Sitting on an Office Chair and Bending Forward

When sitting on an office chair and bending forward, the pressure on the lumbar spine increases significantly, potentially leading to issues such as lumbar disc herniation and muscle imbalance.

Sharp Increase in Lumbar Pressure

When the chair is too low, causing the knees to be higher than the hips, the pelvis tilts backward, forcing a change in the natural lordotic curve of the lumbar spine. At this point, the anterior edge of the intervertebral disc is compressed, while the posterior edge is continuously stretched. The internal stress within the intervertebral disc in a flexed state increases sharply with the angle. When sitting for long periods with the body leaning forward, the pressure on the lumbar spine can soar to over 180 kilograms, equivalent to carrying a heavy person on your back while working. Maintaining this posture for extended periods deprives the lumbar intervertebral discs of rest, causing the nucleus pulposus to gradually be pushed backward. If the core muscle strength is weak and the lumbar spine lacks support, the annulus fibrosus is prone to rupture, ultimately leading to lumbar disc herniation.

Increased Load on the Posterior Lumbar Structures

Bending forward while sitting engages the muscles, ligaments, and joint capsules around the spine in silent weight-bearing. When the weight of the upper body remains constant, the moment arm increases due to the forward tilt of the trunk, amplifying the tension borne by the posterior lumbar structures. Each vertebra has to share an additional load. This continuous extra load accelerates degenerative changes in the lumbar spine and increases the risk of lumbar diseases.

Muscle Imbalance

To maintain stability, the body shortens the iliopsoas muscles to lock the hip joints and reduces the activity of the gluteal muscles to maintain a reclined sitting position, leading to muscle imbalance. This muscle imbalance not only affects the body's normal motor function but may also cause pain and discomfort.

Preventive Measures

To avoid these hazards, it is recommended to adjust the height of the office chair and desk so that the knees are naturally bent and do not exceed the height of the hips, with both feet flat on the ground. Keep the lower back naturally straight, with the back against the chair back, and the center of the screen at eye level. If the chair lacks lumbar support, place a cushion or lumbar pad to fill the gap behind the lower back, providing additional support and comfort.