Modern Nordic skiing traces its roots to the ancient forms of transportation employed by Scandinavian people to travel across their snow-covered landscapes. Nordic skiing evolved into a series of distinct competitive disciplines in the late 1800s. Cross-country skiing is at the heart of Nordic competition; in both international and the Olympic Winter Games, the Nordic events also include the biathlon (skiing and rifle target shooting), ski jumping, and the Nordic combined event (cross-country skiing and ski jumping). Nordic skiing is administered through the international governing body for all skiing disciplines, the International Ski Federation (FIS).
At its essence, cross-country skiing requires long, narrow skis with bindings that permit considerable flexibility in the movement of the foot, lightweight boots, ski poles, and clothing appropriate to the conditions; cross-country skiing can take place in conditions where the air temperature is above freezing, to those where the effect of wind chill may approach −40°F (−40°C). The skis are designed to support the weight of the skier over their greater length, creating efficiency in movement through less resistance against the surface of the snow. The skis are not fixed boards, but each is constructed with a degree of flex, which permits the skier to push with the foot and receive energy from the ski in return; unlike a flat solid surface, the ski has a significant coefficient of restitution, a physical measure as to how much energy is returned by an object from an applied force. Modern cross-country skis are made of lightweight, composite carbon fiber and fiber glass materials for this reason.
Ski conditions will vary tremendously from day to day, and occasionally from hour to hour, on a Nordic ski course, as temperatures and sunlight striking the snow fluctuate. Snow will generally be either a hard, icy surface or a softer, wetter compilation sometimes tending to slush. Specialized waxes are applied to the running surface of the skis to provide more efficient movement across the surface as well as providing the skiers with the ability to obtain a degree of traction against the surface as they stride forward.
Glide wax is often applied to the ski by way of a heat process to create maximum adhesion between the ski surface and the wax. Where the wax is applied to the surface of the ski and in what quantity it is applied are dictated by the ski conditions and the style of the skiing to be done, either classic technique or skating. Glide waxes are formulated to reduce the friction between the ski and the snow surface. Kick waxes are applied to provide the skier with grip against the snow surface. In classic ski technique, the skier strides forward with the skis moving parallel to one another. The skier strides with a kick motion, and the kick wax permits the ski to adhere to the surface long enough to create resistance, which in turn allows the skier to generate force to produce propulsion along the surface. In extremely icy conditions, a very thick wax called "klister" will be applied to the skis. Elite skiers and cross-country ski teams will have ski technicians, whose sole responsibility is to maintain the proper type of waxes for the prevailing conditions.
Classic skiing represents the original means of cross-country skiing. The skier moves with the ski propelled in parallel; the binding permits the heel of the boot to be raised with each stride. Classic skiing is sometimes referred to as "kick and glide," with the kicking motion of each foot complimented by the skier's double pole technique, with the poles being pushed into the surface with each stride for extra forward movement and for balance.
The modern form of cross country technique is the skating style. Skating skiers employ shorter skis and poles, and a motion where the skis, each positioned at approximately 30° of angle from the direction of travel, are pushed into the snow surface in a skating motion, with the poles driven into the surface in coordination. Skating permits the skier to go faster than in the classic discipline; most elite racers will compete in both types of events and, in international competition, there are races where the skier must use both techniques, with ski and equipment changes at a midway point.
The biathlon requires the skier to complete a prescribed number of laps on a course with target shooting required between laps. There is a considerable physiological and mental challenge posed in this sport, as the skier, whose heart rate may exceed 170 beats per minute while skiing, must, through coordinated deep breathing, reduce the heart rate to permit accuracy in shooting at a target positioned 55 yd (50 m) distant.
Ski jumping embraces an entirely different set of physical considerations. The athletes launch from a ramp that descends from the hill; the take-off
Cross-country skiing engages a number of important physiological considerations for the competitive racer. Fitness is crucial since cross-country skiing is a very demanding sport, requiring primarily well-developed endurance capabilities, including oxygen uptake, VO2max, to service the significant energy demands of movement. Strength-to-weight ratio is also important. Cross-country skiers are often relatively tall, to obtain a longer, more efficient stride and to secure optimal leverage with the ski poles. Cross-country skiers must possess excellent overall muscular strength, with a measure of explosive sprint capability to sprint at the end of the races.
Hydration is an important consideration as cross-country skiers will build up significant heat production and corresponding perspiration loss through the demands of the sport even in very cold temperatures. Also, acclimatization to cold and difficult conditions is essential.
Nordic cross-country ski competitions have a variety of events, from relay races to shorter sprint distances 5 km and 10 km, to the longest World Cup and Olympic event, 20 km. The courses are often designed to include significant uphill and downhill segments. Most elite cross-country skiers will compete in both classic and skating disciplines. Norway has won the most championships of any country in cross-country skiing, with Finland, Sweden, Russia, Germany, and Italy all recognized world powers in both men's and women's racing.
While cross-country skiing is at one level an elemental battle between skier and snowy course, there have been a number of doping incidents in international championships. Blood doping is the artificial enhancement of the athlete's erythrocyte (red blood cell) levels to create a greater ability to transport oxygen within the blood stream. Common techniques involve either the administration of a synthetic version of the hormone erythropoietin (EPO), which governs red blood cell production within the body, or through the intravenous transfusion of another person's enriched blood. Blood doping was the cause of a disqualification of members of the Finnish Nordic team at the 2002 Winter Olympics. In 2006 at the Turin Olympics, Russian skier Olga Pyleva was stripped of her silver medal in cross country when the banned stimulant carphedon was detected in her system.