Table 7.

Main frequency-domain HRV features reported across studies.

Parameter	Studies	Percentage
HF/HF-HRV / HFA	22	91.7%
LF/LF-HRV	16	66.7%
LF/HF ratio	10	41.7%
Total power (TP)	12	50.0%
VLF	6	25.0%

HF, high-frequency power (typically 0.15–0.40 Hz), commonly associated with parasympathetic (vagal) activity; LF, low-frequency power (0.04–0.15 Hz), reflecting combined sympathetic and parasympathetic influences; LF/HF, ratio between low and high-frequency components, often interpreted as an index of sympathovagal balance; TP, total power of the HRV spectrum; VLF, very-low-frequency power (< 0.04 Hz); HFA, high-frequency activity.