Heart Rate Variability (HRV), is one of the most important measurements of your heart and one of the least used in mainstream health & fitness. HRV is the measurement of time between heartbeats and can be an indicator for how your body handles stress. This could tell you if you are about to get sick, if you are training too hard, or if you are more predisposition to stress, anxiety, and even more serious conditions such as heart disease.
It is commonly understood that the heart beats consistently, much like a clock, in fact the opposite is supposed to be true. The more variable your heart beats are the more adaptable you are to stress. If your HRV is low, your body is not handling stress very well and you may need to step up those breathing exercises, focus on relaxation, recovery, and getting more restful sleep!
Though you can use a heart rate monitor for HRV, the “HRV4Training” app uses your phone’s camera and only takes 60 seconds each morning. Many wearables that have heart rate monitoring capabilities can also capture HRV, take the apple watch for example, it measures your HRV every time you put it on or when you use the watch’s native breathe app.
Article: Heart Rate vs HRV