The kneeling or Balaans chair is a brilliant solution to support the pelvis for forward work, and the position is relatively stable. The upper leg is fixed at the knee by a pad, and the pelvis is perched forward by a strong forward tilt of the pan.
The design of the kneeling chair is very effective to locate the pelvis in a stable position for forward tasks.
Unfortunately, there are trades in mobility to accomplish a stable forward posture. The legs are relatively fixed at the lower leg and hip, meaning that there is more pressure at the knee, less freedom of movement compared to a more conventional chair, and less support. There are no armrests on the chair, and reclined postures are not supported. Moving the chair, and getting in and out of the kneeling chair is not quite as easy as a conventional chair. Another difference is that kneeling in good posture requires a taller work surface for the desired forearm support when compared to a neutral seated posture, meaning a taller work surface may be needed.
Gym Balls and Ball Chairs
The Swiss ball, or gym ball can be very effective for exercise! The legs and torso encourage good spinal posture against the challenge of movement and gravity.
The exercise ball may not work so well in the long term as furniture because the height and location of the ball are not easily changed, and support at the low back and arms is not available.
There are variations on the gym ball to allow office work. A pad can be placed in a conventional chair (Sessile pad, Fit-sit) that mimics the freedom of movement a ball provides. A Ball chair is another design that uses casters under a frame around the ball that allows side-side movement at the desk, and the frame may have support for more low back stability.
Stools and Such
Seating can be designed to move. Some stools have up-down, front-back and side-side movement available. When the stool is positioned at a good height for the strength of the legs, neutral spinal postures are easier, particularly if a lot of body movement is needed. Unfortunately, the increased freedom to move means the chair has very little stability or support for more relaxed postures, but the legs get some relief from standing.
A tall stool is sometimes used at a work surface fixed for standing postures. A tall stool will not allow the feet on the floor, and because leg support is an important component of forward sitting, good forward postures are more difficult. The foot-ring or footrest may not allow the leg strength in the positions needed for the work. Another problem with tall seating is the limited pan tilt adjustment for forward work. The seat pans are usually tipped back for reclined postures, and forward work may cause slumped postures.
Several versions of saddle chairs allow a more open thigh-torso angle, and more movement in a sit-stand posture. Much like the moving stool, more freedom means less support. This design often has more sitting pressure between the legs than other designs.