Mechanical force spinal manipulation increases trunk muscle strength assessed by electromyography: A comparative clinical trial

Objective: The objective of this study was to determine whether mechanical force, manually-assisted (MFMA) spinal manipulative therapy (SMT) affects p araspinal muscle strength as assessed through use of surface electromyograp hy (sEMG). Design: Prospective clinical trial comparing sEMG output in 1 active treatm ent group and 2 control groups. Setting: Outpatient chiropractic clinic, Phoenix, AZ. Subjects: Forty subjects with low back pain (LBP) participated in the study . Twenty patients with LBP (9 females and 11 males with a mean age of 35 ye ars and 51 years, respectively) and 20 age- and sex-matched sham-SMT/contro l LBP subjects (10 females and 10 males with a mean age of 40 years and 52 years, respectively) were assessed. Methods: Twenty consecutive patients with LBP (SMT treatment group) perform ed maximum voluntary contraction (MVC) isometric trunk extensions while lyi ng prone on a treatment table. Surface, linear-enveloped sEMG was recorded from the erector spinae musculature at L3 and L5 during a trunk extension p rocedure. Patients were then assessed through use of the Activator Methods Chiropractic Technique protocol, during which time they were treated throug h use of MFMA SMT. The MFMA SMT treatment was followed by a dynamic stiffne ss and algometry assessment, after which a second or post-MVC isometric tru nk extension and sEMG assessment were performed. Another 20 consecutive sub jects with LBP were assigned to one of two other groups, a sham-SMT group a nd a control group. The sham-SMT group underwent the same experimental prot ocol with the exception that the subjects received a sham-MFMA SMT and dyna mic stiffness assessment. The control group subjects received no SMT treatm ent, stiffness assessment, or algometry assessment intervention. Within-gro up analysis of MVC sEMG output (pre-SMT vs post-SMT sEMG output) and across -group analysis of MVC sEMG output ratio (post-SMT sEMG/pre-SMT sEMG output ) during MVC was performed through use of a paired observations t test (POT T) and a robust analysis of variance (RANOVA), respectively. Main Outcome Pleasures: Surface, linear-enveloped EMG recordings during iso metric MVC trunk extension were used as the primary outcome measure. Results: Nineteen of the 20 patients in the SMT treatment group showed a po sitive increase in sEMG output during MVC (range, -9.7% to 66.8%) after the active MFMA SMT treatment and stiffness assessment. The SMT treatment grou p showed a significant (POTT, P < .001) increase in erector spinae muscle s EMG output (21% increase in comparison with pre-SMT levels) during MVC isom etric trunk extension trials. There were no significant changes in pre-SMT vs post-SMT MVC sEMG out put for the sham-SMT (5.8% increase) and control ( 3.9% increase) groups. Moreover, the sEMG output ratio of che SMT treatment group was significantly greater (robust analysis of variance, P = .05) tha n either that of the sham-SMT group or that of the control group. Conclusions: The results of this preliminary clinical trial demonstrated th at MFMA SMT results in a significant increase in sEMG erector spinae isomet ric MVC muscle output. These findings indicate that altered muscle function may be a potential short-term therapeutic effect of MFMA SMT, and they for m a basis for a randomized, controlled clinical trial to further investigat e acute and long-term changes in low back function.