Privacy Policy

1. Overview

MARCWILLS HRVA ("the App") is a heart rate variability (HRV) analyzer for sport science research and wellness monitoring. This Privacy Policy explains what data the App collects, how it is used, and how it is stored.

2. Data We Collect

2.1 Subject Information

When you register a research subject, the App collects:

• Name or anonymized subject code
• Age
• Biological sex (Male / Female)
• Resting heart rate (measured within the App or entered manually)

This information is stored in a local SQLite database on your device.

2.2 Physiological Data

During a recording session, the App collects the following data from a Polar H10 chest belt sensor via Bluetooth:

• Heart rate (bpm)
• RR intervals (ms) — beat-to-beat intervals used for HRV analysis
• ECG waveform (raw electrical signal at 130 Hz) — displayed only, not exported
• Accelerometer data (X, Y, Z axes in mg) — for motion detection and activity monitoring

This data is stored as local files in the App's private document folder on your device.

2.3 Session Configuration Data

In Activity Mode, the App additionally records:

• Target intensity settings (Karvonen % HRR, tolerance, intensity standard)
• Heart rate zone adherence data (time in range, underload, overload)
• Notification preferences for the session

This configuration is saved in a karvonen_config.md file within the session folder.

2.4 Derived Metrics

The App calculates and stores HRV metrics derived from the above data:

• RMSSD, SDNN, pNN50, Mean RR
• SD1, SD2, SD1/SD2 ratio (Poincaré plot parameters)
• ln(RMSSD), lnRMSSD/mRR (log-transformed HRV indices)
• LF Power, HF Power, LF/HF ratio, Total Power (frequency-domain, Stationary Mode only)

3. How We Use Your Data

All collected data is used solely for the following purposes:

• Displaying real-time physiological metrics during a recording session
• Storing session records for later review and export
• Generating HRV analysis reports and session summaries
• Providing intensity guidance feedback in Activity Mode

The App does not use your data for advertising, profiling, or any purpose other than the research or wellness workflow described above.

4. Data Storage

All data is stored locally on your device in:

• A SQLite database file (sdms.db) in the App's private storage
• Session folders in the App's document directory, named in the format:
  SubjectName_YYYY-MM-DD_HHMMSS_stationary/ or _activity/

The developer does not have access to this data. The data is not backed up to any cloud service by the App itself.

5. Session Output Files

Each session produces the following local files:

Stationary Mode

• hr_log.csv — timestamped heart rate log
• rr_log.csv — RR interval log
• acc_log.csv — accelerometer data log
• hrv_rolling.csv — per-minute HRV snapshot (16 columns)
• session_methods.md — analysis method documentation

Activity Mode

All files above, plus:

• activity_log.csv — per-beat intensity status log
• karvonen_config.md — session Karvonen configuration

6. Data Sharing and Export

The App does not automatically share any data with third parties. You may choose to export session data using Android's Share Sheet. This export is entirely user-initiated and the developer has no involvement in or access to exported files.

7. Permissions

Bluetooth (BLUETOOTH_SCAN, BLUETOOTH_CONNECT)

Required to scan for and connect to the Polar H10 sensor via Bluetooth Low Energy. No Bluetooth data is transmitted to external servers.

Location (ACCESS_FINE_LOCATION)

Android requires this permission for BLE scanning on Android 6.0 and above. The App does not collect, use, or store your geographic location.

Vibration (VIBRATE)

Used to provide intensity feedback notifications during Activity Mode sessions (underload and overload alerts). This is a normal Android permission and does not require user confirmation at runtime.

8. Data Retention and Deletion

You are in full control of your data:

• Delete a session: Use the delete button in the Session screen. All session files are permanently removed.
• Discard after recording: Choosing "Discard" after stopping a session permanently deletes all files from that session.
• Delete a subject: Removes all sessions and files associated with that subject.
• Uninstall the App: Removes all App data from your device.

9. Children's Privacy

This App is intended for use by researchers and professionals aged 18 and above. When subjects include minors, the researcher is responsible for obtaining appropriate informed consent in accordance with applicable laws and institutional ethics guidelines.

10. Security

All data is stored in the App's private storage directory, which is not accessible to other apps on your device (standard Android sandboxing).

11. Changes to This Privacy Policy

This Privacy Policy may be updated from time to time. Any changes will be reflected in the "Last updated" date at the top of this document.

---

Contact

For questions or concerns about this Privacy Policy, contact:
Kukuh Pambuka Putra
Developer, MARCWILLS
Email: kukuh.pambuka@outlook.com