|Best Way to Sit: Tilt the Seat Forward (Sitting Postures)|
Balanced sitting posture on forward sloping seat
by A.C.Mandal.MD. Copenhagen
Our industrialized society is transforming into an information processing society in which more employees are transacting business while sitting for long periods of time.
For the last century, work chairs in schools, factories and offices have been designed for sitting upright, with the hip, knees and ankles all at right angles. Until recently, it was widely believed that people sat with a 90-degree bending of the hip joint while preserving lordosis (concavity) of the back.
The erect posture looks very nice, but it is impossible to sit this way for long and there is no scientific basis for it. It is entirely based on wishful thinking, morals and discipline from the days of Queen Victoria. This erect sitting posture cannot be maintained for more than one or two minutes, and usually results in fatigue, discomfort and poor posture.
In 1962, the German orthopedic surgeon, Hanns Schoberth, demonstrated by x-ray photos that in a seated work position, you can only bend about 60 degrees in the hip-joints, not 90 degrees as shown in the drawings in fig.1. This means that when moving from a standing (lordosis) to an upright sitting position, you bend the hip-joints about 60 degrees and rotate the pelvis axis backwards, flattening the lumbar-curve (kyphosis) of the back 30 degrees and straining the muscles of the back. (fig.2) When leaning forward over the desk, you have to bend another 40-50 degrees, and this bending mainly takes place in the 4th and 5th lumbar discs. Even the best lumbar support will hardly have any influence on the posture when leaning over the desk.
J.J.Keegan, an American Orthopedic surgeon, made in 1953 a series of x-rays of people lying on their sides which documented the large movements that took place in the lumbar section of the spinal column as the position changed from standing (a) to right angle sitting (c) and bent-over positions (d).(b) is the natural resting position, as when you lie on your side while sleeping. The lumbar curve is retained and the muscles are relaxed and well-balanced.(fig.3)
A sitting posture that approaches the natural resting position (b), is a more suitable position and allows the spine to carry the body weight in a more comfortable way. This is "Balanced Seating".
A seat that tilts forward encourages this natural posture. Opposing muscle groups are balanced and the lumbar curve is preserved producing balanced seating in which the back is straight, the joint angles are open and the muscles are relaxed. This position provides greater mobility and relieves pressure on the lungs and stomach.
To further evaluate the effect a forward tilting seat has on the flexion, forward bending, of the back, I conducted an experiment to document the results. To record the changes in the flexion of the various parts of the body, the anatomical points were marked at the knee-joints, hip-joints, 4th lumbar disc and shoulder joints. The participant was seated at a fixed height for the seat and work surface, but the feet were placed incrementally in three different positions in order to simulate different work heights, and the seat and work surface were tilted. To begin with, the girl was positioned at the conventional right angle (Fig.6), whereupon the chair seat and work surface were tilted incrementally and the position of the feet lowered to simulate an increase in the chair and work surface heights (Fig.7 & 8). Fifty photographs of each of 3 positions were taken during a period of 10 days to record the changes in the flexion.
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