Several mechanisms have been theorized for the mechanical and neurophysiological basis of SMT, including stimulation or modulation of the somatosensory system to evoke neuromuscular reflexes . Forceful stretching of the spinal muscles induces relaxation after SMT. Other mechanisms are induced hypoalgesia , kinematic correction [34, 35] and increased lumbar range of motion . A brief reduction in intradiscal pressure during SMT in cadavers and return to baseline within less than 1 min was reported in one earlier study . Another study showed reduced H-reflex amplitude in patients with unilateral disc herniation, which improved after SMT . The improved outcomes in our patients can be attributed to two main factors. Firstly, SIJ manipulation may improve normal functioning of the lumbar spine and related muscles . Secondly, lumbar side-posture rotational manipulation can induce spinal muscle relaxation , improve lumbar range of motion , and briefly decrease intradiscal pressure .