A chair assembly includes a seat support structure, a back support structure, a back tensioning assembly adjustable between low and high tension positions, an actuator assembly adapted to adjust the back tensioning assembly between the low and high tension positions, a control input assembly actuable by rotating the portion of the control input assembly, and a control link assembly operably coupling the control input assembly with the actuator assembly to adjust the back tensioning assembly between the low and high tension positions upon rotation of the portion of the control assembly by a seated user, wherein a number of rotations of the portion of the control input assembly is not limited by the control link.

A chair, comprising, a backrest, a seat coupled with the backrest, a column coupled with the seat, a linkage statically attached to the backrest and rotatably attached below the seat, a leaf spring statically attached at one end and in direct contact with the linkage to provide a resistance to tilting of the backrest relative to the column. A first structure fixed to the column, where a portion of the first structure has an arc shape that includes one or more teeth, and a second structure in contact with the first structure, wherein a portion of the second structure includes one or more teeth. The chair is configured such that, when a weight is applied to the seat, the one or more teeth of the second structure, a pivot point at which the backrest is configured to tilt relative to the column, and the linkage are configured to move together.

A chair, comprising, a backrest, a seat coupled with the backrest, a column coupled with the seat, a linkage statically attached to the backrest and rotatably attached below the seat, a leaf spring statically attached at one end and in direct contact with the linkage to provide a resistance to tilting of the backrest relative to the column. A first structure fixed to the column, where a portion of the first structure has an arc shape that includes one or more teeth, and a second structure in contact with the first structure, wherein a portion of the second structure includes one or more teeth. The chair is configured such that, when a weight is applied to the seat, the one or more teeth of the second structure, a pivot point at which the backrest is configured to tilt relative to the column, and the linkage are configured to move together.

A flexible support device for chair back tilting contains: a supporting frame, a seat mounting, and a base. The supporting frame includes a back portion, two peripheral extensions, two rotatable edges, two first coupling orifices, and two second coupling orifices. The seat mounting includes a first fixing portion, a second fixing portion, two connecting fences, two rotatable locating portions, two defining orifices, two joining elements, two slide orifices, and a drive protrusion. The base includes two locating fringes with two first positioning orifices, two second positioning orifices, a holder connected with a first end of a spring, and a second end of the spring is connected with a flexible sheet. The flexible sheet has two peripheral sections. The base further includes two connection segments, and the two connection segments have two openings. Two connectors are configured to accommodate the flexible sheet and have two pegs.

A chair that provides movement of a seat about an axis of rotation above the seat plane with the seat having a sensor in communication with a computer system that tracks movement. The seat may be simultaneously pivotable about a second axis of rotation defining a range of motion for the seat about the two axes. An actuation system in communication with the computer system can move the seat to desired positions and/or prevent the seat from being positioned at certain locations within the range of motion. The computer system may also include an application that can promote user movement within the seat and allow movement of the seat to be used for gaming, health monitoring and treatment, activity tracking, and the like. The chair may include a mechanism that has one or more glides operably received in curved structures to provide the movement about the axes.