Young Blonde Girl With The Old Chair And The Mirror

Some chairs have two curved bands of wood (also known as rockers) attached to the bottom of the legs. They are called rocking chairs.
A kneeling chair adds an additional body part, the knees, to support the weight of the body. A sit-stand chair distributes most of the weight of the occupant to the feet. Many chairs are padded or have cushions. Padding can be on the seat of the chair only, on the seat and back, or also on any arm rests and/or foot rest the chair may have. Padding will not shift the weight to different parts of the body (unless the chair is so soft that the shape is altered). However, padding does distribute the weight by increasing the area of contact between the chair and the body. A hard wood chair feels hard because the contact point between the occupant and the chair is small. The same body weight over a smaller area means greater pressure on that area. Spreading the area reduces the pressure at any given point. In lieu of padding, flexible materials, such as wicker, may be used instead with similar effects of distributing the weight. Since most of the body weight is supported in the back of the seat, padding there should be firmer than the front of the seat which only has the weight of the legs to support. Chairs that have padding that is the same density front and back will feel soft in the back area and hard to the underside of the knees.
There may be cases where padding is not desirable. For example, in chairs that are intended primarily for outdoor use. Where padding is not desirable, contouring may be used instead. A contoured seat pan attempts to distribute weight without padding. By matching the shape of the occupant's buttocks, weight is distributed and maximum pressure is reduced.
Actual chair dimensions are determined by measurements of the human body or anthropometric measurements. The two most relevant anthropometric measurement for chair design is the popliteal height and buttock popliteal length.