HRV4Training vs Rhythm SYNC.
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
HRV4Training
Quantify stress, balance training and lifestyle, and improve performance with scientifically validated heart rate variability insights. This app accurately assesses HRV using your phone's camera or compatible devices, offering actionable interpretations for optimizing your training plan.
- HRV-based stress quantification
- Training and lifestyle balance
- Performance improvement insights
- Camera-based HRV assessment
- Integration with wearables
- Training load analysis
- VO2max and Lactate Threshold estimation
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The first scientifically validated Heart Rate Variability (HRV) app. HRV4Training provides HRV based insights to help you quantify stress, better balance training and lifestyle, and improve performance. HRV4Training does not require a heart rate monitor, since it can accurately assess your HRV using the phone's camera. HRV4Training also works with Apple Watch, the Oura ring and all compatible Bluetooth SMART sensors. HRV4Training is also the first app that goes beyond simple measurements and provides insights on: 1) acute or day to day HRV changes in response to different stressors (alcohol, travel, sick days, training, menstruation, etc.) 2) long term multi-parameter trends to look at the big picture 3) correlations between physiological measurements and annotations 4) training load analysis, fitness, fatigue, readiness to perform and injury risk 5) VO2max estimation for runners linking the app to Strava or TrainingPeaks and using a heart rate monitor during their workouts 6) Training Polarization analysis (or 80/20) 7) Lactate Threshold Estimation for runners linking the app to Strava or TrainingPeaks and using a heart rate monitor during their workouts 8) Weekly and monthly summaries to track progress. All data is processed inside the app in order to provide you with actionable interpretations that can help optimizing your training plan and performance. Supported devices for the camera measurement: iPhones 5, 5S, 6, 6S, 6+, 6S+, SE, 7, 7+, 8, 8+, X, XS, XS Max, XR, 11, 11 Pro, 11 Pro Max, 12 mini, 12, 12 Pro, 12 Pro Max, 13 mini, 13, 13 Pro, 13 Pro Max, 14, 14 Plus, 14 Max, 14 Pro, 15, 15 Max, 15 Pro, 16, 16 Max, 16 Pro Currently unsupported devices for the camera measurement: iPhones 4S, iPads and iPods - These devices require a chest strap. Other features: - HRV-based advice helps you to adapt your trainings based on objective measures of recovery - TAGS: lets you tag your sleep, mental energy, muscle fatigue, stress and all other parameters that can help you understand what is influencing your physical condition and physiological stress - Works with Bluetooth SMART heart rate monitors (a Polar H7 is recommended) or simply your phone's Camera - Integrates with the Health app (writes heart rate, and sleep, read sleep time) - Configurable test (single or orthostatic, choose test duration between 1, 3 or 5 minutes) - Extracts and stores the following features while lying down and/or standing: heart rate, mean of beat-to-beat intervals (AVNN), standard deviation of beat-to-beat intervals (SDNN), square root of the mean squared difference of successive R-Rs (rMSSD), number of pairs of successive R-Rs that differ by more than 50 ms (pNN50), low frequency power (LF, 0.04-0.15 Hz), high frequency power (HF, 0.15-0.40 Hz) - Shows the PPG signal view to ensure signal quality during the test if the camera is used instead of a bluetooth SMART sensor - HRV4T Recovery Points to provide a single, straightforward metric to analyze your physical condition - Population summaries and people like you comparisons to put your data into perspective - Analysis of compliance and consistency - Data export via email or Dropbox - Integrates with TrainingPeaks, Oura, Strava and Coros HRV4Training requires to register an account with your email address, so that your data can be backed up safely and retrieved in case anything happens (app issue, changing phone, etc.). HRV4Training does not provide medical advice. It is intended for informational purposes only. Consult a medical professional before making health or lifestyle decisions. Please find an overview of the relevant scientific literature in our guide, here: https://marcoaltini.substack.com/p/the-ultimate-guide-to-heart-rate
Rhythm SYNC.
This app connects to heart rate monitors to display real-time data, manage activity modes, and track workout history. It allows for software updates and integrates with HealthKit for saving workout data.
- Connects to Rhythm 24 and Rhythm+ monitors
- Manages activity modes and biometrics
- Displays heart rate and battery level
- Configures data sharing with other apps
- Collects and downloads recorded activities
- Performs software and firmware updates
- HealthKit integration
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The award-winning Rhythm Heart Rate Monitors use patented technology to capture exceptionally accurate performance in both wet and dry conditions. This Scosche Rhythm Sync app: · Connects to Rhythm 24 and Rhythm+ Heart Rate Monitors · Manages Rhythm 24 activity modes and biometrics functionality: Heart Rate Only, Running, Cycling, Swimming, Heart Rate Variability, Duathlon, and Triathlon · Displays heart rate data from your Rhythm Monitors · Displays Rhythm battery level · Configures sharing with compatible heart rate tracking apps, fitness watches, bike computers, and fitness equipment, to stream your fitness-data in real time, track heart rate history, and more! · Collects Rhythm 24 recorded activities and has download capabilities · Allows for Rhythm Heart Rate Monitors software and firmware updates · HealthKit integration which allows you save workout data recorded on the sensor.
Screenshots
Verdict
The clearest difference is review sentiment: HRV4Training at 61% against Rhythm SYNC.'s 13%. HRV4Training also leads on rating (3.6 vs 1.8) and chart position (#10 vs unranked). Rhythm SYNC.'s advantage is price (Free vs $9.99) and iOS requirement (12.0 vs 15.6). On ratings volume, update cadence, ads and in-app purchases there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Rhythm SYNC. is free to download; HRV4Training costs $9.99 up front. Neither carries in-app purchases, so what you see is what you pay.
HRV4Training holds the better App Store score, 3.6 against 1.8. Both are backed by a comparable volume of ratings — 288 and 128 respectively. Written reviews point the same way: 61% of HRV4Training's written reviews are positive against 13% of Rhythm SYNC.'s.
HRV4Training ships an update every 6 weeks, Rhythm SYNC. every 3 months. The most recent releases landed on September 24, 2026 and September 3, 2026 respectively.
| Parameter | HRV4Training | Rhythm SYNC. |
|---|---|---|
| Price | $9.99 | Free — better |
| Rating | 3.6 (288 ratings) — better | 1.8 (128 ratings) |
| Positive reviews | 61.2% of reviews — better | 13.1% of reviews |
| Number of ratings | 288 — better | 128 |
| Update frequency | Every 6 weeks — better | Every 3 months |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | Free — better |
| Best chart rank | #10 — better | — |
| Devices | iPhone, iPod | iPhone, iPod |
| Requires iOS | 15.6 | 12.0 — better |
| Further details — not scored | ||
| Size | 35 MB | 47 MB |
| Age rating | 4+ | 4+ |
| Developer | A.S.M.A. B.V. | Scosche |
Customer experience
HRV4Training
Rhythm SYNC.
User reviews
HRV4Training
From 288 App Store ratingsWhat we love
- 👍 Accurate HRV measurements
- 🚀 Straightforward and easy to use
- 💡 Provides valuable insights for training and recovery
- 👍 Integrates well with other fitness apps
- 👍 Responsive and helpful developer support
Room to improve
- 🐛 Inconsistent readings and technical issues
- 🔒 Requires user account and data sharing
- 🔒 Concerns about data privacy
- 🔋 Drains battery when using camera for measurements
Rhythm SYNC.
From 128 App Store ratingsWhat we love
- ✅ Accurate heart rate readings
- 🔋 Long-lasting device battery life
- 🔄 Reliable device hardware
- 📱 Simple and straightforward interface
- 🔗 Works well with third-party apps (Peloton, Garmin, Apple Watch)
Room to improve
- 🐛 Frequent Bluetooth connection failures
- 🐛 App crashes and freezes regularly
- ❌ App doesn't recognize connected devices
- ⚠️ HRV mode difficult or impossible to access
- 📊 Extremely limited app functionality
Bugs and requests
HRV4Training
Reported bugs
3 issues- App crashes frequently, especially with iOS updates
- Syncing issues with Strava, TrainingPeaks, and Apple Health
- Camera-based measurements often unreliable or inconsistent
Requested features
4 requests- Allow multiple measurements per day
- Improve integration with Apple Watch and other wearables
- Add more customization options and data visualization
- Expand support for non-athletic use cases
Rhythm SYNC.
Reported bugs
17 issues- App fails to detect device despite Bluetooth connection
- Bluetooth connection drops frequently during workouts
- App crashes on startup (splash screen freeze)
- Firmware update fails repeatedly
- HRV readings not displaying or accessible
Show 12 moreShow fewer
- Custom heart rate zones not applied to recordings
- Battery level shows as zero or incorrect
- Settings menu items non-functional or unresponsive
- App loses connection when device syncs with other apps
- Data disappears when monitor disconnects
- Export to CSV ignores custom zones
- App crashes when attempting to share workout data
- Last mode setting not remembered between sessions
- Unable to modify personal details (height, weight, birthday)
- Incompatibility with iPhone X and newer models
- Firmware update window won't open
- App incompatible with iOS 11 and newer versions
Requested features
12 requests- HRV (Heart Rate Variability) mode that actually works
- Comprehensive workout history and logging
- Data export to multiple health apps (MyFitnessPal, TrainingPeaks, etc.)
- Customizable heart rate zones that persist
- Batch download and export of multiple files
Show 7 moreShow fewer
- Auto-sync feature when device is detected
- Detailed analytics and charts
- Better user profile settings (height, weight, age)
- Dark mode option
- Improved troubleshooting and help documentation
- Ability to delete saved connections to health apps
- Support for multiple languages in documentation
In-app purchases
HRV4Training
No in-app purchases
Rhythm SYNC.
No in-app purchases









