Paraspinal strength and electromyographic fatigue in patients with sub-acute back pain and controls: Reliability, clinical applicability and between-group differences

Table 3 Mean ± SD values on 2 separate days for initial median frequency, median frequency-slope and root mean square for the isometric endurance test in both groups

	Healthy (n = 26)			LBP (n = 66)
Parameter	Day 1	Day 2	P value	Day 1	Day 2	P value
IMF (Hz)
L2/3 R	60.3 ± 10.9	61.0 ± 11.1	0.48	66.5 ± 17.6	66.1 ± 15.8	0.82
L2/3 L	58.2 ± 9.0	59.1 ± 12.3	0.52	63.5 ± 17.2	61.9 ± 13.2	0.18
L4/5 R	89.3 ± 20.3	91.0 ± 16.4	0.49	83.2 ± 24.3	83.0 ± 21.3	0.89
L4/5 L	90.9 ± 20.1	92.3 ± 17.3	0.59	82.7 ± 26.0	83.5 ± 20.8	0.59
L2/3	59.24 ± 9.7	60.1 ± 11.4	0.44	65.0 ± 16.4	64.0 ± 13.8	0.39
L4/5	90.1 ± 19.4	91.6 ± 15.9	0.49	82.9 ± 24.3	83.2 ± 20.0	0.83
MF slopes (raw, Hz/s)
L2/3 R	-0.30 ± 0.14	-0.35 ± 0.12	0.02a	-0.12 ± 0.16	-0.12 ± 0.17	0.77
L2/3 L	-0.30 ± 0.11	-0.31 ± 0.10	0.52	-0.10 ± 0.18	-0.11 ± 0.14	0.41
L4/5 R	-0.48 ± 0.16	-0.54 ± 0.22	0.19	-0.23 ± 0.25	-0.22 ± 0.20	0.62
L4/5 L	-0.56 ± 0.21	-0.61 ± 0.19	0.19	-0.21 ± 0.25	-0.23 ± 0.25	0.53
L2/3	-0.30 ± 0.11	-0.33 ± 0.10	0.08	-0.11 ± 0.16	-0.11 ± 0.15	0.51
L4/5	-0.52 ± 0.17	-0.57 ± 0.19	0.13	-0.22 ± 0.23	-0.22 ± 0.20	0.84
MF slopes (normalised, %/min)
L2/3 R	-28.8 ± 11.5	-31.5 ± 9.0	0.14	-9.0 ± 15.2	-9.9 ± 15.8	0.55
L2/3 L	-29.9 ± 9.3	-29.8 ± 8.4	0.95	-8.1 ± 15.9	-10.5 ± 14.8	0.11
L4/5 R	-34.0 ± 11.3	-34.2 ± 11.9	0.90	-15.0 ± 15.7	-15.0 ± 12.0	0.98
L4/5 L	-36.4 ± 10.7	-37.7 ± 10.4	0.58	-13.2 ± 14.0	-17.1 ± 13.3	0.01a
L2/3	-29.3 ± 9.8	-30.6 ± 7.9	0.39	-8.6 ± 14.8	-10.2 ± 14.5	0.21
L4/5	-35.2 ± 9.6	-36.0 ± 10.2	0.67	-14.1 ± 13.7	-16.1 ± 11.7	0.10
RMS slopes (normalised, %/min)
L2/3 R	43.4 ± 45.0	37.4 ± 35.2	0.35	10.4 ± 21.4	11.3 ± 18.5	0.72
L2/3 L	27.4 ± 30.8	29.0 ± 28.3	0.73	11.3 ± 17.3	13.9 ± 22.8	0.17
L4-5 R	42.6 ± 35.9	32.7 ± 29.2	0.19	14.3 ± 21.2	12.6 ± 22.2	0.43
L4/5 L	37.1 ± 36.2	38.4 ± 34.1	0.85	10.3 ± 19.3	13.9 ± 21.2	0.07

^aP < 0.05.

Hz: Hertz; IMF: Initial median frequency; MF: Median frequency; RMS: Root mean square.