rMSSD (Root Mean Square of Successive Differences) measures short-term heart rate variability (HRV) by analyzing fluctuations between consecutive heartbeats. It reflects the balance between sympathetic and parasympathetic nervous system activity.
Step-by-Step Calculation of rMSSD
Example RR Intervals (ms):
1000, 950, 1020, 960, 990
1. Find the Differences Between Consecutive RR Intervals:
950 - 1000 = -50
1020 - 950 = 70
960 - 1020 = -60
990 - 960 = 30
Differences: -50, 70, -60, 30
2. Square Each Difference:
(-50)² = 2500
(70)² = 4900
(-60)² = 3600
(30)² = 900
Squared differences: 2500, 4900, 3600, 900
3. Find the Mean of the Squared Differences:
(2500 + 4900 + 3600 + 900) / 4 = 2975
4. Take the Square Root of the Mean:
√2975 = 54.58 ms
Thus, in this example, rMSSD = 54.58 ms, representing short-term heart rate variability.
How to Measure rMSSD
To measure rMSSD, SDNN, and BPM, athletes must use a Polar H10 heart rate strap.