Heart Rate Variability (HRV)

Heart rate varies with every heartbeat. Heart rate variability (HRV) is the variation of beat to beat intervals, also known as R-R intervals. Electrocardiogram (ECG) is the electric signal originating from heart. The most distinct feature of the ECG is the QRS complex, which consists of the Q, R and S waves and originates from the electrical activation of the heart ventricles. Figure 1 illustrates the variation of time between R-R intervals.

Heart Rate Variability (HRV) graph illustrating the variation of beat to beat intervals.
Figure 1. Variation of beat to beat intervals, also known as R-R intervals.

HRV indicates the fluctuations of heart rate around an average heart rate. An average heart rate of 60 beats per minute (bpm) does not mean that the interval between successive heartbeats would be exactly 1.0 sec, instead they may fluctuate/vary from 0.5 sec up to 2.0 sec.

HRV is affected by aerobic fitness. HRV of a well-conditioned heart is generally large at rest. Other factors that affect HRV are age, genetics, body position, time of day, and health status. During exercise, HRV decreases as heart rate and exercise intensity increase. HRV also decreases during periods of mental stress. HRV is regulated by the autonomic nervous system. Parasympathetic activity decreases heart rate and increases HRV, whereas sympathetic activity increases heart rate and decreases HRV.

HRV is used in the OwnIndex, Ownzone, OwnOptimizer, OwnRelax and EnergyPointer features. It can also be monitored on its own using the training computer. If your HRV changes at a given pace and heart rate, this may indicate a change in your training load and stress.