This study will test the within and between day variability of spinal kinematics and trunk muscle activity in healthy subjects and chronic low back pain patients during various daily-life activities.

This study will test the within and between day variability of spinal kinematics and trunk muscle activity in healthy subjects and chronic low back pain patients during various daily-life activities. Participants will come twice to the motion laboratory. During the first session, participants will first perform different functional activities (V1), such as sit-to-stand, gait, lifting tasks, stepping up. Their spinal kinematics will be measured with a camera-based system (VICON) using a multi-segment spinal model and trunk muscles activity will be recorded with surface electromyography. After a break, participants will have to perform all the functional activities a second time (V2). These two measures (V1 and V2) will be used to determine the within day variability of spinal kinematics. Finally, all participants will come one week later (V3) to repeat all the measurements to determine the between day variability.

Inclusion Criteria:

• sufficient French level to understand the instructions for the tests, the information sheet, the consent form and the questionnaires
• All chronic low back pain patients should present with non-specific low back pain (pain from lower ribs to gluteal folds) for more than 3 months.

Exclusion Criteria:

• pregnancy
• body mass index (BMI) that is above 32
• patients should not have any sign of specific low back pain such as the presence of infection, rheumatological or neurological diseases, spinal fractures, any known important spinal deformities, previous back surgery that limits spinal mobility, tumours
• high level of pain at the time of experiment that prevents repeated movements (severity and irritability)
• other concomitant pain or condition that could compromise the evaluation of spinal kinematics.

Chronic low back pain patients