Abstract: A seat assembly can be mounted on various wheelchair bases. The seat assembly enables the seat width and backrest width to be adjusted independently of each other. A backrest has a plurality of open slots, the number and orientation of which contributes to depth, width, and height adjustment of the backrest as well as angular adjustment of lateral supports to permit the backrest to conform to the anatomical curves of a user. A backrest foam assembly comprises multiple foam sections that are adapted to be positioned relative to each other and thereby vary the overall width of the assembly. A cover comprises multiple sections, each covering a foam section. A multi-position adjustable armrest assembly combines large-scale and small-scale adjustments, which provides a broad range of adjustment for the armrest and its position. A power recline mechanism with programmable shear reduction includes a dual rotary recline mechanism.