
Best For: Competitive endurance athletes, marathon runners, and triathletes training for peak threshold performance.
Advantage: Eliminates statistical guesswork by directly calibrating zones to your actual metabolic inflection points.

🏃 Zone 2 Science

Practical Guidelines for Zone 2 Aerobic Base Building

Why Zone 2 is the Foundation of Endurance

Zone 2 training (typically 60–70% Max HR or 69–83% LTHR) stimulates mitochondrial biogenesis, enhances capillary density, and trains muscle fibers to utilize fat as their primary fuel source. Regular Zone 2 volume builds an enormous aerobic engine while minimizing central nervous system fatigue.

Mitochondrial Biogenesis: Expands mitochondrial volume to generate ATP oxidatively.
Lactate Clearance: Trains Type I slow-twitch muscle fibers to recycle lactate efficiently.
Sustainable Recovery: High aerobic volume with minimal orthopedic strain and low fatigue accumulation.

How to Stay in True Zone 2 Hands-Free

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The "Talk Test" (Conversational Pace): You should be able to speak complete sentences comfortably without gasping for air (RPE 3–4 out of 10).

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Steady Nasal Breathing: You should maintain continuous nasal inhales without feeling air-starved or forced mouth breathing.

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Preventing "Zone Creep" with Real-Time Audio Cues: Heart rate naturally drifts upward during long sessions (cardiac drift) or on slight hills. ZoneTrainer's instant voice reminders immediately alert you when you drift out of Zone 2, so you can adjust your pace hands-free without looking at your phone.