This page explains the heart rate variability (HRV) values displayed in Breath Ball. For details on how breathing influences HRV, see the section Heart-coherent breathing: The link between breathing and heart rate variability.
For easier navigation, here are the links to the individual sections:
Disclaimer: Breath Ball is a wellness app and is intended solely for relaxation and self-observation. Breath Ball is not a medical diagnostic or treatment tool. If you have a medical condition or wish to use your heart rate variability to assess your health, consult a doctor or healthcare professional beforehand. You use Breath Ball at your sole responsibility.
What is heart rate variability (HRV)?
Heart rate variability (HRV) describes the variation in time intervals between consecutive heartbeats. A healthy heart rhythm does not maintain a rigid frequency but fluctuates dynamically, depending on physical and mental states.
A high HRV is associated with good physical fitness, lower stress levels, and better adaptability of the autonomic nervous system. Conversely, a low HRV may indicate chronic stress, exhaustion, or impaired cardiovascular health.
Explanation of the displayed values
Breath Ball displays various HRV values to analyze heart rate variability. This section gives a brief overview of the definition and interpretation of each of these values.
Source: Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in public health, 5, 258. https://doi.org/10.3389/fpubh.2017.00258
HR (Heart Rate)
Definition: Number of heartbeats per minute (bpm).
Interpretation: A low resting heart rate (60–80 bpm) is often a sign of cardiovascular fitness, while an elevated heart rate (>90 bpm) can be associated with increased stress or poorer health.
Note: Since the curves of HR (Heart Rate) and RR (Interbeat Interval – IBI) run in exactly opposite directions (if one increases, the other decreases), they exclude each other in the chart, so that only one of the two curves is shown at a time.
RR (Interbeat Interval – IBI)
Definition: Time between two consecutive heartbeats (ms).
Interpretation: Longer RR intervals correspond to a lower heart rate (e.g. during resting phases), shorter RR intervals indicate a higher heart rate.
Note: Since the curves of RR (Interbeat Interval – IBI) and HR (Heart Rate) run in exactly opposite directions (if one increases, the other decreases), they exclude each other in the chart, so that only one of the two curves is shown at a time.
Stress
Definition: Coherence of the heart rate with the breathing rate, scaled from 0 to 100.
Interpretation: A low value indicates a strong adaptation of the heart rate to breathing (coherence) and thus a deep state of relaxation. A high value indicates low synchronization between the heart and breathing rhythm.
Note: The stress value is strongly dependent on 10 second (0.1 Hz) breathing rhythms. For further information see: Heart-coherent breathing: The link between breathing and heart rate variability (HRV).
SDNN (Standard Deviation of NN Intervals)
Definition: Standard deviation of the RR intervals (ms), measures both sympathetic and parasympathetic activity.
Interpretation: Lower values indicate poor autonomic regulation, higher values are typical for healthy people.
Note: Displayed in real time during breathing exercises if enabled at the Pro settings. Disabled by default.
RMSSD (Root Mean Square of Successive Differences)
Definition: Root of the mean of the squared differences between consecutive RR intervals (ms), mainly measures parasympathetic activity.
Interpretation: A higher value (≥ 30 ms) indicates strong parasympathetic activity, while values below 20 ms are often associated with stress or poor health.
Note: Displayed in real time during breathing exercises if enabled at the Pro settings. Enabled by default.
PNN50 (%)
Definition: Percentage of RR intervals that differ by more than 50 ms.
Interpretation: Higher values (≥ 10-20%) indicate good vagal regulation, while lower values indicate impaired autonomic control.
Note: Displayed in real time during breathing exercises if enabled at the Pro settings. Disabled by default.
VLF (Very Low Frequency, 0.0033-0.04 Hz)
Definition: Energy content in very low frequencies of the HRV.
Interpretation: Associated with metabolic processes and the autonomic nervous system. Persistently low values can indicate inflammation and heart problems.
Note: Frequencies are displayed in either % (default) or ms² depending on the “HRV frequency units” setting at the Pro screen.
LF (Low Frequency, 0.04-0.15 Hz)
Definition: Energy content in the low frequency range of HRV.
Interpretation: Influenced by the sympathetic nervous system and the baroreflex. A high LF value can indicate stress or an active adaptability.
Note: Frequencies are displayed in either % (default) or ms² depending on the “HRV frequency units” setting at the Pro screen.
HF (High Frequency, 0.15-0.40 Hz)
Definition: Energy content in the high frequency range of HRV.
Interpretation: Represents parasympathetic activity. High HR values indicate a good ability to relax, low values indicate stress or poor vagal control.
Note: Frequencies are displayed in either % (default) or ms² depending on the “HRV frequency units” setting at the Pro screen.
LF/HF
Definition: Ratio between LF and HF values.
Interpretation: A high value (> 3) indicates a dominance of the sympathetic nervous system (stress), while a low value (< 1.5) indicates a parasympathetic dominance. However, this interpretation is controversial in science. See The effects of breathing on VLF, LF, HF, and the LF/HF ratio below for details.
Note: Displayed in real time during breathing exercises if enabled at the Pro settings. Disabled by default.
Acceleration
Definition: Acceleration of the heart rate (ms).
Interpretation: Indicates the change in heart rate compared to the previous heartbeat.
Note: When displayed on the chart, Acc. (Acceleration) and Dec. (Deceleration) are linked together.
Deceleration
Definition: Slowing of the heart rate (ms).
Interpretation: Indicates the change in heart rate compared to the previous heartbeat.
Note: When displayed on the chart, Dec. (Deceleration) and Acc. (Acceleration) are linked together.
The effects of breathing on VLF, LF, HF, and the LF/HF ratio
Heart rate increases during inhalation and decreases during exhalation — an effect known as Respiratory Sinus Arrhythmia (RSA), which has a significant impact on HRV.
When breathing at a steady rate of around six breaths per minute (0.1 Hz), the heart rate synchronizes with the breathing rhythm, creating a feeling of deep relaxation. This state is commonly referred to as cardiac coherence.
From a technical point of view, what’s happening is that the energy distribution in the heart rate power spectrum becomes concentrated around 0.1 Hz. Below are two screenshots showing the heart rate power spectrum during stress (left) and during cardiac coherence (right):
The red curve shows the power distribution of the heart rate signal. The blue area represents a breathing rhythm of five seconds inhaling and five seconds exhaling (0.1 Hz). During coherence (right screenshot), the heart rhythm shows a strong and narrow peak at 0.1 Hz with no major peaks in other frequency ranges. When the red and blue curves align at 0.1 Hz, it indicates strong resonance between heart rate and breath, i.e. coherence.
Because the breathing rate strongly influences the distribution of HRV power — especially in the LF and HF bands — values like LF power, HF power, and the LF/HF ratio become less reliable for assessing sympathovagal balance during paced breathing. This is especially true during cardiac coherence, where a high LF/HF ratio can appear even in a deeply relaxed state due to enhanced parasympathetic activity and baroreflex resonance.
Interactive display of values
By tapping on a value (e.g. SDNN or RMSSD), the corresponding curve can be shown or hidden.
This makes it easier to follow the development of certain parameters during the measurement.
Standard values and their dependence on age and gender
HRV values vary depending on age and gender. The following table shows the average values of the HRV metrics and their standard deviations (SD), which were collected in a study of 1906 healthy subjects aged 25 to 74 years.
Source: Voss A, Schroeder R, Heitmann A, Peters A, Perz S (2015) Short-Term Heart Rate Variability-Influence of Gender and Age in Healthy Subjects. PLOS ONE 10(3): e0118308. https://doi.org/10.1371/journal.pone.0118308
| Age | RR ± SD | SDNN ± SD | RMSSD ± SD | PNN50 ± SD | LF ± SD | HF ± SD | LF/HF ± SD |
| 25-34 | 939 ± 129 | 50.0 ± 20.9 | 39.7 ± 19.9 | 0.20 ± 0.17 | 242 ± 325 | 133 ± 174 | 2.79 ± 3.20 |
| 35-44 | 925 ± 138 | 44.6 ± 16.8 | 32.0 ± 16.5 | 0.13 ± 0.15 | 191 ± 206 | 89 ± 118 | 3.62 ± 3.73 |
| 45-54 | 923 ± 134 | 36.8 ± 14.6 | 23.0 ± 10.9 | 0.06 ± 0.08 | 113 ± 141 | 41 ± 49 | 4.10 ± 3.48 |
| 55-64 | 904 ± 123 | 32.8 ± 14.7 | 19.9 ± 11.1 | 0.04 ± 0.07 | 80 ± 103 | 29 ± 38 | 4.17 ± 3.60 |
| 65-74 | 906 ± 123 | 29.6 ± 13.2 | 19.1 ± 10.7 | 0.04 ± 0.07 | 70 ± 112 | 22 ± 29 | 4.77 ± 5.34 |
Gender differences
Differences between men (♂) and women (♀) are particularly present at a younger age – young women tend to have slightly higher parasympathetic HRV values (e.g. RMSSD, pNN50, HF) and a lower LF/HF ratio than men of the same age.
These gender differences largely equalize from around the fifth decade of life.