What is SDNN?
SDNN (standard deviation of all normal-to-normal RR intervals) is a comprehensive HRV metric capturing overall autonomic variability over a recording period. It is used in clinical cardiology and long-term stress and health assessments.
What is RMSSD?
RMSSD (root mean square of successive differences) is the primary HRV metric reflecting short-term autonomic nervous system activity. It is the most widely used HRV measure in wearable fitness devices, sports science, and cardiac health monitoring.