Evaluation of trunk muscle activity in chronic low back pain patients and healthy individuals during holding loads.

OBJECTIVES: Low back pain after load-carrying is the most important disorder in musculoskeletal system and a cause of dysfunction and economic problems. Holding materials can disturb spinal stability; nevertheless, there are few researches about the pattern of trunk muscle recruitment in patients with chronic low back pain (CLBP) during load holding.
METHODS: Ten female patients with CLBP and ten matched healthy subjects participated in this study. Normalized electromyography activation of trunk muscles during holding loads was analyzed.
RESULTS: The low back pain group demonstrated significantly higher activation levels of the External oblique abdominis muscle during loading 12 kg in flexed trunk position and lower activation levels of the Internal oblique abdominis muscle during loading 6 and 12 kg in neutral trunk position than the control group. With the highest external load and trunk flexion, the electrical activity of back muscles increased significantly in both groups. With increasing load, the activation of Rectus abdominis muscle in patients with CLBP and the activation of Rectus abdominis and Internal oblique muscles were increased significantly in healthy subjects.
CONCLUSION: Higher activation of global and lower activation of local abdominal muscles in patients with CLBP may represent that pain changes neuromuscular control systems. The increased activity of extensor muscles during trunk flexion is probably needed for stability and controlling of flexion.