Test-retest reliability of laser displacement mechanomyography in paraspinal muscles while in lumbar extension or flexion

This study investigated test-retest reliability of mechanomyography (MMG) on lumbar paraspinal muscles. Healthy male and female subjects (mean ± standard deviation, 25 ± 9.4 years, BMI 21.8 ± 2.99, n = 34) were recruited. Two test sessions (one week apart) consisted of MMG (laser displacement sensor (LDS)) muscle evaluations over the 10 lumbar facet joints, and 2 bilateral sacral sites, in anatomical extension and flexion. Two-way repeated measures ANOVA with Tukey's post hoc showed no significant differences between testing sessions for the same position (p > 0.05). The intra-class correlation coefficients (ICCs) in extension were classified as 'very good' (0.8-0.9) for maximal muscle displacement (Dmax), contraction time (Tc) and velocity of contraction (Vr). Half relaxation time (½Tr) and half relaxation velocity (½Vr) were 'poor' (0.4-0.5) and 'good' (0.7-0.8). In flexion, Dmax, Tc and Vr were 'excellent' (≥0.9) whilst ½Tr and ½Vr were 'fair' (0.6-0.7) and 'very good'. Comparing extension against flexion, significant (p < 0.05) differences in Dmax and ½Vr were found (L1/L2-L5/S1). Tc was significant (p < 0.05) for all sites whilst Vc was for L1/L2 on both sides (p < 0.05). ½Tr showed no significance (p > 0.05). Most MMG-derived parameters thus appear as reliable measures of muscle contractile properties in lumbar extension and flexion, with flexion providing more reliable results (ICCs).