ICC analysis for non-normalised data of static postures

a) EMG signal cleaned by the manual ECG cleaning technique

After visual inspection of the ECG artefact and ECG cleaning, RMS values for the cleaned data (the uncontaminated EMG signal) for all electrode sites for all 20 subjects were calculated. The ICC was used to examine the reliability (between different days of recording) of the surface EMG signal for all electrode sites.

The results of the ICC for the four point kneeling postures are summarised in Table 3 – 5. The four point kneeling posture with the left arm raised flexion to 90 degrees (4PL) had more electrode sites demonstrating good reliability (ICC ≥ 0.75) when compared to the other four point kneeling postures (Table 3 – 5). For these postures, only one electrode site had good reliability.

Table 3 – 5 : ICC for four point kneeling posture with respect to RMS of the signal cleaned by the manual ECG cleaning technique

Electrode site ICC good reliability (ICC ≥ 0.75). L2/3 L : lumbar 2/3 Iliocostalis muscle. L2/3 M : lumbar 2/3 superficial multifidus muscle. L4/5 M : lumbar 4/5 superficial multifidus muscle. 4PL refers to four point kneeling with the left arm raised flexion to 90 degrees. 4PN refers to four point kneeling with no arms raised. 4PR refers to four point kneeling with the right arm raised flexion to 90 degrees.

The results of the ICC for sitting posture group are summarised in Table 3 – 6. Sitting with one arm raised flexion to 90 degrees (SITL and SITR) had more electrode sites demonstrating

good reliability (ICC ≥ 0.75) when compared with the sitting posture with no arms (SITN) or bilateral arms raised flexion to 90 degrees (SITB). For these postures only two electrode sites had good reliability (ICC ≥ 0.75).

Table 3 – 6 : ICC for sitting postures with respect to RMS with respect to RMS of the signal cleaned by the manual ECG cleaning technique

Electrode site ICC

SITB SITL SITN SITR

L2/3 L 0.733 0.835‡ 0.709 0.672

L2/3 M 0.507 0.775‡ 0.655 0.825‡

Right

L4/5 M 0.569 0.715 0.283 0.475

L2/3 L 0.843‡ 0.906‡ 0.916‡ 0.914‡

L2/3 M 0.824‡ 0.903‡ 0.813‡ 0.871‡

Left

L4/5 M 0.741 0.826‡ 0.161 0.847‡

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). L2/3 L : lumbar 2/3 iliocostalis muscle. L2/3 M : lumbar 2/3 superficial multifidus muscle. L4/5 M : lumbar 4/5 superficial multifidus muscle. SITB refers to sitting with bilateral arms raised flexion to 90 degrees. SITL refers to sitting with the left arm raised flexion to 90 degrees. SITN refers to sitting with no arms raised. SITR refers to sitting with the right arm raised flexion to 90 degrees.

The results of the ICC for standing posture group are summarised in Table 3 – 7. Standing posture with one arm raised flexion to 90 degrees (STANL and STANR) had more electrode sites demonstrating good reliability (ICC ≥ 0.75) than the standing posture with no arms raised (STAN) or bilateral arms raised flexion to 90 degrees (STANB). For standing posture with no arms raised (STAN), there were no electrode sites demonstrating good reliability (ICC ≥ 0.75).

Table 3 – 7 : ICC for standing posture with respect to RMS with respect to RMS of the signal cleaned by the manual ECG cleaning technique

Electrode site ICC

STAN STANB STANL STANR

L2/3 L 0.304 0.366 0.615 0.458

L2/3 M 0.529 0.609 0.805‡ 0.796‡

Right

L4/5 M 0.647 0.859‡ 0.907‡ 0.878‡

L2/3 L 0.714 0.395 0.689 0.888‡

L2/3 M 0.687 0.673 0.829‡ 0.749

Left

L4/5 M 0.634 0.871‡ 0.885‡ 0.814‡

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). L2/3 L : lumbar 2/3 iliocostalis muscle. L2/3 M : lumbar 2/3 superficial multifidus muscle. L4/5 M : lumbar 4/5 superficial multifidus muscle. STAN refers to standing with no arms raised to 90 degrees. STANB refers to standing with bilateral arms raised flexion to 90 degrees. STANL refers to standing with the left arm raised flexion to 90 degrees. STANR refers to standing with the right arm raised flexion to 90 degrees.

Static postures (including four point kneeling, sitting, and standing) with no arms raised had the poorer reliability of the surface EMG signal than posture with one arm or bilateral arms raised flexion to 90 degrees for each posture. Only standing posture with one arm raised flexion to 90 degrees (STANL and STANR) had good reliability (ICC ≥ 0.75) with respect to the medial muscle groups including L2/3 and L4/5 superficial multifidus muscles.

b) EMG signal cleaned by the semi-automatic ECG cleaning technique

When the raw data was cleaned by the manual ECG removal, for five of the static postures at least three electrode sites had good reliability (ICC ≥ 0.75) with respect to RMS values. The raw data of these postures which was taken from a 10 second recording was cleaned by the semi-automatic ECG cleaning technique (Please see section 3.2.6. b) Semi-automatic ECG cleaning technique, Page 88).

The ICC was used to determine the reliability (between different days of recording) of the amplitude and frequency of the signal for each electrode site. The value 0.75 was adopted as an acceptable level of reliability. The results of the ICC analysis for these electrode sites are summarised in Tables 3 – 8 and 3 – 9.

For the amplitude of the signal, standing with the left arm raised flexion to 90 degrees (STANL) had more electrode sites which had good reliability (ICC ≥ 0.75) when compared with the other four postures. Three electrode sites had good reliability (ICC ≥ 0.75) for the four point kneeling with the left arm raised flexion to 90 degrees (4PL), and the sitting with the left arm raised flexion to 90 degrees (SITL). The sitting posture with the right arm raised flexion to 90 degrees (SITR) had two electrode sites which had good reliability (ICC ≥ 0.75).

There was no electrode site which had good reliability (ICC ≥ 0.75) for the standing posture with the right arm raised flexion to 90 degrees (STANR).

Table 3 – 8 : ICC with respect to RMS of the signal cleaned by the good reliability (ICC ≥ 0.75). L2/3 L : lumbar 2/3 iliocostalis muscle. L2/3 M : lumbar 2/3 superficial multifidus muscle. L4/5 M : lumbar 4/5 superficial multifidus muscle. 4PL refers to four point kneeling with left arm raised flexion to 90 degrees. SITL refers to sitting with the left arm raised flexion to 90 degrees. SITR refers to sitting with the right arm raised flexion to 90 degrees. STANL refers to standing with the left arm raised flexion to 90 degrees. STANR refers to standing with the right arm raised flexion to 90 degrees.

For mean frequency, only one electrode site had good reliability (ICC ≥ 0.75) for standing posture with the left arm raised flexion to 90 degrees (STANL). Furthermore, for other postures all electrodes sites had poor reliability (ICC < 0.70).

Table 3 – 9 : ICC with respect to mean frequency of the signal cleaned by the semi-automatic ECG cleaning technique good reliability (ICC ≥ 0.75). L2/3 L : lumbar 2/3 iliocostalis muscle. L2/3 M : lumbar 2/3 superficial multifidus muscle. L4/5 M : lumbar 4/5 superficial multifidus muscle. 4PL refers to four point kneeling posture with the left arm raised flexion to 90 degrees. SITL refers to sitting posture with the left arm raised flexion to 90 degrees. SITR refers to sitting posture with the right arm raised flexion to 90 degrees. STANL refers to standing posture with the left arm raised flexion to 90 degrees.

STANR refers to standing posture with the right arm raised flexion to 90 degrees.

3.3.5. Reliability of recorded surface EMG of the lumbar paraspinal