Temporal and spatial characteristics of post-silent period electromyographic bursting in low back muscles: comparison between persons with and without low back pain.

Purpose/aim: Recently, a novel measure of cortical disinhibition was identified using transcranial magnetic stimulation (TMS). This measure, described as post-silent period electromyographic (EMG) bursting, may inform on the corticomotor control of movement in health and disease; however, it has not been investigated for muscles outside the hand or in musculoskeletal conditions. Thus, the aim of this study was to investigate the temporal and spatial characteristics of "EMG bursting" in individuals with and without low back pain (LBP).

MATERIALS AND METHODS: TMS was used to map the motor cortical representation of paraspinal muscles in 11 individuals with LBP and 11 pain-free controls. The latency, duration and magnitude of bursting, number of active burst sites, map volume and coordinates of the burst "hotspot" were compared between the groups.

RESULTS: In pain-free controls, the latency, duration and magnitude of bursts were similar to the hand; however, bursts occurred earlier and were of smaller magnitude in LBP. Bursting was widespread throughout the cortical representation in both groups; however, there was a trend towards smaller mean EMG burst and map volume in LBP.

CONCLUSIONS: We confirm the presence of EMG bursting in back muscles and provide a description of the spatial profile of this mechanism. Our observations in LBP suggest that cortical disinhibition may be altered in this condition.