NEW v2.5 Zone 2 Aerobic Benchmark Engine & Standalone Reports →

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.

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.

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Aerobic Efficiency Factor (EF)

Speed ÷ Heart Rate. Tracks how much work you produce per heartbeat.

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Cardiac Cost & Drift

Heart Rate × Pace. Directly measures cardiovascular decoupling.

🔬 Audit Your Strava History ↗ 📊 Explore Live Demo Report ↗ Get ZoneTrainer Free
Aerobic Efficiency Progression +8.8% EF
5:42 min/km
Base pace improved from 6:15/km @ 138 bpm
W1
W3
W6
W9
W12
100% On-Device Standalone HTML Export Open Report →

Interactive Heart Rate Zone Calculator

Calculate your training zones instantly using Age, Karvonen (HRR), or Lactate Threshold (LTHR) formulas.

Heart Rate Zone Formulas & Aerobic Guide

Understand the science behind Max HR, Karvonen (HRR), and LTHR (Friel) to build an unbreakable aerobic base.

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) + HRrest, where HRR = HRmax − HRrest.
  • 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.

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 any standard BLE heart rate sensor.

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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!

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