The main objective of this study is to investigate the muscle metabolism in individuals with chronic non-specific low back pain (CNSLBP) to enhance our understanding of chronic back pain.

The NSCBP group:

• At least 6 patients will be included in this study.
• All patients referred to Vestfold Hospital Trust, Kysthospitalet, diagnosed with chronic NSCBP >3 months duration will be invited to participate in the study. The invitation will be in a written form.

Exclusion Criteria:

• anamnesis of medical or drug abuse,
• surgery on the musculoskeletal system of the trunk,
• known congenital malformation of the spine or scoliosis,
• body mass index > 27 kg/m2,
• systemic-neurological-degenerative disease,
• history of stroke,
• psychiatric disorder,
• pregnancy and abnormal blood pressure. The subjects will be asked not to use any medications except for paracetamol preparations one week before examination and instructed not to perform any back-straining exercise for 48 h prior to the study, except for ordinary daily working and/or leisure activities.

Persons referred to Hospital of rehabilitation due to chronic non-specific low back pain