Purpose: Non-specific chronic low back pain (NSCLBP) patients present with reduced back extensor muscle endurance which could be explained by the higher fatigability of their lumbar muscles. However, studies investigating lumbar muscle fatigability have shown contradictory findings. Furthermore, none investigated potential asymmetry in lumbar muscle fatigability, despite neuromuscular asymmetry being reported as a risk factor for NSCLBP. The present study's primary purpose was to determine whether NSCLBP patients presented with higher lumbar muscle fatigability and fatigability asymmetry than asymptomatic participants.
Methods: Thirty NSCLBP patients and 23 asymptomatic participants performed the Sorensen test. The median frequencies from the electromyographs of the right and left erector spinae longissimus (ESL) and lumbar multifidus (LMF) were measured during the test. A linear regression was performed on the median frequencies on each muscle. Slope and initial median frequency were extracted to characterize fatigability. Asymmetry was quantified by the absolute differences between right-side and left-side muscle pairs.
Results: NSCLBP patients presented significantly poorer back extensor muscle endurance than asymptomatic participants. No differences were found between NSCLBP patients and asymptomatic participants in terms of fatigability or fatigability asymmetry for either the ESL or LMF. The initial median frequency in both muscles was significantly lower among NSCLBP patients.
Conclusions: The present study showed that NSCLBP patients did not present higher fatigability or higher fatigability asymmetry in lumbar muscles than asymptomatic participants. The heterogeneity of the NSCLBP population, due to the absence of any specific etiology, may explain these findings. These slides can be retrieved under Electronic Supplementary Material.
Keywords: Back extensor muscles endurance; Electromyography; Muscle fatigability; Neuromuscular asymmetry; Non-specific chronic low back pain.