Low back pain (LBP) is the leading cause of disability worldwide since 1990. Its chronic form (lasting longer than 3 months) affects 10 to 15% of cases and represents 70 to 90% of the total cost of low back pain. Most LBP is classified as non-specific because the pain’s source cannot be precisely established in 85%–90% of cases. The need to identify subgroups of nonspecific chronic low back pain (NSCLBP) was highlighted by both clinicians and researchers in order to optimize therapeutic management. In this context, a project of NSCLBP subgroup identification based on a multifactorial approach has been established. Indeed, several factors contribute to the development and the persistence of NSCLBP. Alterations in the activity of the lumbar muscles have been suggested as one of these contributing factors. This doctoral work has focused on these alterations and represent a part of the subgroup identification project.Literature reported various alterations in the lumbar muscles activity of the NSCLBP patients during several tasks. Among these alterations, neuromuscular asymmetry between the left and right side was reported to influence muscle recruitment, rehabilitation and persistence of pain. These elements make neuromuscular asymmetry an important factor in understanding the pathophysiology of NSCLBP. However, few studies have investigated right / left asymmetry of lumbar muscle activity during functional tasks of the daily life. Studying this asymmetry would allow a better understanding of the pathophysiology of NSCLBP.This doctoral work aimed to characterise the neuromuscular asymmetry of NSCLBP patients in comparison with asymptomatic participants. To achieve this objective, several complementary studies were successively conducted.As a whole, this doctoral work highlights a global alteration of the activity of the lumbar muscles in NSCLBP patients during the four motor tasks studied. Most of these alterations aimed to enhance the stability of the spine but lead to potential long-term consequences. Neuromuscular asymmetry is one of these alterations but seems to be present only during maximal trunk forward bending. Considering the clustering project is mainly based on the alterations observed in the NSCLBP population, the integration of the asymmetry of the flexion-relaxation phenomenon may represent an interesting parameter in the process of identification of the subgroups. It would also be useful to extend the analysis to the abdominal and pelvis muscles as well as to evaluate the influence of the psychological parameters for a deeper understanding of these results.