Heart rate variability (HRV) is the variability in the time intervals between successive heartbeats. The heart rate is
regulated by opposing forces of the nervous system: one wants to increase the heart rate in response to certain
factors (“fight or flight) and the other wants to lower the heart rate (“rest and ruminate”). Thus the heart does not
always beat at a constant rhythm. The variability in the beat-to-beat time intervals is a manifestation of the degree
of interaction between these opposing forces and is what HRV tries to capture. HRV corresponds to the body’s
ability to adapt to different physiological or environmental stimuli and as a result has become a useful tool in
understanding the athlete’s adaption to training load and recovery.1
How does Ember measure HRV?
Ember measures HRV by analyzing the variation in time between pulse rates in the plethysmograph wave form
obtained at the fingertip. The plethysmograph waveform represents the blood-volume changes that occur with each
heartbeat. A higher HRV score means that there is more variability in the beat-to-beat time period, whereas a
lower HRV means that there is less variability.
How does our approach compare to other methods?
Traditionally, HRV has been measured by analyzing the variation in time between heartbeats by examining what’s
called the “R-R” time. Simply, this is a measure derived from analysis of an electrocardiogram (ECG or EKG) which
analyzes the electrical activity of the heart.
In summary, Ember measures HRV by looking at the time variation between heartbeats by examining the
plethysmograph waveform, whereas ECG-based systems measure HRV by looking at the time variation between
heartbeats by examining electrical impulses from the heart. External and internal studies have shown a high
degree of statistical equivalence between HRV determined from the plethysmograph and ECG2,3,4
What factors influence HRV?
HRV for an individual is affected by many factors such as age, sex, and race. Additionally, lifestyle factors such
as level of physical activity and fitness, alcohol and tobacco consumption as well as, psychological factors such
as stress, depression, and negative emotions can also impact HRV.5 Values in the range of 20-70 are considered
normal for healthy adults and values trending upwards is generally considered a good measure of improving
fitness and the body’s ability to adapt to external stimuli.
The time of day when the measurement is taken and the body posture can also impact HRV. As such, like the
other Ember biomarkers, the first-of-day measurement before getting out of bed is the best time to take an HRV
How does tracking HRV and emotions help the athlete?
While studies have shown that HRV can track improving cardiovascular fitness, there’s also evidence that emotions
can impact HRV as well. Studies have shown that negative emotions such as being sad, angry, or scared cause
irregular heart rates and a reduced HRV.5 In addition, studies have shown that positive emotions can have
a positive impact on sports performance whereas negative emotions can have a negative impact on sports
performance.6 By tracking and trending Emotions and HRV with the other Ember biomarkers, you will now be
better equipped to understand how your body responds to external factors to help you better understand your
body, response to training, readiness, and more.
1. Dong, JG. The role of heart rate variability in sports physiology. Experimental and Therapeutic Medicine 11,
2. Lu G, Yang F, Taylor J, Stein, J. A comparison of photoplethysmography and ecg recording to analyse heart
rate variability in healthy subjects. Journal of Medical Engineering and Technology 33, 634–641 (2009).
3. Selvaraj N, Jaryal A, Santhosh J, Deepak KK, Anand S. Assessment of heart rate variability derived from
finger-tip photoplethysmography as compared to electrocardiography. J Med Eng Technol 32, 479-484
4. Cercacor, HRV Validation Study, Data on File, (2017).
5. Fattison J, Oswald V, Lalonde F. Influence diagram of physiological and environmental factors affecting heart
rate variability: an extended literature overview. Heart International 11, E32-E40, (2016).
6. McCarthy PJ. Positive emotion in sport performance: current status and future directions. International Review
of Sport and Exercise Psychology. 4, 50-69 (2011).
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