This study takes a look at patterns of trunk muscle contraction during sitting. They compare the results for healthy people with no back pain (control group) to adults with chronic low back pain (CLBP). Sitting upright and slumped sitting are both included.
EMG activity of 10 trunk muscles was recorded for both sitting on an unsupported stool and slumped or slouched sitting. Skin electrodes were used to measure abdominal and low back muscles.
Patients with CLBP showed no difference in muscle activity in the two postures. The healthy controls showed a clear difference in muscle activity between the two positions. The authors suggest the difference is a relaxation response seen normally in the slumped posture.
When the researchers divided the CLBP group into subgroups based on pattern of symptoms, there was a difference. Patients with pain during flexion had less muscle activity during usual sitting compared to the control group. It may be that the lack of muscular activity causes mechanical stress on the spine resulting in pain.
On the other hand, patients with pain during extension movements had hyperactive back muscles when sitting upright. They also did not relax during the slumped position.
The authors conclude that abnormal postural patterns in patients with CLBP can provoke strain and pain. Subgrouping or classifying patients helped bring this to light. CLBP patients who report increased pain during sitting should be classified as a flexion or extension pattern. A specific rehab approach can be used to improve or normalize muscular control and relaxation.