Final answer:
Heart rate variability (HRV) is the variation in the time between heartbeats. It is influenced by factors such as physical activity, stress, and autonomic nervous system activity. HRV can be measured using methods like electrocardiography (ECG).
Step-by-step explanation:
The variation in the time between heartbeats is referred to as heart rate variability (HRV). HRV is the measure of the beat-to-beat changes in heart rate. It is influenced by factors such as physical activity, stress, and autonomic nervous system activity.
For example, during times of stress or physical exertion, the heart rate may increase, resulting in less variability between heartbeats. On the other hand, during periods of relaxation or deep breathing, the heart rate may decrease, leading to more variability in the time between heartbeats.
HRV can be measured using various methods, including electrocardiography (ECG). Understanding HRV can provide insights into the functioning of the autonomic nervous system and overall cardiovascular health.