Cross-country skiing is one of the most demanding of all Olympic sports, with skiers propelling themselves at speeds that exceed 20-25 km per hour over distances as long as 50 km. Yet the difference between winners and losers in these grueling races can be decided by just the tip of a ski, as a glance at any recent world-class competition will show. So just what gives top racers the advantage?

In an article to be published in the European Journal of Applied Physiology, Øyvind Sandbakk, a PhD candidate in the Norwegian University of Science and Technology's Human Movement Science Programme, reports with his colleagues on the metabolic rates and efficiencies of world-class skiers. Sandbakk's research offers a unique window on what separates the best from the rest in the world of elite cross-country racers.

"Skiers need high aerobic and anaerobic energy delivery, muscular strength, efficient techniques and the ability to resist fatigue to reach and maintain top speeds races," Sandbakk says. Those physical attributes may not be so very different from other world-class athletes, except that cross-country skiers also need to have mastered a variety of techniques and tempos, depending upon the course terrain, Sandbakk notes.

These challenges mean that the importance of the athlete's different physical capacities will differ in different sections of races, and between different types of competitions. For example, during the 10- and 15-km freestyle (skate) races in the Vancouver Olympics (the first of which are scheduled for February 15, with a 10km women's race and a 15 km men's race), skiers with high aerobic power (often referred to as maximal oxygen uptake per kilo body mass) will have an advantage in maintaining high speeds during the race, especially in the uphill terrain, Sandbakk says.

He says it is the uphill terrain that normally separates skiers the most during freestyle races. However, the 10- and 15-km courses also contain a great deal of level terrain, where an athlete with higher muscle mass and anaerobic power may have the edge needed to win.

Cross-country skiing also challenges skiers to master a great range of techniques for different speeds and slopes. Sandbakk predicts this factor will be crucial in the technically difficult Vancouver competition tracks. In skating races, skiers have as many as seven different skiing techniques (much like the gears on a bicycle) at their disposal, and they constantly shift between these different techniques during a single race.

"Skiers even adapt these seven techniques depending on the speed and slope," Sandbakk says. "The best skiers tend to ski with longer cycle lengths (the number of metres a skier moves his centre of mass per cycle), but with a similar cycle frequency," he says. "But during the last part of the race, the cycle frequency seems to be higher in the better skiers."

Another crucial aspect of technique is when the skier pushes off with his or her skate ski, and the skier's ability to recover quickly from the tremendous physical demand of providing a forceful push. "The ability to resist fatigue seems tightly coupled to the ability to maintain technique and keep up the cycle lengths and frequencies during a race," Sandbakk says. "In two skiers of otherwise equal fitness, this may be the deciding factor during the last part of the race in determining who wins the gold."

See also: The Physiology Of Speed and For Rock Climbers, Endurance Is Key To Performance

Source: The Norwegian University of Science and Technology (NTNU)  and Metabolic rate and gross efficiency at high work rates in world class and national level sprint skiers. European Journal of Applied Physiology