Abstract: A ski has an elongated body part, a polyethylene bottom layer arranged on the body part, and a roughening provided on a sliding surface of the bottom layer over a supporting length of the ski and including a plurality of projections each formed as an elongated tooth from polyethylene of the bottom layer and inclined in its entirety toward the rear end of the body part, wherein the teeth are arranged with a density of between 1000 and 4000 teeth per cm.sup.2. The inventive ski is manufactured by dry grinding of the sliding surface of the polyethylene bottom layer with a relatively high efficiency.

Abstract: A tennis racket includes a handle portion, a frame portion which has strings mounted therein and a throat portion which connects the handle portion and the frame portion. An insert is installed in the throat portion and connected to the same. The insert is adapted to have secured thereto at least some of the strings. The insert may undergo elastic yielding in direction substantially normal to the general plane of the frame portion in response to the impact of a ball onto the strings and consequent transmission of the impact stress from the strings to the insert.

Abstract: A ski is described which has a running surface and a profiling transverse to the longitudinal axis of the ski in at least one region of the underside of the ski intermediate the tip and the rear end of the latter. The ski comprises a rifling of grooves extending transversely to the longitudinal axis of the ski, in the aforesaid region of the underside of the ski, which rifling constitutes at least part of the transverse profiling. Preferably, the portions of the ski underside adjacent the rifled region and up to the tip of the ski, on the one hand, and up to the rear end of the ski, on the other hand, are smooth. Methods for producing the ski are also described.