ICC analysis for normalised data

a) EMG signal cleaned by the manual ECG cleaning technique

After manual removal of the ECG artefact, the RMS values for the cleaned data (the uncontaminated EMG signal) for all 20 subjects were calculated using a one-second data sample. The RMS was normalised relative to one electrode site (Left lumbar 4/5 superficial multifidus muscle) (Left L4/5 M) of the medial muscle group. The ICC was examined for reliability (between different days of recording) of the surface EMG signal for each ratio.

The results of the ICC analysis of the normalised amplitude of the cleaned signal for all the four point kneeling postures are summarised in Table 3 – 13. The four point kneeling posture with the left arm raised flexion to 90 degrees (4PL) had good reliability (ICC ≥ 0.75) for one

electrode site. However, for the other four point kneeling postures there was poor reliability (ICC < 0.75) for three ratios.

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). 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 analysis of the normalised amplitude of the cleaned signal for all sitting postures are summarised in Table 3 – 14. For the sitting posture group with bilateral arms raised flexion to 90 degrees (SITB), no electrode sites had good reliability (ICC ≥ 0.75). The sitting posture with no arms raised (SITN) or one arm raised flexion to 90 degrees (SITL and SITR) had good reliability (ICC ≥ 0.75) for at least one of three electrode sites.

Table 3 – 13 : ICC of normalised signal cleaned by the manual ECG cleaning technique for four point kneeling posture

Ratio ICC

Refer to Left L4/5 M 4PL 4PN 4PR

Ratio 1 Right L2/3 M 0.804‡ 0.256 0.354

Ratio 2 Right L4/5 M 0.726 0.213 -0.160

Ratio 3 Left L2/3 M 0.730 0.600 -0.158

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). 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 analysis of the normalised amplitude of the cleaned signal for all standing postures are summarised in Table 3 – 15. For the standing posture with the left arm raised flexion to 90 degrees (STANL), all three electrode sites had good reliability (ICC ≥ 0.75). In contrast, the other three standing postures had good reliability (ICC ≥ 0.75) for at least one electrode site.

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). 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. 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.

Table 3 – 14 : ICC of normalised signal cleaned by the manual ECG cleaning technique for sitting posture

Ratio ICC

Refer to Left L4/5 M SITB SITL SITN SITR

Ratio 1 Right L2/3 M 0.232 0.864‡ 0.656 0.680

Ratio 2 Right L4/5 M 0.385 0.714 0.244 0.514

Ratio 3 Left L2/3 M 0.504 0.489 0.818‡ 0.751‡

Table 3 – 15 : ICC of normalised signal cleaned by the manual ECG cleaning technique for standing posture

Ratio ICC

Refer to Left L4/5 M STAN STANB STANL STANR

Ratio 1 Right L2/3 M 0.280 0.647 0.800‡ 0.573 Ratio 2 Right L4/5 M 0.081 0.855‡ 0.872‡ 0.725 Ratio 3 Left L2/3 M 0.776‡ 0.751‡ 0.780‡ 0.802‡

In this analysis for normalised data, only two static postures: four point kneeling with the left arm raised flexion to 90 degrees (4PL) and standing with the left arm raised flexion to 90 degrees (STANL) had good reliability (ICC ≥ 0.75) for all electrode sites.

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

In this analysis, only non-normalised data which demonstrated good reliability of static postures after manual ECG cleaning were analysed. Therefore, a total five static postures were analysed including 4PL, SITL, SITR, STANL, and STANR. After semi-automatic ECG cleaning of the signal recorded during maintenance of these postures, RMS value was calculated for all electrode sites. These RMS values were then normalised relative to the one reference electrode site (Left lumbar 4/5 multifidus muscle) (Left L4/5 M) as previously described (Please see Section 3.2.7. Normalising data, Page 90 – 91). The results of the ICC analysis for normalised data are summarised in Table 3 – 16.

Table 3 – 16 : ICC of normalised signal cleaned by the semi-automatic ECG cleaning technique

Ratio ICC

Refer to Left L4/5 M 4PL SITL SITR STANL STANR

Ratio 1 Right L2/3 M 0.851‡ 0.877‡ 0.468 0.691 0.707

Ratio 2 Right L4/5 M 0.651 0.841‡ 0.483 0.744 0.641

Ratio 3 Left L2/3 M 0.814‡ 0.440 0.390 0.720 0.569

"ICC" refers to Intraclass correlation coefficient. All values reported are ICC values. "‡" indicates good reliability (ICC ≥ 0.75). L2/3 M : to lumbar 2/3 superficial multifidus muscle. L4/5 M : to lumbar 4/5 superficial multifidus muscle. 4PL refers to four point kneeling with the 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.

Four point kneeling posture with the left arm raised flexion to 90 degrees (4PL), and the sitting posture with the left arm raised flexion to 90 degrees (SITL) demonstrated good reliability overall electrode sites.

3.4. Discussion

The aim of this experiment was to determine the reliability of the surface EMG signal to measure low back muscle activity during maintenance of the simple static postures on two different days.