People spend almost a third of their life sleeping and understanding how the spine can adapt to a mattress is essential for promoting people's health. The general objective of this study is to study and evaluate the adaptation of the spine to a mattress. The primary objective is the assessment of the variation in the lumbar lordosis angle (sagittal plane) in the supine position, on a mattress, compared to the value measured in the supine position on a rigid surface.

Inclusion Criteria:

• Aged between 18 and 45 years old
• Female or Male sex
• Cognitive integrity
• Absence of usual contraindications to MRI

Exclusion Criteria:

• Clinical condition diagnosed by a doctor
• Spinal pathologies
• Pregnant woman
• Claustrophobia

Healthy people between 18 and 45 years of age.