Table 5 Estimated marginal means (95% CI) for muscle volume (mm3), relative volume (mm3) and muscle fat infiltrate (expressed as a percentage of muscle volume) for each muscle from linear mixed models adjusted by side (left /right), muscle, spinal level, gender, age, and BMI, with Bonferroni-adjusted mean differences between groups
 Characteristic | Groups |  | Difference between groups |  |
|---|---|---|---|---|
|  | Pain(n = 47) | Asymp*(n = 35) | Pain minus Asymp | P |
Volume | ||||
 Levator scapulae | 867.9 (835.5 to 900.2) | 908.6 (870.5 to 946.8) | -40.8 (-90.6 to 9.1) | 0.108 |
 Multifidus (with semispinalis cervicis) | 1352.5 (1320.0 to 1385.1) | 1275.7 (1237.3 to 1314.2) | 76.8 (26.6 to 127.0) | 0.003 |
 Semispinalis capitis | 591.9 (559.6 to 624.2) | 553.1 (515.0 to 591.2) | 38.8 (-11.1 to 88.6) | 0.126 |
 Splenius capitis with splenius cervicis | 678.5 (646.2 to 710.8) | 700.6 (662.5 to 738.7) | -22.1 (-72.0 to 27.7) | 0.381 |
  Longus colli | 241.1 (208.8 to 273.4) | 217.6 (179.5 to 255.7) | 23.5 (-26.3 to 73.4) | 0.351 |
 Sternocleidomastoid | 1075.5 (1043.2 to 1107.8) | 1058.5 (1020.3 to 1096.6) | 17.0 (-32.8 to 66.9) | 0.500 |
Relative volume | ||||
 Levator scapulae | 769.18 (737.9 to 800.5) | 809.44 (772.6 to 846.3) | -40.3 (-88.5 to 8.0) | 0.101 |
 Multifidus (with semispinalis cervicis) | 986.51 (955.0 to 1018.0) | 969.11 (932.0 to 1006.2) | 17.4 (-31.1 to 65.9) | 0.478 |
 Semispinalis capitis | 497.8 (466.5 to 529.1) | 470.18 (433.3 to 507.1) | 27.6 (-20.6 to 75.9) | 0.258 |
 Splenius capitis with splenius cervicis | 588.14 (556.9 to 619.4) | 618.3 (581.4 to 655.2) | -30.2 (-78.4 to 18.1) | 0.217 |
 Longus colli | 198.9 (167.6 to 230.2) | 178.8 (141.9 to 215.7) | 20.0 (-28.2 to 68.3) | 0.411 |
 Sternocleidomastoid | 932.7 (901.5 to 964.0) | 916.0 (879.1 to 952.9) | 16.7 (-31.5 to 65.0) | 0.492 |
Muscle fat infiltrate | ||||
 Levator scapulae | 11.6 (10.2 to 13.0) | 11.9 (10.3 to 13.6) | -0.3 (-2.4 to 1.8) | 0.769 |
 Multifidus (with semispinalis cervicis) | 26.9 (25.5 to 28.3) | 24.6 (22.9 to 26.2) | 2.3 (0.2 to 4.5) | 0.034 |
 Semispinalis capitis | 15.6 (14.2 to 17.0) | 15.0 (13.3 to 16.6) | 0.6 (-1.5 to 2.8) | 0.547 |
 Splenius capitis with splenius cervicis | 13.7 (12.3 to 15.1) | 12.8 (11.1 to 14.4) | 0.9 (-1.2 to 3.1) | 0.392 |
 Longus colli | 17.9 (16.5 to 19.3) | 17.2 (15.6 to 18.9) | 0.7 (-1.5 to 2.8) | 0.545 |
 Sternocleidomastoid | 14.2 (12.8 to 15.5) | 15.0 (13.4 to 16.7) | -0.9 (-3.0 to 1.3) | 0.418 |