Motor Neuron Excitability Attenuation as a Sequel to Lumbosacral Manipulation in Subacute Low Back Pain Patients and Asymptomatic Adults: A Cross-Sectional H-Reflex Study.

Objective: The purpose of the study was to compare a time series of tibial nerve H-reflex trials between patients with subacute low back pain (LBP) and asymptomatic adults using pre and post high-velocity, low-amplitude (HVLA) spinal manipulation (SM) and control procedures.

Methods: Asymptomatic adults (n = 66) and patients with subacute LBP (n = 45) were randomized into 3 lumbosacral procedures: side-posture positioning, joint preloading with no thrust, and HVLA SM. A time series of 40 H/M ratios at a rate of 0.1 Hz were recorded in blocks of 10 trials at baseline and after the lumbosacral procedures at time points corresponding to immediately after, 5 minutes after, and 10 minutes after the procedure. Descriptive time series analysis techniques included time plots, outlier detection, and autocorrelation functions. A mixed analysis of variance model (group × procedure × time) was used to compare the effects of lumbosacral procedures on H/M ratios between the patients with subacute LBP and asymptomatic participants.

Results: The time series analysis and the significant lumbosacral × time interaction term (P < .05) indicated that inhibition of the H/M ratios at the 10-second postlumbosacral procedure time point was greatest after the HVLA SM procedure. The effects of lumbosacral procedures on H/M ratios were similar between patients with subacute LBP and asymptomatic participants.

Conclusions: Although nonspecific effects of movement or position artifacts on the H/M ratio were present, a reliable and valid attenuation of the H/M ratio occurred as a specific aspect of HVLA SM in both asymptomatic adults and patients with subacute LBP.