The Android Zone 2 & Heart Rate Audio Coach.

ZoneTrainer gives you real-time voice alerts the moment you drift outside your target heart rate zone. Train hands-free on Android without constantly checking your phone screen.

Google Play Store Direct APK Download
✓ 100% Offline & Private • ✓ Universal BLE Support • ✓ 100% Free Core • ✓ TCX & CSV Export
🫀 Physiological Progression Engine

Measure True Cardiovascular Fitness Without GPS or Cloud Subscriptions.

Heart rate alone doesn't tell you if you're getting fitter. ZoneTrainer's Zone 2 Benchmark correlates your aerobic base pace with average heart rate to calculate metabolic adaptations over time — completely offline on your device.

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Zone 2 Base Pace

Quantifies pace (min/km or min/mi) at strictly aerobic Zone 2 intensity across a 12-month season.

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Efficiency Factor (EF • m/min/bpm)

Measures horizontal distance covered per heartbeat (m/min/bpm or yd/min/bpm) compared against a rolling 10-run baseline.

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Aerobic Decoupling (Pw:HR)

Compares 1st vs 2nd half efficiency with automatic 10-minute warmup clipping to isolate true steady-state cardiac drift.

Get ZoneTrainer on Google Play View Sample HTML Report ↗
Aerobic Efficiency & Decoupling +8.8% EF vs last 10 runs
1.27 m/min/bpm
Z2 Pace: 5:42/km (@ 138 bpm) • Pw:HR Drift: 2.4% Coupled (10m warmup clipped)
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100% On-Device Standalone HTML Export Open Report →

Free Online Zone 2 Athletic Tools

Instant, client-side tools designed for runners and cyclists. 100% private with zero data sent to external servers.

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Zone 2 & HR Zone Calculator

Calculate your personalized training zones using Karvonen Heart Rate Reserve (HRR), Tanaka, or Lactate Threshold (LTHR). Includes a comprehensive physiological guide and zone breakdowns.

Calculate Your Zones →
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Strava & TCX Training Audit

Drag & drop your Strava export archive or TCX runs to diagnose your "Black Hole" training distribution, calculate your Aerobic Efficiency Factor (EF), and generate reports.

Launch Audit Tool →

Engineered for Privacy & Performance

Everything you need for precise zone training without unnecessary cloud clutter or vendor lock-in.

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100% Offline & Private

Your heart rate and workout logs never leave your device. Zero accounts, zero tracking, zero external network requests.

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Universal BLE Support

Seamlessly pair locally with Polar H10, Garmin HRM, Wahoo TICKR, CooSpo, Magene, and standard BLE heart rate monitors (GATT 0x180D). Note: Apple, Galaxy & Pixel watches do not broadcast open BLE standard profiles natively.

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Phrase-Aware Audio & Ducking

Instant voice reminders whenever you drift in or out of your target zone, with automatic dynamic media ducking for music and podcasts.

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AudioTrack PCM Metronome

Sample-accurate (±0.02ms) high-cadence audio metronome running on a dedicated low-latency stream for running and cycling cadence.

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TCX & CSV Fitness Export

Export your sessions to standard Garmin TCX (compatible with Strava & Garmin Connect) or CSV directly through Android Storage Access Framework.

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Full JSON Backup & Restore

Complete offline data portability. Export and restore all your sessions, custom interval programs, and zones with zero cloud dependency.

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Zone 2 Aerobic Benchmark

Track long-term base pace evolution, cardiac cost (HR × min/km), and Aerobic Efficiency Factor (EF). Export interactive standalone HTML reports with Chart.js curves.

📊 Explore Live Demo Report ↗
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Interactive Telemetry Graph

Detailed post-workout cardiovascular canvas with stepped target corridors, live touch scrubber, target compliance ribbons, and cardiac drift analysis.

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Dark Sports-Tech UI

Cohesive dark slate glass styling (#0F172A), high-contrast metric chips, and precision monospace typography built for glanceability during intense workouts.

App Screenshots

Clean, distraction-free UI built specifically for active workouts.

Active Workout Gauge (In Zone) Screen
Live Telemetry (In Zone)

High-contrast gauge displaying real-time heart rate, % HRmax, dynamic in-zone teal highlight, & audio status.

Active Workout Alert (Out of Zone) Screen
Dynamic Theme (Out of Zone)

Adaptive UI shift and instant directional voice cue the moment your heart rate drifts above or below your target zone.

Structured Interval Workout HUD Screen
Structured Interval HUD

Follow built-in or custom interval programs with real-time target zone locking, interval countdown, and step progress.

Post-Workout Recap and Compliance Screen
Telemetry & Compliance

Inspect interactive heart rate curves, target corridors, cardiac drift, and zone distribution with instant TCX/CSV exports.

Training History and 8-Week Volume Chart Screen
Zone 2 Benchmark & History

Review your rolling Zone 2 pace, aerobic efficiency factor (EF), aerobic density, and 8-week training volume at a glance.

Physiological Zone Calculation Methods Screen
3 Physiological Methods

Calculate precise heart rate training zones using Fox (220 - Age), Karvonen (HRR), or Lactate Threshold (LTHR).

Zone 2 Aerobic Benchmark Standalone HTML Dashboard
Standalone HTML Benchmark

Generate self-contained, privacy-first interactive HTML dashboards complete with Chart.js pace & efficiency curves. Open Live Demo Report ↗

Supported Bluetooth LE Hardware

Compatible with standard GATT Heart Rate Service (0x180D) Bluetooth LE devices. Connects 100% locally with zero cloud dependencies.

Polar
Polar H10, H9, Verity Sense, OH1

Industry-standard ECG chest straps & optical sensors verified for flawless offline Bluetooth LE connectivity.

Garmin
Garmin HRM-Pro, HRM-Dual, HRM-Fit

Premium chest strap heart rate monitors broadcasting standard Bluetooth LE HR telemetry.

Wahoo
Wahoo TICKR & TICKR X

Dual-band Bluetooth LE chest strap monitors with instant local pairing and high accuracy.

CooSpo
CooSpo H6, H808S, H9Z

Affordable, reliable Bluetooth LE chest straps delivering precise real-time heart rate data.

Magene & Scosche
Magene H64/H303, Rhythm+ 2.0

Popular dual-protocol chest straps and optical forearm sensors with rock-solid BLE streaming.

Universal BLE Monitors
Chest Straps & Smartwatches

Seamless compatibility with Huawei Watch, Garmin, and any BLE sensor broadcasting standard heart rate profile.

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Support Independent Development

ZoneTrainer is 100% free, private, and ad-free. If ZoneTrainer improves your athletic training, consider supporting ongoing development with a coffee!

☕ Support on Ko-fi 💬 Send Feedback