by Dennis Zacharkow, PT
A kneeling chair is a unique design of a forward-sloping seat without a backrest. In order to keep the buttocks from sliding forward on the seat, the sitter's legs are supported just below the knees by a large padded support. As a result, the sitter's lower legs are tucked under the seat. This sitting posture results in a more open thigh-to-trunk angle than when using more conventional chairs, along with a greater degree of knee flexion.
Diffrient (1984) commented that the kneeling chair would most benefit those individuals who wanted to work in a forward-leaning posture over a desk. Among the disadvantages of this design, Diffrient mentioned that without a backrest one is unable to assume a backward-leaning posture and obtain back support. Therefore, the sitter is limited to forward-leaning and upright postures.
Diffrient (1984) also mentioned the potential problems of constant pressure on the shins, and the fact that the sitter's feet are in a cramped position. Thompson (1985) also referred to the potential problem with pressure on the knees, along with the awkward positioning of the toes.
The possibility of increased discomfort in the knees and lower legs suggested by Diffrient (1984) and Thompson (1985) was also noted in the comfort ratings of university students after two hours of sitting in a kneeling chair (Porter and Davis, 1983).
An extensive study by Drury and Francher (1985) involved the comfort ratings for a kneeling chair with a 15-degree forward slope to the seat. The kneeling chair was evaluated over a 2 1/2 hour session. Five one-half hour training periods were previously given to all the subjects in order to adjust to the kneeling chair.
The comfort ratings showed that the greatest discomfort with the kneeling chair involved the legs and knees, and to a lesser extent the back and buttocks. For some individuals, a major problem involved difficulty getting into and out of the kneeling chair.
According to Drury and Francher (1985):
"Despite the training given in use of this chair, the overall comfort was not particularly good. Results were worse in overall magnitude than the earlier prototype conventional chair tested, and discomfort increased with time-on-task rather than remaining level.
Body parts affected by the novel chair were primarily the legs, particularly knees and shins. Knee discomfort, presumably from the acute knee angle, was noticeable. For this increased leg discomfort there was little or no corresponding decrease in back discomfort. Although subjects had the theory of the chair explained to them during training and tried to sit with a lordotic spine, they often slumped forward to give a kyphotic curve instead."
Bridger (1988) found a common postural adaptation to the kneeling chair to be an "erect slumped" posture. In the "erect slumped" posture, "the trunk has tilted rearward about the hip joints, which have extended. The upper body is erect but the spine is flexed" (Bridger, 1988).
Another description for this "erect slumped" posture is a "postural depression," which refers to the hinging forward of the front of the rib cage towards the pelvis (Anderson, 1951; Zacharkow, 1998). (See Figure 1.)
The same "postural depression" occurs when leaning against the backrest of most chairs, and also when leaning forward improperly.
Proper support to the lower thoracic spine is the only way to correct this main postural fault of sitting: the "postural depression" or hinging forward of the front of the rib cage towards the pelvis (Zacharkow, 1988, 1998).
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