Change in regional activity of the quadratus lumborum during bridge exercises

Context: The quadratus lumborum (QL) is expected to contribute to segmental motor control of the lumbar spine to prevent low back pain. It has different layers (anterior [QL-a] and posterior [QL-p] layers), whose functional differences are becoming apparent. However, the difference between the QL-a and QL-p activities during bridge exercises utilized in rehabilitation is unclear. Objective: To compare QL-a and QL-p activities during bridge exercises. Design: Repeated-measurement design was used to assess electromyographic activity of trunk muscles recorded during 14 types of bridge exercises. Setting: University laboratory. Participants: A total of 13 healthy men with no history of lumbar spine disorders participated. Intervention: The participants performed 14 types of bridge exercises (3, 3, and 8 types of side bridge, back bridge, and front bridge [FB], respectively). Main Outcome Measures: Fine-wire electromyography was used for QL-a and QL-p activity measurements during bridge exercises. Results: Both QL-a and QL-p showed the highest activity during the side bridge with hip abduction (47.3% [29.5%] and 43.0% [32.9%] maximal voluntary isometric contraction, respectively). The activity of the QL-a was significantly higher than that of the QL-p during back bridge with ipsilateral leg lift and FB elbow-toe with ipsilateral arm and contralateral leg lift (P < .05). With regard to the QL-p, the activity of the FB hand-knee with contralateral arm and ipsilateral leg lift, the FB elbow-knee with contralateral arm and ipsilateral leg lift, and the FB elbow-toe with contralateral arm and ipsilateral leg lift were significantly higher than that of the FB elbow-knee and FB elbow-toe (P < .05). Conclusion: This study indicates different regional activities; the QL-a activated during the back bridge with ipsilateral leg lift and FB with ipsilateral arm lift, and the QL-p activated during the FB with ipsilateral leg lift. These results have implications for the rehabilitation of low back pain or lumbar scoliosis patients based on QL recruitment.