Spring articulation structure

A spring articulation structure for play, fitness training and sports instruments, said spring articulation structure comprising a core element supported by and between two elastic springs in the form of two rubber rings, a shaft element fitted to said core element, and a shell compactly surrounding said core element and said rubber rings, said shell connected to a bottom plate, and having a top part defining an aperture having a downwardly narrowing conical surface for movably supporting the shaft element, wherein said elastic springs in the form of two rubber rings are configured and adapted to support said shaft element in a rest position, and to provide a free and flexible rocking motion in any direction to said core element and said shaft element by compressing when said shaft element is displaced in a first direction from said rest position, thereby providing a first force on said core element in a second direction, such that upon release of said shaft element, said first force provided by said two rubber rings accelerates said core element in said second direction, displacing said shaft element back to and beyond said rest position, compressing said rubber rings to produce a second force on said core element that slows, stops, and changes the motion of the shaft element, thereby causing movement of said shaft element to repeat, providing the desired free and flexible rocking motion.