The effect of a unilateral sacroiliac joint manipulation on muscle activity and force output in the posterior oblique sling muscles

Abstract

Objective: The effects of spinal manipulation have been well documented, however, current literature poses a gap regarding the neurophysiological mechanisms responsible for these effects. Further evidence is required in order to uncover the specific neurophysiological mechanisms of spinal manipulative therapy (SMT) and its effect on muscle activity. The study aimed to investigate the immediate effect of a unilateral sacroiliac joint (SIJ) manipulation compared to a control on muscle activity (EMG in mV) and maximum voluntary force output (dynamometer in kg) in the posterior oblique sling (POS) muscles in asymptomatic participants. Methods: A randomised, controlled, pre-test, post-test design allowed for 34 participants, aged 18-45 years old, with joint dysfunction at the SIJ to be allocated to either a manipulation or a control group. Force output and muscle activity of the gluteus maximus (GM) and latissimus dorsi (LD) muscles were measured before and after the intervention. IBM SPSS was used to analyse the data with significance set at (p=0.05). Independent samples t-tests were used to determine significance within, and between, the groups, and Pearson correlation analysis looked for correlations between the muscles in the two slings. Results: There were no significant differences observed between the control and intervention groups for age (p=0.355), gender (p=0.688), race (p=0.338), BMI (p=0.142), and the side of joint fixation (p=0.473). The intra-group analysis and intergroup analysis showed no significant differences for peak amplitude and mean muscle activity of the muscles of the POS when assessed for intra- or intergroup comparisons. A significant difference between pre and post maximum force output in the right GM for both groups (intervention: p=0.016; control: p=0.030), and in the right LD for the control group only (p=0.032), was noted. However, there was no significant difference between group results for any muscle in terms of force output when assessed for intergroup comparisons. Conclusion: The results of this study showed no treatment effect of SIJ manipulation on the muscles of the POS in asymptomatic participants. Consideration should be given to the way SMT is administered, the type of sham intervention used and the protocol followed to elicit maximum voluntary isometric contraction (MVIC).