Changes in Pressure Pain Thresholds and Basal Electromyographic Activity After Instrument-Assisted Spinal Manipulative Therapy in Asymptomatic Participants: A Randomized, Controlled Trial

ObjectiveThe purpose of this study was to investigate the effects of instrument-assisted spinal manipulative therapy (SMT) targeted to the low-back region on changes in pressure pain thresholds (PPTs) and basal electromyographic activity (BEA) in asymptomatic participants.MethodsA repeated-measures, single-blind, randomized trial was conducted on 30 participants, 19 men and 11 women (mean age, 24.5 ± 3.9 years), without a current history of low-back pain. Each participant attended all 2 treatment group sessions and received instrument-assisted SMT or a sham manipulation procedure. Instrument-assisted SMT was administered using the Activator Method protocol. Bilateral PPT levels over L5-S1 zygapophyseal joints, L5 dermatome, and first dorsal interossei in the hand and bilateral BEA of low back and neck region were assessed pre- and posttreatment by an assessor blinded to the treatment allocation of the participant. A 3-way analysis of variance with time (pre-post) and side (ipslateral, contralateral to the intervention) as within-group variable and intervention (manipulation or sham) as between-group variable was used to evaluate changes in PPT. A paired sample t test was used to analyze the differences between pre- and posttreatment in BEA.ResultsThe group vs time interaction was statistically significant for PPT irrespective of the site tested or the side treated. Participants receiving the instrument-assisted SMT experienced greater improvement in PPT when compared with the control group. Paired sample t tests for BEA only show an immediate decrease in BEA of the paraspinal muscle on the pelvic deficiency side of the low-back region.ConclusionsThe application of instrument-assisted SMT resulted in an immediate and widespread hypoalgesic effect with local muscle relaxation in asymptomatic participants. It is hypothesized that therapeutic mechanisms, either segmental or central, may be involved in the therapeutic effects of instrument-assisted SMT.