The undersole of a shoe is provided with openings, above which are mounted housings for respective spike members. Each spike member includes at least one spike mounted on an edge of a carrier, a slide, and a hinge between the carrier and the slide. The slides are slidably mounted in the housings. The carriers and housings have slidingly engaged curved surfaces which turn the spikes on the spike carriers from being generally horizontal when the spikes are withdrawn into the undersole, to being generally vertical when the spikes are extended. An operating mechanism, preferably a battery-operated electric motor-powered mechanical drive moves the slides to extend and retract the spikes.