An adjustable resistance hinge system for a joint connecting at least a first articulating member and a second articulating member, the hinge system comprising a central element defining a hinge axis. The central element comprises a first and a second elongate arm, each elongate arm extending away from the hinge axis, and a first and a second keeping element hinging on the hinge axis are attached to the first and the second articulating members, respectively. A first and a second biasing device are also engageable with the first and the second elongate arms, respectively. The first and the second elongate arms extend into the first and the second articulating members, respectively, and the first and the second biasing devices engage the central element to resist relative motion of the first and the second articulating members about the hinge axis. The adjustable resistance hinge system allows two joined members to be adjusted to replicate desired physiology, limits, and resistance.

A joint for floor cleaning machines, comprising: a first portion, a second portion which is articulated to the first portion, a third portion which is articulated to the second portion; the joint comprises: first stable inclination element for the stable inclination of the second portion with respect to the first portion, second stable inclination element for the stable inclination of the third portion with respect to the second portion, the first stable inclination element and the second stable inclination element being connected to a single lever and being operable by the single lever.