Insights & biomarkers

Heart Rate Variability

Heart Rate Variability, or HRV for short, is a non-invasive measure of your autonomic nervous system, which is the body’s main control center. It is widely considered as one of the best objective metrics for physical fitness and determining your body’s readiness to perform. HRV is literally the variance in time between the beats (NN interval) of your heart. 
How is it calculated?
A commonly used statistical metric for representing short-time HRV (over a time duration of the order of 10s to 1 min) is the Standard Deviation of NN intervals (SDNN). It quantifies the variability between successive normal-to-normal (NN) intervals, which are the time intervals between consecutive heartbeats. In this case, PPG signals are used to extract the NN intervals. Starting from PPG signals, the following steps are executed to determine the SDNN value:
PPG signal preprocessing
Systolic peak detection
NN interval calculation
SDNN calculation
The definition and additional contextual information of each output is outlined below in the table.

How can it be used? 
HRV is a valuable metric for assessing stress levels or recovery after sports. When a person has a low HRV, it indicates a high activity of the sympathetic nervous system (SNS), which is associated with stress, overwhelm and arousal.
Assessing the HRV at rest can provide valuable personalized insights into:
Quantifying the chronical stress level.
Scoring sleep quality and total wellbeing of the person. A reduction in HRV will be visible when sleep quality is reduced.
The impact of unhealthy food or low nutritions. 
The quality and effects of recovery exercises. Engaging in activities that aim to increase HRV and restore the balance of the autonomic nervous system (ANS) can be beneficial for recovery. The metric should be carefully measured and controlled to ensure the positive effect of the training and the needed personalized durations.
Use HRV as a powerful metric to assess body stress load during a health check-in. Provide personalized recommendations based on the corresponding score level. 
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Insights
SDNN is returned as an integer on a scale of 0 - ∞ as a part of the output response JSON, with the key sdnn.

Output (milliseconds)
Definition
Example Color Indicator
Example User Text
0 - 35
Below average
Red
Your heart rate variability value is below average. This indicates your body is under pressure for some reason which could be due to exercise, psychological proceedings or any other external and internal stressors.
36 - 100 
Average - Healthy
Yellow
Your heart rate variability is in a normal range. To further increase your heart rate variability you can perform aerobic and/or breathing exercises or meditation.
>100
Above average – Excellent
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Green
Your heart rate variability is above average which general states that the body has a stronger capability to cope up with stress or is recovering strongly from previously built-up stress.
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Respiratory Rate

ANS Balance

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TABLE OF CONTENTS

How is it calculated?

How can it be used?

Insights

Output (milliseconds)	Definition	Example Color Indicator	Example User Text
0 - 35	Below average	Red	Your heart rate variability value is below average. This indicates your body is under pressure for some reason which could be due to exercise, psychological proceedings or any other external and internal stressors.
36 - 100	Average - Healthy	Yellow	Your heart rate variability is in a normal range. To further increase your heart rate variability you can perform aerobic and/or breathing exercises or meditation.
>100	Above average – Excellent	Green	Your heart rate variability is above average which general states that the body has a stronger capability to cope up with stress or is recovering strongly from previously built-up stress.