Differences in Feedforward Trunk Muscle Activity in Subgroups of Patients With Mechanical Low Back Pain

Abstract 

Silfies SP, Mehta R, Smith SS, Karduna AR. Differences in feedforward trunk muscle activity in subgroups of patients with mechanical low back pain.

Objective

To investigate alterations in trunk muscle timing patterns in subgroups of patients with mechanical low back pain (MLBP). Our hypothesis was that subjects with MLBP would demonstrate delayed muscle onset and have fewer muscles functioning in a feedforward manner than the control group. We further hypothesized that we would find differences between subgroups of our patients with MLBP, grouped according to diagnosis (segmental instability and noninstability).

Design

Case-control.

Setting

Laboratory.

Participants

Forty-three patients with chronic MLBP (25 instability, 18 noninstability) and 39 asymptomatic controls.

Interventions

Not applicable.

Main Outcome Measures

Surface electromyography was used to measure onset time of 10 trunk muscles during a self-perturbation task. Trunk muscle onset latency relative to the anterior deltoid was calculated and the number of muscles functioning in feedforward determined.

Results

Activation timing patterns (P<.01; η=.50; 1-β=.99) and number of muscles functioning in feedforward (P=.02; η=.30; 1-β=.83) were statistically different between patients with MLBP and controls. The control group activated the external oblique, lumbar multifidus, and erector spinae muscles in a feedforward manner. The heterogeneous MLBP group did not activate the trunk musculature in feedforward, but responded with significantly delayed activations. MLBP subgroups demonstrated significantly different timing patterns. The noninstability MLBP subgroup activated trunk extensors in a feedforward manner, similar to the control group, but significantly earlier than the instability subgroup.

Conclusions

Lack of feedforward activation of selected trunk musculature in patients with MLBP may result in a period of inefficient muscular stabilization. Activation timing was more impaired in the instability than the noninstability MLBP subgroup. Training specifically for recruitment timing may be an important component of the rehabilitation program.

Key Words: Electromyography, Low back pain, Motor skills, Reaction time, Rehabilitation

List of Abbreviations: COM, center of mass, Cont, contralateral to side of arm perturbation, DDD, degenerative disk disease, EMG, electromyography, EO, external oblique, ES, erector spinae, ICC, intraclass correlation coefficient, IO, internal oblique, IO/TrA, internal oblique/transversus abdominis, Isp, ipsilateral to side of arm perturbation, LBP, low back pain, LM, lumbar multifidus, MLBP, mechanical low back pain, MRI, magnetic resonance imaging, RA, rectus abdominis, RMQ, Roland-Morris Questionnaire, SF-36, Medical Outcomes Study 36-Item Short-Form Health Survey, v1, TrA, transversus abdominis