HRV, or heart rate variability, is the variation in the time interval between two successive heartbeats. It is a measure of the autonomic nervous system's (ANS) influence on the heartbeat. The ANS regulates the sympathetic and parasympathetic activity of the heart, which affects heart rate.

HRV is used as a marker of stress and recovery. A high HRV indicates a low level of stress and a higher ability to recover from exercise. A low HRV indicates a high level of stress and a lower ability to recover from exercise.

HRV is influenced by many factors, including age, fitness level, and lifestyle. It is important to note that HRV is not the same as heart rate. Heart rate is the number of times your heart beats per minute. HRV is a measure of the variation in time between each heartbeat.

HRV is a useful tool for athletes and coaches to monitor training load and recovery. It can also be used to monitor general stress levels and recovery from illness or injury.

There are a number of ways to measure HRV. The most common method is to use a heart rate monitor to record the time interval between each heartbeat over a period of time. HRV can also be measured using an electrocardiogram (ECG).

HRV measures can be affected by many factors, including how active you are, how rested you are, what you have eaten, and how much caffeine or alcohol you have consumed. It is important to take these factors into account when interpreting HRV measures.