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Signed Ranks test with listwise exclusion was performed to determine if there were differences among the mean ranks (means) of the CSA of the m. multifidus at each spinal region. The grouping provided two values (left and right) for each participant (n = 5) at each spinal region; thus 10 paired values for analysis (n = 10) at each spinal region. No statistical difference was found (P<0.05) for each spinal region when
contrasting Days 30 and 0. A Wilcoxon Signed Ranks test with listwise exclusion was performed to determine if there were differences among the mean ranks (means) of the CSA mean symmetry score of the multifidus muscle of each participant. The grouping provided 4 values (T15–T16, T16–T17, T18–L1 and L1–L2) for each participant (P = 5); thus 20 paired values for analysis (n = 20). No statistical difference was found
(P<0.05) when contrasting Days 30 and 0. Thus there was no change in m. multifidus CSA or CSA symmetry ratio without WBV treatment.
Fig 2: The ultrasound image is of the left and right m. multifidus at the level of the T15–T16 articular facet joints and is representative of the images collected for the study. The ultrasonographic landmarks (dorsal spinous process, articular processes, mammillary process and lateral fascial border) can be seen between the m. multifidus and m. erector spinae.
(cm2) of the left and right m. multifidus. The SEM for the measuring of the CSA via imaging processing software (ImageJ)4 only ranged from 0.009 to 0.042. Complete validation information is available in Supplementary Item 1. The symmetry ratio of the m. multifidus CSA was
calculated according to the linear response formula of Reeves et al. (2006).
Ratio ¼
right m:multifidusCSA left m:multifidusCSA
If ratio1;symmetry ¼ ratio1
If ratio\1;symmetry¼ ratio 100%
fg100% 1
M. multifidus CSA with WBV For all analyses of m. multifidus CSA, data were grouped by spinal region. The grouping provided two values (left and right) for each participant (n = 9) at each spinal region; thus, a potential for 18 paired values for analysis (n = 18) at each spinal region. The n is provided for each analysis and those that are different than 18 are the result of missing data. The data are three repeated measures (Days 0, 30 and
60) and not normally distributed; thus a Freidman test with listwise exclusion was performed to determine if there were differences in mean ranks (means) of m. multifidus CSA at Days 0, 30 and 60 of WBV at each spinal region. A statistical
difference was found at spinal region T15–T16 (X2 (2, n = 16) = 22.88, (P<0.01); T16–T17 (X2 (2, n = 8) = 16.00, (P<0.01); T18– L1 (X2 (2, n = 16) = 30.13, (P<0.01) and L1–L2 (X2 (2, n = 8) = 13.00, (P<0.01). This indicates that there was a difference
among the three mean ranks (means) at Days 0, 30 and 60 at each of the spinal regions. The three orthogonal contrasts were performed using a Wilcoxon signed rank test with listwise exclusion. To hold the experiment wise type 1 error to less than 0.05, Bonferroni correction (comparison-wise alpha = 0.01) was used. The contrast between Days 0 and 30 at T15–
Statistical analysis All data analysis was completed using IBM SPSS Statistics for Macintosh Version 22.0.5 Unless otherwise stated, the alpha level of 0.05 (a = 0.05) used for inferential statistical and all tests were 2-tailed.
Results
Mean and standard deviation (s.d.) for all m. multifidus CSA measurements are available in Supplementary Item 2. One horse (B3) was sold and as such lost for the Day 60 m. multifidus CSA assessment follow-up. Due to poorer image quality in some horses (A1, A2, A3 and A4) related to the thickness of the skin and fat, not all borders of the m. multifidus were easily identifiable on ultrasound images at some levels (T16–T17 and L1–L2) and as such were not further analysed in those four horses.
M. multifidus CSA stability prior to WBV
The stability assessment data (Days 30 and 0) are repeated measures and not normally distributed; thus, a Wilcoxon
T16 (n = 18, z = 3.201, (P<0.01, r = 0.75), T16–T17 (n = 10, z = 2.803, (P<0.01, r = 0.89), T18–L1 (n = 18, z = 3.724, (P<0.01, r = 0.88); and L1–L2 (n = 10, z = 2.497, (P<0.01, r = 0.79) were found to be statistically significant at each spinal region. The contrast between Days 30 and 60 at T15–
T16 (n = 16, z = 3.154, (P<0.01, r = 0.79), T16–T17 (n = 8, z = 2.521, P<0.01, r = 0.89), T18–L1 (n = 16, z = 3.464, (P<0.01, r = 0.87); and L1–L2 (n = 8, z = 2.521, (P<0.01, r = 0.89) were found to be statistically significant at each spinal region. The contrast between Days 0 and 60 at T15–T16
(n = 16, z = 3.516, (P<0.01, r = 0.88) T16–T17 (n = 8, z = 2.521, (P<0.01, r = 0.89) T18–L1 (n = 16, z = 3.516, (P<0.01, r = 0.88) and L1–L2 (n = 8, z = 2.521, (P<0.01, r = 0.89) were found to be statistically significant at each spinal region. Additionally, the r effect size for each is greater than the absolute value of 0.75. Although there is minimal to
no information regarding effect size in the literature in this field, the r effect size is considered much larger than typical in many other fields (Cohen 1988; Nakagawa and Cuthill 2007); thus the authors feel this is a clinically relevant increase in m. multifidus CSA. In all cases, the statistically significant contrasts indicated that as the duration of WBV increased the
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