This study aimed to investigate the spatial distribution and redistribution of lumbar erector spinae (ES) activity during a lumbar extension endurance task in pain‐free participants and how this is modified in people with low back pain (LBP). High density surface electromyography (HDEMG) was recorded using 13 × 5 electrode grids placed over the lumbar ES in 13 LBP and 13 control participants while completing an Ito test to task failure. The root mean square of the HDEMG signals was computed, a topographical map of the EMG amplitude generated and the centre of the activity (centroid) determined throughout the task. The centroid of the EMG amplitude map was systematically more cranial (F = 6.09, P = 0.022) for the LBP participants compared with the control subjects. Regression analysis showed that the extent of redistribution of ES activity was associated with longer endurance. These results show that LBP participants utilised a different motor strategy to perform the endurance task, characterised by greater activation of more cranial regions of the ES and less redistribution of ES activity throughout the task. This study provides new insight into the functional activation of the lumbar ES and how it is modified when people have pain.

The purpose of this study was to investigate differences in passive muscular stiffness between the superficial multifidus (SM) and deep multifidus (DM), and to compare their passive and active stiffness in individuals with low back pain (LBP) and asymptomatic individuals. Fifteen LBP individuals and 15 asymptomatic individuals were recruited. Passive stiffness of the SM and DM was measured bilaterally using sheer wave elastography (SWE) with participants lying prone. Active stiffness was measured for the SM during trunk extension, and the contraction ratio was calculated. DM displayed higher passive muscular stiffness than SM in both the asymptomatic and LBP groups (14.41±2.62 and 15.40±2.77 kPa respectively; t=7.765 and t=3.864, p<0.05). Individuals with LBP exhibited higher passive muscular stiffness of SM (LBP: 10.15±4.21, asymptomatic: 6.84±1.69 kPa; t=3.002, p<0.05) and a lower contraction ratio (LBP: 1.54±0.47, asymptomatic: 2.65±1.36kPa; p<0.05) compared to the asymptomatic group. The findings support a differentiation in passive muscular stiffness between SM and DM and provide evidence for an alteration in muscular stiffness at rest in individuals with LBP. The lower increase of muscular stiffness with contraction observed for those with LBP may reflect a deficit in activation of the multifidus.

No abstract

Recent research using high-density electromyography (HDEMG) has provided a more precise understanding of the behaviour of the paraspinal muscles in people with low back pain (LBP); but so far, HDEMG has not been used to investigate the flexion relaxation phenomenon (FRP). To evaluate this, HDEMG signals were detected with grids of electrodes (13 × 5) placed bilaterally over the lumbar paraspinal muscles in individuals with and without LBP as they performed repetitions of full trunk flexion. The root mean square of the HDEMG signals was computed to generate the average normalized amplitude; and the spatial FRP onset was determined and expressed as percentage of trunk flexion. Smoothing spline analysis of variance models and the contrast cycle difference approach using the Bayesian interpretation were used to determine statistical inference. All pain-free controls and 64.3% of the individuals with LBP exhibited the FRP. Individuals with LBP and the FRP exhibited a delay of its onset compared to pain-free controls (significant mean difference of 13.3% of trunk flexion).  They also showed reduced normalized amplitude compared to those without the FRP, but still greater than pain-free controls (significant mean difference of 27.4% and 11.6% respectively). This study provides novel insights into changes in lumbar muscle behavior in individuals with LBP.

No abstract