Investigation of the Putative Correlation Between Involuntary Psoas Activity During Passive Flexion of the Trunk at the Hips

Passive flexion of the trunk (relative to the legs) may be accompanied by contraction of the psoas muscles, even when the subject has been told not to contract any muscles. The psoas contraction is involuntary and cannot be controlled by the subject. This lack of passivity might be concomitant with lower back pain: the impairment may be present when lower back pain is present and/or absent when lower back pain is absent. The study's primary objective is thus to determine the sensitivity and/or specificity of a clinical test for impaired hip flexor passivity in cases of lower back pain during passive flexion of the trunk (from the supine position,). The secondary objective is to show that a negative test (after administration of correcting measures) is correlated with a decrease in pain (i.e. pain intensity and the functional repercussions of pain).