HRV	Heart Rate Variability
CV	Coefficient of Variation
R-R Interval	Time between successive R-waves in the QRS complex of an electrocardiogram
ECG	Electrocardiogram
RMSSD	Root Mean Square of Successive R-R Differences
SDNN	Standard Deviation of Normal-to-Normal Intervals
pNN50	Proportion of R-R Intervals That Differ by >50 ms
HF	High frequency power (0.15–0.40 Hz)
LF	Low frequency power (0.04–0.15 Hz)
SD1	Short-term variability perpendicular to line of identity of a Poincaré plot
SD2	Long-term variability along the line of identity of a Poincaré plot
PSD	Power Spectral Density
n.u.	Normalized Units
PPG	Pulse Plethysmography
CI	Confidence Interval
Ln	Natural Log-Transformed
FOR	Functional Overreaching
NFOR	Non-Functional Overreaching
SS	Stress Score
SPS	Sympathetic/Parasympathetic Ratio
MSS	Modified Stress Score
MSPS	Modified Sympathetic/Parasympathetic Ratio
SRSS	Short Recovery and Stress Scale
TQR	Total Quality Recovery Scale
RESTQ-Sport	Recovery-Stress Questionnaire
GPS	Global Positioning System