Does Electromyographic Trunk Muscle Response to a Sudden Lower Limb Perturbations Differ with Chronic LBP

Abstract

PURPOSE: The topic of chronic low back pain (CLBP) has spawned vast research to aid understanding of the condition. Several authors have shown CLBP subjects demonstrate different trunk muscle recruitment, compared to asymptomatic individuals during both upper and lower limb movements. Research has yet to evaluate trunk muscle onset in response to a sudden unexpected lower limb perturbation in subjects with or without a history of CLBP. This study attempted to determine if a difference in muscle onset occurs between these groups. METHODS: Nine male participants with a history of CLBP (22.5 ± 5.2 yrs) and nine matched asymptomatic controls (21.7 ± 3.2 yrs). All subjects were exposed to three sudden lower limb perturbations. Throughout each trial onset of trunk muscle activity of Transversus Abdominis (TvA), Obliquus Internus (OI),Obliquus Externus (OE), Rectus Abdominis (RA) and Multifidus (MU) was measured using surface electromyography (sEMG) with onset determined via a computer derived algorithm. Ethical approval for testing was obtained from the ethics committee of St Mary's College (Twickenham). RESULTS: In healthy subjects a sudden lower limb perturbation resulted in sEMG activation ofTrA/OI (−18 ± 8 ms); OE (−20 ± 2ms) andRA (−17 ± 8ms) in advance of activity of the prime mover (Peroneus Longus (PL)), activity of MU occurred (9 ± 21 ms) after the prime mover. Similar trunk muscle activity was noted in subjects with CLBP with onset of TrA/OI (−24 ± 4 ms), OE (−26 ± 5 ms) and RA (−15 ± 6 ms) in advance of the prime mover and MU (28 ± 7 ms) active after the prime mover. CONCLUSIONS: Control subject data adds to the growing evidence highlighting activity of trunk muscles in a feed-forward manner prior to limb movement. In subjects with a history of CLBP no significant differences (P>0.05) in onset of muscle activity were found compared to control subjects, in stark contrast to experimental evidence that suggests CLBP subjects present with altered trunk muscle onset during limb perturbations. Methodological factors may explain these findings such as insufficient statistical power and large temporal variability between trials and subjects. Further research using a larger subject cohort and more stringent CLBP classification criteria into sub groups may minimize the variability within the methods.