The Benefits of Reclined Posture
Forget What Your Mother Said About "Sitting Up Straight"
Research has shown that while sitting, the position of the pelvis determines the shape of the spine (Schoberth, 1970). In a seated position, the pelvis shifts backward causing the spine to flatten or curve outward (Anderson, 1979). Like most postural distortion patterns of the spine, the key lies with the position of the pelvis as it is foundational to the spine’s posture. With a forward slumping spinal posture, the pelvis is excessively posteriorly tilted compared to its anatomic position.
As a person moves from an upright posture to a reclined posture, the pelvis rotates forward, resulting in a larger lumber curvature.When the lumbar moves, movement also occurs in the upper back. This movement helps eliminate stress and pain on the upper back. Research has shown for quite some time that reclining postures pump nutrients into the intervertebral discs (Anderson 1981) and reduce the load on the lumbar spine and paraspinal musculature (Anderson, 1974) through the transfer of upper body weight to the chair. This can be a significant effect, reducing forces on the lower back by as much as 20 percent.
In 2006, Scottish and Canadian researchers used a form of magnetic resonance imaging (MRI) to better understand the strain sitting puts on your back. Their findings show that best position in which to sit at your desk is reclined, at about 135 degrees, not upright like our mothers told to us to sit!
In the MRI study, respondents assumed three different postures: a forward leaning slumped posture, an upright 90-degree posture and reclined position of 135-degrees. Spinal disk movement occurs when weight-bearing strain is placed on the spine, causing the internal disk material to misalign. Disk movement was found to be most pronounced with a 90-degree upright sitting posture.
“The 90-degree posture results are counter to what most people consider most healthy,” said Waseem Amir Bashir, M.B.Ch.B, clinical fellow in the Department of Radiology and Diagnostic Imaging at the University Alberta Hospital, Canada.
It was the least pronounced at a 135-degree posture, suggesting that less strain is placed on the spinal disks and associated muscles and tendons in a reclined posture. The forward “slouch” position revealed a reduction in spinal disk height, signifying a high rate of wear and tear on the lowest spinal levels. As a result, Dr. Bashir and colleagues advise patients to stave off future back problems by correcting their sitting posture and finding a total ergonomic environment that allows the optimal reclined position of 135 degrees.
What's the Best Recline Angle?
While a 135 degree recline is the best sitting position for backs, it's important understand the effects of this deep recline to the neck.With the back in deep recline, the head must move forward to allow adjustment for visual lines. Without the support of a headrest, reclined angles of 110-115 degrees are optimal to minimize forward head posture. It's important in reclined postures to ensure that the entire back be positioned against the backrest to take advantage of the support available.
Beyond the scientific anatomical advantages of recline, observational research has shown that when the constraint of desktop technology is removed, the vast majority of people prefer to sit in a semi-reclined or reclined posture, similar to those assumed while driving a vehicle, chatting during casual conversations or sitting on a favorite chair at home.
The History of the Ergonomic Chair
Chair tilting mechanisms have been around for a long time and provide users with the ability to assume reclined postures.
The Centripetal Spring Chair or Armchair was a 19th-century American office chair, and one of the first modern designs for office chairs. Designed in 1849 by the American inventor Thomas E. Warren, the Spring Chair allowed tilt movement in all directions, and was achieved through the flexion of the four large C-shaped steel springs on which the seat rested, using the sitter’s feet as a fulcrum.
Today’s ergonomic work chairs have come a long way since the Centripetal Spring Chair. Highly sophisticated chairs such as Herman Miller's Aeron chair are designed with technologically advanced tilt mechanisms which follow the body’s pivot points at the ankle, knee and hip during recline. Work surfaces, desks and height adjustable tables, on the other hand, are fully fixed into place and are therefore unable to follow the kinematic recline of the much more sophisticated ergonomic chair.
The armchair as depicted in the 1851
Given that today’s desks are unable to synchronize with ergonomic chairs, users are most often constrained to static, upright or forward leaning postures. Reclined sitting postures are seldom sought except for an occasional stretch, phone call or reflective thought.This situation sets up a work environment that under utilizes the ergonomic chair’s performance, and more importantly, robs the user of healthful reclined postures.