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.