Abstract: A treadmill has a base with a vertically displaceable platform. A mechanism is provided that resists the downward movement of the platform in response to a load applied to the platform. The mechanism also rebounds the platform upwardly with a force applied to the platform in response to a decrease of a load on the platform. A support structure enables stable vertical positioning of the platform with respect to the base.

Abstract: An article of footwear may include an upper, an outsole, and a spring plate. The spring plate may be located above at least a portion of the outsole and may extend through at least medial forefoot and medial midfoot regions. The spring plate may have an unloaded shape in which a front portion of the spring plate in a forefoot region is downwardly bent relative to a rear portion of the spring plate located rearward of the front portion. The spring plate may comprise an open central region defined by a surrounding band and may be nondestructively removable from and replaceable into the upper. The article may further include at least one inner sole member shaped to rest securely within a void defined at least in part by the upper. The at least one inner sole member may be compressible in at least first and fifth metatarsophalangeal joint regions.

Abstract: A pair of sole plates for a complementary pair of articles of footwear may generally include a first article with a first sole plate and a second article with a second sole plate, where the first sole plate is asymmetrical with respect to the second sole plate. The first sole plate includes a first groove that extends along a first lateral side of the first sole plate, and the second sole plate includes a second groove that extends along a second medial side of the second sole plate. The asymmetry of first sole plate with respect to second sole plate may improve performance, flexibility, and agility during running and in particular, during athletic events along a curved track.