Apparently it has been proven that a rocking motion has a therapeutic effect on humans. When rocking your blood pressure falls and respiration slows. The physical act of rocking taps into a pleasure centre located in the brain somewhere between the one for chocolate and the one for music.

Also the human spinal cord cannot function in both directions at the same time. When an occupant of the rocking chair uses his legs to rock the chair, the impulses required to move the legs are coming down from the brain through the spinal cord. This does not leave scope for the pain impluses to travel up to the brain through the spinal cord, thus resulting in pain relief in the back area.
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