Muscle activation patterns in subjects with and without low back pain.

OBJECTIVE

To analyze muscle activation patterns during various footplate perturbations, used as proprioceptive challenges in patients with low back pain (LBP) and in controls.

DESIGN

A prospective and controlled comparative study.

SETTING

Outpatient clinic.

PARTICIPANTS

Twenty subjects with chronic LBP and 20 age- and sex-matched controls.

INTERVENTIONS: The subjects underwent 5 sets of footplate perturbations in 3 directions with 16 perturbations for each set.

MAIN OUTCOME MEASURES: Latency, frequency, and asymmetry of muscle activation of the erector spinae, rectus abdominus, anterior tibialis, and gastrocnemius muscles were measured bilaterally with surface electromyography.

RESULTS

In the toes-up movements, subjects with LBP were significantly less likely to activate their rectus abdominus muscles (P=.02), and they were more likely to exhibit asymmetric muscle activation in the smaller forward movements (odds ratio=4.1, P=.03). The latter result appears to be driven by asymmetric contraction of the erector spinae and rectus abdominus.

CONCLUSIONS

Significantly more subjects with LBP than control subjects exhibited absent firing of trunk muscles during 2 of the 5 footplate perturbations. These results suggest an abnormality of the neuromuscular loop and may represent altered proprioception.