Table 2.

Results of heart rate variability assessment of the study groups, before and after intervention with strength training

Variable	CON (n = 10)		p-value	HI (n = 10)		p-value	BFR (n = 12)		p-value	p-value
	Before	After		Before	After		Before	After		Δ Comparisons
Heart rate variability
HR (bpm)	62 ± 10	63 ± 8	0.40	71 ± 11	68 ± 14	0.28	65 ± 10	65 ± 10	0.47	0.76
RR interval (ms)	987.5 ± 160.8	964.7 ± 130.4	0.28	861.3 ± 141.5	907.7 ± 163.4	0.23	938.8 ± 142.4	933.8 ± 138.7	0.45	0.61
SDNN (ms)	23.1 [15.7–50.5]	18.3 [11.0–40.6]	0.08	23.1 [14.4–33.3]	19.5 [ 14.0–23.2]	0.28	18.7 [15.5–25.9]	21.9 [13.5–28.1]	0.41	0.36
rMSSD (ms)	25.2 [14.9–35.8]	23.7 [10.3–48.1]	0.19	23.7 [13.3–40.0]	23.1 [13.0–28.8]	0.43	20.9 [13.0–33.8]	22.7 [14.2–32.0]	0.47	0.95
pNN50 (%)	4.1 [0–14.3]	3.5 [0–22.0]	0.26	5.6 [0.3–19.8]	2.1 [0.2–5.5]	0.30	0.8 [0.1–9.3]	1.5 [0.1–10.6]	0.25	0.63
LF (n.u.)	51.6 ± 24.3	49.2 ± 29.4	0.35	58.5 ± 22.5	43.9 ± 22.5	0.07	50.3 ± 18.9	49.0 ± 18.6	0.37	0.29
HF (n.u.)	48.3 ± 24.3	50.7 ± 29.4	0.35	41.5 ± 22.5	56.1 ± 22.4	0.07	49.6 ± 18.8	50.9 ± 18.5	0.38	0.29
LF:HF ratio	0.77 [0.46–3.42]	0.88 [0.28–3.54]	0.25	1.63 [0.99–3.31]	0.59 [0.35–2.33]	0.12	1.24 [0.56–1.87]	0.91 [0.61–1.71]	0.43	0.30
Total power (ms2)	802.0 ± 869.7	751.8 ± 811.5	0.28	682.5 ± 714.2	675.5 ± 1223.1	0.25	570.3 ± 718.4	514.8 ± 415.8	0.78	0.78

Mean ± SD; median: [percentiles 25–75]); CON – control; HI – high intensity; BFR – blood flow restriction; HR – heart rate; BPM – beats per minute; RR interval – average of all normal R-R intervals; SDNN – standard deviation of all normal NN interval; rMSSD – root- mean of square sucessive NN interval difference; pNN50 – percent of normal-normal NN intervals whose difference exceeds 50 ms; LF – low frequency band; HF – high frequency band; LF:HF ratio – sympathovagal balance; Δ comparisons tested by one-way ANOVA.