How does the biofeedback score work?

​The score in the app represents how well you are practicing deep breathing according to your resonant frequency, as well as the duration of the exercise. You will see that if you are not focused in your session, or struggle to perform the exercise correctly, the score will not increase much over time. On the other hand, correctly following the pacer and deep breathing, will lead to a higher score over time. In general, the higher the score, the better

While the score is provided so that you can quantify the exercise, note that what matters the most in this case is the deep breathing exercise itself, and how  this might impact your baseline physiology

GETTING TECHNICAL

In a little more detail, we currently compute the biofeedback score as follows. We first collect data for the entire duration of your session. Then, we compute the power spectrum by first ​interpolating the peak to peak differences (PP or RR intervals) at 4Hz. This step is necessary as RR intervals obviously are not evenly spaced in time, and we need evenly spaced data in order to perform frequency domain analysis. Once we have re-sampled our data, we remove the DC component, convert into seconds, and compute a hamming windowing on the time series we've got from previous steps. After windowing, we compute the FFT and then determine the power in the low frequency (LF) band, which is the main band of interest for biofeedback. Why is that? Because when deep breathing, we increase power in this window, since any breathing rate between about 4.5 to 8.5 breaths / minute, will result in a frequency inside the LF band 

At this point, once we have the LF power, we also multiply this score for the duration of the session, and then by a linear factor which allows the score to be a bit more user friendly. The whole point of this procedure is to have a score that capture well the deep breathing exercise and the fact that a longer session is beneficial (more training!)

Below you  can see an example of a power spectrum for a session of 3 minutes, you can see quite clearly how the LF band contains a large peak, which was the breathing rate of this session (6 breaths / minute, or 0.1 Hz)