Spine. 2008 Mar 15;33(6):581-7. Sakai Y, Matsuyama Y, Nakamura H, Katayama Y, Imagama S, Ito Z, Okamoto A, Ishiguro N. STUDY DESIGN: A randomized controlled trial. OBJECTIVE: To investigate the effect of muscle relaxant for muscle blood flow at the trunk muscle in patients with chronic low back pain (LBP). SUMMARY OF BACKGROUND DATA: Paraspinal muscle function is widely believed to play a role and considered to be of etiologic significance in LBP, and intramuscular pressure increases and blood flow decreases in the flexion position. Decrease in oxygenated hemoglobin at the trunk muscle is seen in patients with LBP. METHODS: A total of 74 male patients with LBP lasting more than 6 months were randomized to 3 treatment groups: (1) physical therapy only (control) (n = 25), (2) administration of eperisone hydrochloride (EMPP) for 4 weeks (n = 24), and (3) McKenzie therapy (n = 25). The primary outcome variables, observed at 2 and 4 weeks, are the Japanese Orthopedic Association LBP score, visual analogue scale (VAS), Faces Pain Scale-Revised, and SF-36. Intramuscular oxygenation was evaluated using near-infrared spectroscopy during lumbar extension and flexion, and oxygenated hemoglobin and deoxygenated hemoglobin were compared. RESULTS: VAS was significantly lower at 4 weeks in the McKenzie group than in the control group. There were no significant changes at 2 weeks in all parameters, however, the relative change of oxygenated hemoglobin during lumbar extension at 4 weeks was significantly higher in the EMPP group when compared with the other 2 groups. The relative change of deoxygenated hemoglobin during lumbar flexion showed a significant difference at 4 weeks in the EMPP group when compared with the control group. CONCLUSION: Administration of EMPP for 4 weeks improved the LBP in VAS, though not as effective as McKenzie therapy. Our data demonstrated the effects of eperisone hydrochloride on paraspinal muscle hemodynamics improving intramuscular oxygenation during lumbar extension and flexion in patients with chronic LBP.