Study design: Experimental study.Background: Mechanical low back pain often presents with a non-optimal movement. If thehamstrings are relatively stiffer than the lumbar spine, which is relatively more flexible, it canlead to an increased load on the lumbar spine followed by pain. Muscular stiffness can bedefined as the passive resistance to elongation of the muscle. To this date it is not known towhat extent active (CNS controlled) or intrinsic passive factors contribute to muscularstiffness.Objectives: Investigate whether the stiffness in the hamstrings relative to stiffness in thelumbar spine in women is similar when they are awake and when they are sedated.Methods: Eleven healthy women planning to perform plastic surgery to the upper bodyunder anaesthesia were included. A passive straight leg raise was conducted before and rightafter sedation, and the degree of hip flexion when the lumbar spine started to move intoflexion was recorded.Results: The mean degree of hip flexion preoperatively was 54.45 ± 18.27° and 71,09 ±19,34° under anaesthesia. There was a significant difference between the measures (p=0.006).Conclusion: The results indicate that during sedation, the stiffness in the hamstrings is lowerthan when being awake. The difference might be explained by during anaesthesia themuscular system active response and the neural system control of reflex or activecontractions is lower since the passive factors within the muscle are unchanged.