the ergonomics behind Backtyping

In professional literature, there are discussions regarding the correct sitting position in front of the computer, the height of the keyboard, support for the forearms and head positioning. The ergonomic keyboard's advantages, in that respect, are great. While typing, the ergonomic keyboard relieves pressure from the lower back, relaxes the shoulders, relieves pressure from the root of the palm muscles, and prevents unwanted movements of the root of the palm. The keyboard allows the user to change positions while working.

1. While typing on a regular keyboard, the hand positioning should be forward. This position enhances the pressure on the lumbar spine (as the hands are positioned more forward, the frontal moment grows, increasing pressure of the lower back) and on the shoulder muscles. In the ergonomic keyboard, the hands are positioned closer to the body, reducing the lumbar spine's movement and reducing pressure on the shoulder muscles. (The illustration bellow depicts different sitting positions and their affect on the spinal pressure).
2. Many studies indicate that the recommended back tilt in a sitting position is approximately 110-120 degrees. This angle enables a frontal turn of the pelvic and prevents the straitening of the back, increasing the pressure on the vertebras of the lower back. In addition, by leaning back, some of the body weight is supported, relieving pressure from the lower back. While using a regular keyboard, this position of tilting the back backwards, does not always allow comfortable typing. In order to reach the mouse and keyboard, the person typing needs to lean forward. In the agronomic keyboard, the keyboard is close to the person typing and there is no need to lean forward.    
3. A common problem in computer users is "Tennis Elbow": changes to the extensor tendons of the root of the arm, located in the elbow. The changes are caused by ongoing strain on the root of the arm mussels that help maintain the hand aligned statically over the mouse and keyboard. In that case, even placing the elbows on a hand rest will not relieve the pressure on the muscles. The agronomic keyboard does not have use of these muscles since the hand is placed in mid-position, a position considered in the literature as the preferred position for the root of the hand, with relatively little strain.
4. Extending and bending motions of the root of the palm wrist which increase the risk for "Carpel Tunnel Syndrome"- a thickening of the tendons in the palm canal which results in a pressure of the tendons on a nerve, which causes a disruption of sensations in the fingers and sometimes in all muscles. In the ergonomic keyboard the root of the palm is stationary without extending or bending motions.
5. The ergonomic keyboard decreases arm deviations in sideways motions. These movements cause a host of other problems.
6. Another advantage of the ergonomic keyboard: It allows for the changing of positions to a bigger variety of movements, It allows typing while standing or while sitting on a couch, all that without the restrictions of a regular keyboard. Changing positions in prolonged usage of the computer is also recommended in professional literature.