The aim of this study was to assess changes in deep abdominal muscle function after 8 weeks of exercise in chronic low back pain patients. Patients (n ¼ 109) were randomized to specific ultrasound guided, sling or general exercises. Contraction thickness ratio in transversus abdominis (TrA), obliquus internus (OI) and externus (OE), and TrA lateral slide were assessed during the abdominal drawing-in maneuver by b-mode ultrasound. Changes in abdominal muscle function were also regressed on changes in pain. Only modest effects in deep abdominal muscle function were observed, mainly due to reduced activation of OI (contraction thickness ratio: 1.42e1.22, p ¼ 0.01) and reduced TrA lateral slide (1.26e1.01 cm, p ¼ 0.02) in the ultrasound group on the left side. Reduced pain was associated with increased TrA and reduced OI contraction ratio (R2 ¼ 0.18). It is concluded that 6e8 treatments with specific or general exercises for chronic low back patients attained only marginal changes in contraction thickness and slide in deep abdominal muscles, and could only to a limited extent account for reductions in pain.

Keywords: Exercise, LBP, Abdominal muscles, Thickness