PROBLEM TO BE SOLVED: To provide a chair with which a person can sit down for a long time without getting tired, raises the pelvis effortlessly and comfortably only by sitting, lets the lumbar spine, the thoracic vertebra, the cervical spine and the head into a line from the pelvis so that he/she can have deep abdominal respiration and get relaxed.SOLUTION: An accurate arc is made on a seating face in a lateral direction, a gentle convex surface is made on the whole seating face in an anteroposterior direction and a gentle projection is made at a position just in front of the ischium on the seating face, a backrest has a projection at a position 1 cm below the height of the iliac crest in the upper coxal bone and the backrest has a space avoiding contact with the spine. The positional relation between the front end of the backrest and the peak of the rear seating face is determined by the pelvis position and the size of lumbar curvature and the part touching the iliac crest of the backrest is formed with a projection. The last fine adjustment is made by using a seating comfortableness test tool based on the data measured in advance.
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