Quantitative intramuscular myoelectric activity of quadratus lumborum during a wide variety of tasks

Intramuscular fine-wire electrodes monitored the electromyographic activity of quadratus lumborum in four young adults. A wide variety of tasks were performed including flexion tasks, lateral bending, twisting, extension, and lifting tasks. Heavy lifts of barbell weights up to 70 kg activated the quadratus lumborum 74% of their maximum on average while surface recording of erector spinae (L3) were only 62% of their maximum activation. The quadratus lumborum was more active (54%) than other muscles during isometric side support postures where the body is held horizontally almost parallel to the floor as the subjects supported themselves on one elbow on the floor together with both feet. Furthermore, it increased activation in response to increasing compression in static upright standing postures.