Quantifying CNS Fatigue via HRV
Why standard resting HR is a lagging indicator, and how to use rMSSD to modulate loads.
Central Nervous System (CNS) fatigue is the primary governor of explosive performance. Yet, many coaches still rely on subjective RPE or lagging indicators like resting heart rate.
The rMSSD Metric
The Root Mean Square of Successive Differences (rMSSD) is the gold standard for parasympathetic measurement. A significant drop (>1 CV) indicates a sympathetic shift—your athlete is fried.
Intervention Protocol
If rMSSD drops > 1.5 standard deviations from the 7-day rolling average:
- Cut plyometric volume by 50%.
- Cap resistance training intensity at 75% 1RM.
- Eliminate all glycolytic conditioning.
Integrate this data with the ACWR Calculator to ensure you aren't compounding fatigue.