Objective: In a non-experimental, case-control study the abdominal muscles activities during abdominal hollowing exercise in supine and four points kneeling position were investigated in males suffering from non-specific chronic low back pain compare with healthy volunteers.

Materials & Methods : Twenty males suffering from non-specific chronic low back pain (mean age 39.9 years) and twenty healthy subjects (mean age 37.8 years, male) performed abdominal hollowing exercise in supine and four point kneeling position. The randomized task order were carried out three times in each position with one minute rest between attempts. Thickens of the right abdominal muscle was measured using a 7.5 MHz linear ultrasonography probe in both positions at end of quiet inspiration and mean of three measures was recorded. Changes of abdominal muscle thickness were expressed in percentage of muscle resting thickness. Transverse abdominus activity was isolated from activity of internal oblique muscle.

Results: There was significantly less increase of transversus abdominus thickness in patients compare with healthy group across both positions. Ratio of internal oblique thickness compare with transversus abdominus was significantly lower in healthy group. Changes of transversus abdominus thickness in supine position were significantly greater in patients, although changes of internal oblique thickness and its ratio were significantly greater in four point kneeling position.

Conclusion: It is difficult for non-specific chronic low back pain patients to isolate contraction of transversus abdominus from internal oblique muscle during abdominal hollowing exercise in four point kneeling position in comparison with supine position.