Lumbar erector spinae and sacral multifidus contractile properties in healthy females and males as determined by laser displacement mechanomyography

Introduction: To investigate mechanomyography's (MMG) applicability to characterise the contractile properties of muscles in the low back of healthy subjects. Methods: Healthy female and male subjects (mean ± standard deviation, 25.7 ± 9.6 years, BMI 21.8 ± 3.1 kg/m, n = 32) were studied with laser displacement mechanomyography (LDS MMG). The protocol consisted of MMG muscle evaluations over the 10 lumbar facet joints, as well as two bilateral sites over the sacrum, whilst subjects maintained lumbar flexion. Results: Mixed-effects model analyses with Sidak's post hoc were used for statistical analysis. Muscle contraction time (Tc), half-relaxation time (½Tr) and sustain time (Ts) showed no significant (p > 0.05) differences between segments or sides. No significance (p > 0.05) was found for muscle displacement (Dmax), contraction velocity (Vc) and ½ relaxation velocity (½Vr) between sides for the same vertebral segment. However, Dmax and Vc showed both left- and right-side differences (p 0.05). Conclusions: Contractile properties of the lumbosacral spine appear predominantly homogeneous, with no difference between sides (Tc, ½Tr, Ts). However, muscle displacement (Dmax) and contraction velocities (Vc, ½Vr) did vary between cephalic and caudal vertebral levels. This may be attributed to the difference in muscular CSA between the segments. As a preliminary analysis, gender appears to have no effect but requires future investigation