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_max/M_max 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_max/M_max 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_max/M_max ratios at the 10-second postlumbosacral procedure time point was greatest after the HVLA SM procedure. The effects of lumbosacral procedures on H_max/M_max ratios were similar between patients with subacute LBP and asymptomatic participants.

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

Author keywords: Low Back Pain, Mechanical, Lumbar Manipulation, H-Reflex, Gastrocnemius Muscle

Author affiliations:  JDD: Clinical Neurosciences Institute, Palmer College of Chiropractic Florida, Port Orange, Florida; JRB, PD: Research Department, New York Chiropractic College, Seneca Falls, New Yor

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