Relaxed Posture of Cerebral Palsy Children

An ergonomic study of their relaxation chair

Abstract

As one of the studies of human posture, the author noticed abnormal muscle tones of cerebral palsy children and measurements were conducted on levels of acceleration of muscle tones in the relaxed posture. Ten types of chairs with different seat tilts and back rest inclinations were chosen and changes in muscle contraction were mentioned electromyographically. Nine subjects all severely involved cerebral palsy children.
Angle of each type of chair is as follows: A type: Seat at an angle of 10 degrees to the horizontal line and back rest at a level of 5 degrees from vertical line to the front. B type: Seat at an angle of 15 degrees to the horizontal line and back rest at a level of 10 degrees from vertical line to the back. C type: Seat at an angle of 10 degrees to the horizontal line and back rest at level of 10 degrees from vertical line to the back. D type: Seat at an angle of 5 degrees to the horizontal line and back rest at a level of 10 degrees from vertical line to the back. E type: Seat is same degree with horizontal line and back rest at a level of 10 degrees from vertical line to the back. F type: Seat at an angle of 15 degrees to the horizontal line and back rest at level of 20 degrees from vertical line to the back. G type: Seat at an angle of 10 degrees to the horizontal line and back rest at a level of 20 degrees from vertical line to the back. H type: Seat is same degree with horizontal line and back rest at a level of 20 degrees from vertical line to the back. I type: Seat at an angle of 10 degrees to the horizontal line and back rest at a level of 30 degrees from vertical line to the back. J type: Seat at an angle of 10 degrees to the horizontal line and back rest at a level of 40 degrees from vertical line to the back.
As a general tendency of the relationship between EMG level and the ten types of chairs, it was found that EMG decreased as the angle of the relaxation chair increased.
The effects on the EMG level of three factors such as type of chair, sample muscles, and subject were tested by the analysis of variance. The results were as follows:
Factor of type of chair: F=3.984(f₁=8, f₂=64), factor of muscle: F=10.723(f₁=5, f₂=40), and factor of subject: F=21.38 (f₁=8, f₂=320). These values were significant at the 1% level. The EMG level was compared between the above 10 types of chairs and the sum of the EMG levels of different muscles in percentages to that of A type was B type 64%, for C type 50%, for D type 62%, for E type 60%, for F type 42%, for G type 30%, for H type 32%, and for I type 42%. The EMG level in case of G and H types was decreased to about Two- Thirds of that of A.
As for the interaction on the EMG level of the three factors of the variance ratio was computed at 1.38(f₁=40, f₂=320) in the case of chair and subject, at 6.566 (f₁=40, f₂ =320) in the case of those of muscle and subjects.
The level of the latter two cases were significant at the 1% level. However, the interaction of the factors of chair and muscles was not significant. This shows the effect of chair on the EMG level independent from the kind of muscle tested.
Therefore, it can be concluded that the G type was the most adequate one among the 10 types of chair tested from the view point of suppressing involuntary muscular contraction of the patient.