Roller skiing is a sport derived from snow skiing in which races are conducted on tarmac road courses with athletes wearing roller skis. The sport can be considered as an equivalent to cross-country skiing on off-snow courses. Roller skiing was created as form of training for cross-country athletes in the summer months, which later led the way for a competitive sport to be developed out of it. Roller skiing is popular in Europe and North America. Roller skis are similar in shape to that of snow skis, but have wheels on both ends, and are smaller and slightly narrower. Both the wheels on the skis are free-rolling. The skis are made of fiberglass or carbon fiber material. The boots, bindings and poles used for cross-country skiing can also be used for roller skiing. Skiers also were protective gear like helmets, knee pads, elbow pads, and full-finger gloves. Races conducted are of a variety of formats and on different types of terrain. The most common formats are individual races, sprints, team races, relays, and pursuit races. Like cross-country skiing on snow, both classic and free style races are separately conducted. The World Cup and World Championships are the two major events in which roller skiing competitions are conducted for both men and women.