Novel mapping of the spatial distribution of lumbar muscle activity showed that individuals with low back pain lack a redistribution of activity during repetitive lifting.
This study investigated change in the distribution of lumbar erector spinae muscle activity and pressure pain sensitivity across the low back in individuals with low back pain (LBP) and healthy controls. Surface electromyographic (EMG) signals were recorded from multiple locations over the lumbar erector spinae muscle with a 13 × 5 grid of electrodes from 19 people with chronic nonspecific LBP and 17 control subjects as they performed a repetitive lifting task. The EMG root mean square (RMS) was computed for each location of the grid to form a map of the EMG amplitude distribution. Pressure pain thresholds (PPT) were recorded before and after the lifting task over a similar area of the back. For the control subjects, the EMG RMS progressively increased more in the caudal region of the lumbar erector spinae during the repetitive task, resulting in a shift in the distribution of muscle activity. In contrast, the distribution of muscle activity remained unaltered in the LBP group despite an overall increase in EMG amplitude. PPT was lower in the LBP group after completion of the repetitive task compared to baseline (average across all locations: pre: 268.0 ± 165.9 kPa; post: 242.0 ± 166.7 kPa), whereas no change in PPT over time was observed for the control group (320.1 ± 162.1 kPa; post: 322.0 ± 179.5 kPa). The results demonstrate that LBP alters the normal adaptation of lumbar erector spinae muscle activity to exercise, which occurs in the presence of exercise-induced hyperalgesia. Reduced variability of muscle activity may have important implications for the provocation and recurrence of LBP due to repetitive tasks.
aPain Clinic, Center for Anesthesiology, Emergency and Intensive Care Medicine, University Hospital Göttingen, Göttingen, Germany
bDepartment of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology (BFNT) Göttingen, Bernstein Center for Computational Neuroscience, University Medical Center Göttingen, Georg-August University, Göttingen, Germany
* Corresponding author at: Pain Clinic, Center for Anesthesiology, Emergency and Intensive Care Medicine, University Hospital Göttingen, Robert-Koch-Str. 40, Göttingen 37075, Germany. Tel.: +49 0 551 3920109; fax: +49 0 551 3920110.
Received 12 September 2013
Received in revised form 23 January 2014
Accepted 28 January 2014
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.