Low back pain (LBP) is the leading cause of disability worldwide. Impaired postural control is a key factor in the development and maintenance of LBP. Moreover, the prevalence of LBP is associated with impairments in diaphragm function, symptoms of dyspnea, and dysfunctional breathing. However, the association between LBP (and more specifically postural control) and hyperventilation remains unknown. The main objective of this project is to investigate whether the presence of recurrent non-specific LBP is related to the presence of hyperventilation, when classified either objectively by decreased carbon dioxide values (demonstrating hypocapnia) or by symptoms while showing normal carbon dioxide values. Moreover, the investigators will explore whether psychosocial factors play a role in this relation. Subsequently, the investigators will examine whether hyperventilation in LBP patients is related to impaired postural control, and more specifically to a decreased postural contribution of the diaphragm.