Sitting—An Electromyographic and Mechanical Study

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Abstract
The study was based on materials of healthy subjects, patients with back pain but without roentgenographically demonstrable changes or back weakness, patients with back pain showing slight roentgenographic changes and disc degeneration, and patients with back pain having severe roentgenographic back changes and spondylosis deformans. The 1st group consisted of 40 healthy subjects (20 males and 20 females); and 2nd, 10 subjects, (3 males and 7 females); the 3rd, 10 subjects (8 males and 2 females); and the 4th, 10 subjects (7 males and 3 females). Individual groups 2-4 consisted of patients who sought advice of the Outpatient Department of Orthopedic Surgery because of back pain. A special chair was designed to study different sitting positions as well as the individual differences between such positions. The chair had an adjustable seat height and adjustable angle of the back, and a back pad which was adjustable in the vertical and the horizontal plane. With an angle of 100[degree] and 110[degree] between the seat and the back of the chair the electromyographic activity was recorded for the long extensors of the back, with and without the back pad screwed forwards from 1-3 cm, which produced a lordosis, and backwards 1-3 cm, with a corresponding degree of kyphosis. Two different chair designs were desirable, one with an angle of 110[degree] between the seat and the back of the chair for persons with a normally mobile spine and the 2nd chair with an angle of 100[degree] for persons with decreased mobility of the spinal column. In both cases, the back of the chair should be curved to fit a spine with 1- 2 cm of lordosis. The text is illustrated by line drawings, photographs, and the results presented in form of tables and graphs. Sixteen references are cited.

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