Abstract: An article of footwear includes an upper and a sole assembly secured to the upper. At least one recess is formed in the sole assembly, and a retractable protrusion is positioned in each recess. The protrusion is configured to be contained substantially within an exterior surface of the sole assembly in a retracted position and to extend substantially beyond the exterior surface in an extended position. The footwear includes at least one reservoir containing a fluid, with each reservoir having a first chamber and a second chamber. The first and second chambers are in fluid communication with one another, the first chamber is positioned inwardly of the second chamber, and the second chamber is positioned proximate a retractable protrusion.

Abstract: An article of footwear having a variable support structure includes a sole structure and an upper secured to the sole structure. At least one reservoir of magneto-rheological fluid is positioned in at least one of the upper and the sole structure. A magnet assembly is positioned proximate each reservoir, and a magnetic field produced by the magnet assembly transforms the magneto-rheological fluid from a fluid state to a near-solid state.

Abstract: A sole structure for an article of footwear includes a sole, and at least one cleat assembly pivotally connected to the sole such that a medial portion and a lateral portion of the cleat assembly can move upwardly and downwardly with respect to the sole. An upper may be secured to the sole structure to form an article of footwear.