Erector spinae muscle fibre size estimation using high-density surface electromyography in people with and without non-specific chronic low back pain: a cross-sectional study

There is limited evidence on whether lumbar erector spinae (ES) fibre morphology is altered in people with low back pain (LBP), due to the inherent challenges with biopsy studies. High-density surface electromyography (HDsEMG) provides an opportunity to assess motor unit properties, allowing non-invasive estimation of muscle fibre morphology. This cross-sectional study compares estimates of ES muscle fibre size and activity in people with and without non-specific chronic LBP and examines correlations with clinical features in those with LBP. HDsEMG data was acquired from the ES from people with and without non-specific chronic LBP (28/group) during isometric lumbar extension at maximum and submaximal levels (10%, 30%, 50%, 70%). HDsEMG signals were decomposed to estimate motor unit conduction velocity (MUCV), fibre diameter (FD), and fibre cross-sectional area (CSA). Additionally, global estimates from topographical HDsEMG amplitude maps were assessed including amplitude, entropy and y- and x- barycentre locations. There were no significant differences between the groups for MUCV ( p = 0.1310), FD ( p = 0.1310), or CSA ( p = 0.2875). Differences in the regional activation of ES along the y-axis ( p = 0.009) and entropy ( p = 0.023) were observed between groups. In conclusion, estimated ES fibre morphology did not differ between people with and without chronic LBP. However, an alteration of the spatial distribution of ES activity was observed for those with chronic LBP. These findings suggest that alterations in neuromuscular function may occur in individuals with non-specific chronic LBP in the absence of detectable differences in estimated ES muscle fibre size.