Table 2. Heart rate variability (HF, LF, LF/HF and TP) pre and post ingestion of either placebo or caffeine supplementation in able-bodied, paraplegic and tetraplegic participants in supine and sitting position.

	Placebo		Caffeine		Δ p-value
	Pre	Post	Pre	Post
HF (supine) [ms2]
AB	723 [23; 3724]	1044 [25; 7154]*	689 [171; 5862]	1442 [168; 4517]	0.31
P	239 [20; 3376]	566 [60; 6092]*	487 [27; 1767]	659 [26; 2744]	0.07
T	757 [85; 6745]	784 [247; 4265]	848 [36; 2380]	666 [211; 3598]	0.87
HF (sitting) [ms2]
AB	1005 [19; 6088]	1341 [16; 5426]	415 [56; 7119]	1110 [136; 7039]	0.75
P	162 [23; 4670]	513 [29; 6971]*	373 [34; 1882]	465 [11; 2157]	0.038§
T	323 [17; 824]	477 [251; 2877]	275 [19; 2553]	508 [222; 2595]	0.61
LF (supine) [ms2]
AB	741 [124; 2477]	900 [99; 2581]*	375 [108; 3226]	789 [135; 3604]*	0.08
P	196 [53; 1865]	564 [42; 2803]	472 [69; 1272]	200 [40; 1612]	0.07
T	151 [14; 1180]	243 [87; 1549]	673 [10; 1018]	359 [126; 588]	0.13
LF (sitting) [ms2]
AB	1064 [88; 2325]	891 [147; 3063]	747 [107; 4384]	1037 [89; 4228]	0.48
P	357 [56; 3651]	1025 [77; 3136]	432 [95, 1730]	334 [35; 2622]	0.09
T	247 [2; 1089]	363 [42; 1126]	281 [16; 967]	313 [68; 648]	0.50
LF/HF (supine)
AB	1.08 [0.17; 5.31]	0.66 [0.18; 3.90]	0.72 [0.10; 1.01]	0.65 [0.15; 2.8]	0.31
P	0.90 [0.19; 13.10]	0.70 [0.29; 6.68]	0.70 [0.46; 9.65]	0.59 [0.24; 1.80]	0.95
T	0.25 [0.17; 0.87]	0.51 [0.18; 0.70]	0.80 [0.14; 2.75]	0.43 [0.10; 1.29]	0.31
LF/HF (sitting)
AB	1.57 [0.21; 4.55]	1.21 [0.36; 9.06]	1.27 [0.29, 7.18]	0.63 [0.25; 3.81]	0.39
P	1.56 [0.60; 7.83]	1.68 [0.45; 5.06]	0.98 [0.45; 12.68]	0.57 [0.19; 6.39]*	0.37
T	0.44 [0.10; 1.41]	0.76 [0.07; 1.73]	0.83 [0.38; 1.95]	0.56 [0.13; 1.09]	0.61
TP (supine) [ms2]
AB	1591 [180; 5938]	1901 [149; 9851]*	1159 [340; 8000]	3014 [401; 8265]*	0.53
P	437 [98; 5472]	1291 [106; 8391]*	1014 [189; 3120]	934 [78; 4566]	0.038§
T	951 [104; 7970]	1320 [442; 5894]	1346 [53; 3449]	942 [358; 4000]	0.87
TP (sitting) [ms2]
AB	2158 [111; 7538]	2172 [167; 8444]	1394 [186; 11733]	2589 [264; 11739]	0.75
P	634 [88; 9462]	1946 [189; 10507]*	1094 [264; 3743]	1159 [95; 4934]	0.015§
T	663 [30; 2024]	856 [341; 4180]	611 [36; 3582]	668 [473; 3221]	0.61

AB = able-bodied participants; P = paraplegic participants, T = tetraplegic participants; HF = high frequency power; LF = low frequency power; LF/HF = ratio between LF and HF; TP = total power

* significant change from pre to post ingestion (p < 0.05)

^§ significant difference between the changes in the placebo and the caffeine trial (p < 0.05)

Δ p-value = p-value comparing the difference between pre and post measurement of the placebo trial with the difference from the caffeine trials