In cervical spine, under friction free circumstances a force of approximately 7 percent of the total body weight separates the vertebrae. A minimum force of 11.25 to 13.5KG (25 to 30 lb) is necessary to lift the weight of head when sitting and to counteract the resistance of muscle tension. The greatest amount of separation occurs during the first few minutes of treatment at a given force. To avoid treatment soreness, the first treatment should not exceed 10 to 15 lb. Muscle relaxation can be achieved at levels less than those needed for mechanical separation (4.5 to 6.75KG, or 10 to 15 lb) in the cervical spine. Progression of dosage at succeeding treatment will depend upon the goals and patient reactions
The references for above mentioned text are:

Therapeutic Exercises, Foundation and Techniques, 3rd Edition by Kisner & Colby

Mobilization of Spine by G.P.Grieve, Fifth Edition

So they are quite authentic references and no doubt about them


Junior Physio as you said,
total wight of head is =(20-25)Kg.
As usually we apply athird to half of that wieght which is(8-12)Kg.
as wieght of body'll stabilize her body .
Is it the weight of head or the weight of a trunk or lower limb. I guess that you are wrong in that case because the total weight of the head is not as that large. The weight of the head is 7% of the total body weight for average individual with normal body weights usually. That figures don't apply to the individuals who are very much over weight. So if an individual has a body weight of 70KG, his head weight will be 4.9Kg or 10.78 lb (pounds). So the spinal traction for pain relieving purposes will be 4.9Kg or 10.78 lb (pounds).

A minimum force of 11.25 to 13.5KG (25 to 30 l) is necessary to lift the weight of head when sitting and to counteract the resistance of muscle tension.
Actually these figures of traction in the cervical region are used for mechanical separation of the vertebrae as used in reducing the dislocations of subluxations of vertebrae in the spinal region.