Comparison of upper trapezius muscle stiffness between female assembly workers with and without myofascial trigger points

BackgroundMuscle stiffness in the upper trapezius (UT) muscle is a significant parameter for evaluating myofascial trigger points (MTrPs). Because the measuring position influences UT muscle stiffness, investigating UT muscle stiffness in different working postures would be useful for evaluating and planning effective interventions for MTrPs.ObjectiveTo identify differences in UT muscle stiffness measured in the resting and working postures among female assembly workers, both with and without MTrPs.MethodsEighteen female workers with right (Rt) side UT MTrPs and 18 workers without MTrPs participated in this study. We measured UT muscle stiffness on both sides in resting and working postures using MyotonPRO. A multivariate analysis of variance was used to investigate the differences in UT muscle stiffness.ResultsIn the working posture, the MTrPs group exhibited a significantly higher UT muscle stiffness on the Rt side, measuring 386.22 N/m, compared to the non-MTrPs group (335.22 N/m, <i>p</i> = 0.007). No significant difference was noted between the groups in the resting posture. However, the MTrPs group demonstrated greater difference in stiffness (working-resting posture) (DSWR) on the Rt side of the UT muscle (MTrPs, 62.61 N/m; non-MTrPs, 31.56 N/m; <i>p</i> = 0.019).ConclusionClinicians should consider measuring muscle stiffness in the working posture and DSWR.