by Dennis Zacharkow, PT
It is important to analyze why people have a tendency to assume a slumped, kyphotic, sitting posture with prolonged sitting at a desk or table.
Bancroft (1913) referred to the tendency for the shoulders to be drawn forward in all work situations where the hands and arms are used in front of the body, such as with desk work. In addition, the forward inclination of the head that will occur at a horizontal desk in order to improve one's visual angle, will also have a tendency to throw the body out of erect balance, and into a slumped posture.
The excessive energy expenditure required to balance the trunk in a erect posture without proper back support will also favor a slumped, kyphotic sitting posture (Staffel, 1884; Coe, 1979).
Branton's work (1966) with strain gauges showed that the individual's center of gravity tends to drift slowly forward in a slumped, kyphotic anterior sitting posture. This would relate to Fahrner's comment (1865) that the trunk will drop forward by a series of jerks until its weight is supported by the forearms or elbows on the desk.
In addition to the above factors predisposing the individual to assume a slumped sitting posture, one of the most important to consider is the relationship of the chair to the desk. This relationship is frequently ignored, and it is often taken for granted that a forward-leaning posture is the only postural alternative for all desk activities.
Critical factors to consider in the chair-desk relationship are the height of the desk, the inclination to the desk and the horizontal distance from the edge of the desk to the seat (Hartwell, 1895; Scudder, 1892; Shaw, 1902; Bennett, 1928; Karvonen et al., 1962). The sitter will be forced to seek support from the desk and assume a slumped, forward-leaning posture for one or several of the following reasons:
A proper chair-desk relationship will enable the sitter to obtain proper sacral support and lower thoracic support with a slightly reclined posture of 5 degrees to 10 degrees (The YogaBack Posture).
A slightly reclined school sitting posture with an erect trunk was advocated by Lorenz (1888), Schenk (1894), and Schwatt (1910). Bennett (1928) referred to a slightly reclined sitting posture with proper back support as a position of "alert readiness."
Schuldt (1988) reported that it is possible to keep the static muscular load of the neck, shoulders, and upper thoracic spine at a low level in a sitting work posture with the trunk reclined slightly backwards and the cervical spine vertical. This posture gives lower neck, shoulder, and upper thoracic spine muscle activity levels than a sitting work posture with the entire spine straight and vertical, which in turn gives lower muscle activity levels than a sitting posture with the entire spine flexed forward.
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