Spatial distribution of erector spinae activity in people with low back pain during a dynamic lifting task

Previous studies utilising high-density electromyography (HDEMG) have revealed subtle differences in the distribution of the superficial lumbar paraspinal muscle activity during both static and dynamic tasks in people with LBP. In the current study, we extend this work by uniquely evaluating the effect of chronic LBP on the spatial distribution of activity in both the thoracolumbar and lumbar erector spinae (ES) activity during a dynamic lifting task. Ethical approval was granted from the University of Birmingham. Eleven LBP (5 men; 32.5±16.3years) and fourteen control (CON) participants (6 men; 27.7±11.4years) completed this study. HDEMG was acquired from the ES using four 64-channel (13x8) semi-disposable HDEMG grids (two grids bilaterally) placed over the lumbar and thoracolumbar ES. The spatial distribution of muscle activity was quantified as the centre of activity in the cranio-caudal axis (centroid); and the homogeny of signals (entropy). Reflective kinematic surface markers were placed over the trunk to track spinal kinematics. The dynamic task involved lifting a 5kg weighted box between two anterior shelves at knee and sternum height. No differences in spinal kinematics were identified between groups (P>0.05) reflecting the standardised nature of the task. For both lifting and lowering movements, the distribution of ES activity was centred in a more cranial position (P<0.05). For the lifting phase, the mean LBP centroid was 82±5mm cranial to the base of the electrode grids whereas for the CON group the centroid was 78±8mm. For the lowering phase, the centroid was positioned 84±9mm in the cranial direction for the LBP group and 78±8mm for the CON. Additionally, LBP participants displayed a less even spatial distribution of ES activity throughout the task, reflected as systematically lower entropy (p