As a hobby, cross-country skiing may be viewed as a kind of "bushwalking on skis", where skiers tackle trails of various lengths and difficulties. Some skiers stay out for extended periods using tents and equipment similar to bushwalkers/hikers, whereas others take relatively short trips from ski resorts on maintained trails.
As a sport, cross-country skiing is one of the most difficult endurance sports, as its motions use every major muscle group and it (along with rowing and swimming) is one of the sports that burn the most calories per hour in execution. Modern cross-country ski competition is experiencing a revolution that is resulting in greater compatibility with audiences which began with the addition of the Sprint event to the World Cup and Olympic competitions. Today more and more races are being held in audience friendly formats, such as mass start, sprint, relay and pursuit (a race that involves switching skis and styles halfway through the race). The modern events in which athletes compete in at the World Cup and Olympics are (distances presented in Female/Male format): 1km Sprint, 2X1km Team Sprint, 10km/15km Individual Start, 15km/30km Pursuit, 30km/50km Mass Start and the 4x5km/4x10km Relay.
