MANUFACTURERS REPS INC

Can I sit and stay healthy?
Salli-Saddle
Lots of studies have been made and published about how dangerous sitting is. The focus has been only on conventional 90/90 sitting (hips and knees in 90 degree angles) that really sets in motion many harmful processes. Below is a more comprehensive and accurate explanation of the problem. 
Dangerous sitting = conventional 90/90 sitting
The main health dangers come from decreased circulation of blood (4–6 l) and lymph which move in over 400.000 km of vessels, through all internal organs, including about 700 lymph nodes. The circulation is the main function of the body. Any long-term disturbance in it disturbs metabolism and reduces health.
The circulation in 90/90 sitting is disturbed because of
  1. the muscle tension in the back, neck and shoulders
  2. the pressure of the upper body on buttocks and thighs
  3. the pressure in the abdominal cavity due to the slouched posture
  4. the pressure and weakened circulation in the groin vessels and soft tissues, caused by tight clothes
  5. the 90 degree angles in the hips and knees that create pressure on the vessels in them
  6. the pressure of tight clothes that get even tighter in 90/90 sitting
  7. the shallow breathing caused by the slouched posture and muscle tensions
  8. poor physical activity; motion is the "engine” of circulation; the heart circulates only 25 % of the blood.
Healthy metabolism requires relaxed muscles and a certain amount of repeated movements (= changes of pressure in the soft tissues that keep the fluids moving). The conventional sitting limits movement efficiently. Relaxed muscles and changing position (= pressure areas) repeatedly, as happens during sleep, is enough for sufficient circulation and metabolism. In conventional sitting this does not happen due to tensions and the static pressure areas.
Problems of standing
Standing is not all good either. People who work standing know the problems of arthritis, poor circulation in legs and tired back and hips. Overall standing is quite strenuous and not suitable for everyone in the long run. Some serious efforts have been made to make standing a solution but they have more or less failed. Standing surely has its place, it is ok for few individuals, and for short breaks in various jobs, but it is definitely not the solution to end all sitting-related problems.
Alternative: healthy sitting
The healthiest option is to sit on a two-part saddle chair, in riding- like position (135/135 degree angles) in good posture and with the pelvis tilted forward, the same way as in standing. Further, the chair should be equipped with easily rolling castors and an active seat, the height of the table must be properly adjusted and clothes must not be too tight. This way the sitter has a good posture and deeper breathing, good circulation in all main vessels, no pressure on the joints in the lower extremities, and hardly any muscle tensions.
Saddle sitting produces valuable physical activity through
  1. sitting and swinging the seat intentionally, or unconsciously as it usually happens
  2. rolling and reaching (emphasize by placing things a bit further)
  3. getting up from the chair regularly, "walking and talking” (preferably with an ear plug and blue tooth) or standing; standing up from a saddle chair is easy and does not strain the joints in the same way as getting up from conventional chairs.
The most advanced activity method is to keep some simple exercise equipment close by and do short and light "circulation exercises” (4–6 times) during the day. One can also do push-ups or steps forward, etc. for activation.

The statements on the page are based on the following sources:
Michael Adams, Nikolai Bogduk, Kim Burton, Patricia Dolan: The Biomechanics of Back Pain
David A. Rubenstein, Wei Yin, Mary D. Frame: Biofluid Mechanics, an Introduction to Fluid Mechanics, Macrocirculation, and Microcirculation
Marcus J. Seibel, Simon P. Robins, John P. Bilezikian: Dynamics of Bone and Cartilage Metabolism, Principles and Clinical Applications