 Complete the following phrase:  Skate skiing was introduced to competition in the 20th Century. At the first German ski championship, held at the Feldberg in the Black Forest in 1900, the Norwegian Bjarne Nilssen won the 23 km cross-country race and was observed using a skating motion while skiinga technique unknown to the spectators. Johan Grøttumsbråten used the skating technique at the 1931 World Championship in Oberhof, one of the earliest recorded use of skating in competitive cross-country skiing. This technique was later used in ski orienteering in the 1960s on roads and other firm surfaces. Finnish skier Pauli Siitonen developed a variant of the style for marathon or other endurance events in the 1970s by leaving one ski in the track while skating outwards to the side with the other ski one-sided skating; this became known as the marathon skate. American skier Bill Koch further developed the marathon skate technique in the late 1970s. Skate skiing became widespread during the 1980s after Kochs success with it in the 