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Table 1 Description of extracted HRV parameters

From: Effects of different exercise interventions on heart rate variability and cardiovascular health factors in older adults: a systematic review

Variable Units Description Indicator of …
SDNN ms Standard deviation of all NN intervals total variability
RMSSD ms Square root of the mean of the sum of the squares of differences between adjacent NN intervals short-term variability
NN50 count   Number of pairs of adjacent NN intervals differing by more than 50 ms in the entire recording spontaneous variability
pNN50 % NN50 count divided by the total number of all NN intervals spontaneous variability
LF ms2 Power in low frequency range (≤ 0.04 Hz) sympathetic and parasympathetic, but predominantly sympathetic
HF ms2 Power in high frequency range (0.15–0.4 Hz) parasympathetic
LF nu   LF power in normalised units LF/(Total Power–VLF) × 100 sympathetic and parasympathetic, but predominantly sympathetic
HF nu   HF power in normalised units HF/(Total Power–VLF) × 100 parasympathetic
LF/HF   Ratio LF [ms2]/HF [ms2] sympathetic and parasympathetic
TP ms2 Total performance or total spectrum; corresponds to energy density between 0.00001 to 0.4 Hz total variability
SD1 ms Standard deviation of instantaneous beat-to-beat variability, extracted from Poincaré Plot parasympathetic
SD2 ms Standard deviation of the long-term variability, extracted from Poincaré Plot sympathetic and parasympathetic
  1. HF (nu), power in high frequency range (in normalized units); Hz, Hertz; LF (nu), power in low frequency range (in normalized units); ms, millisecond; NN50, number of pairs of adjacent NN intervals differing by more than 50 ms in the entire recording; pNN50, number of pairs of adjacent NN intervals differing by more than 50 ms in the entire recording divided by the total number of all NN intervals; RMSSD, square root of the mean of the sum of the squares of differences between adjacent NN intervals; SD1, standard deviation of instantaneous beat-to-beat variability, extracted from Poincaré Plot; SD2, standard deviation of the long-term variability, extracted from Poincaré Plot; SDNN, standard deviation of NN intervals. Modified Sammito & Böckelmann [55].