Heart Rate Variability Logger is an application that lets you record, plot and export time (AVNN, SDNN, rMSSD, pNN50) and frequency (LF,HF,LFHF) domain Heart Rate Variability Features.

Heart Rate Variability Logger requires a Bluetooth Low Energy (also called Bluetooth Smart or BLE or 4.0) heart rate sensor (tested with: Polar H7, mio alpha and Armour39)

Extracted and stored features:
- Heart rate,
- R-R intervals,
- 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),
- Low to High frequency power ratio (LFHF).

The time window used to compute features can be configured choosing between 30 seconds, 1 minute or 5 minutes.

Heart Rate Variability can be indicative of overtraining, stress level, as well as relaxation. Generally speaking, once you've been able to determine your baseline, you should see reduced heart rate variability (in terms of both time - e.g. SDNN - and frequency - e.g. HF - domain features) due to overtraining or higher mental or physical stress. On the other hand HRV will tend to improve with higher relaxation state.

Other features:
- Events recording
- Upload to your Dropbox