What truly separates the best skiers in the world from the rest of the pack? A team of Norwegian physiologists set out to answer that question, taking advantage of the fact that in the last few years all of the best women on the World Cup have come from Norway.
Dr. Øyvind Sandbakk’s lab at the Norwegian University of Science and Technology gathered top six women from the 2014-2015 season – Marit Bjørgen, Therese Johaug, Heidi Weng, Ingvild Flugstad Østberg, Ragnhild Haga, and Maiken Caspersen Falla – and compared their physiology to that of six national-level competitors. The results are being published in the journal Medicine and Science in Sports and Exercise.
The national-level women had average FIS points of around 72, similar to top-20 distance skiers or top-six sprinters among the U.S. women; two of them had achieved top-15’s on the World Cup that season. Women in both groups were mostly in their mid-20’s with Body Mass Indices around 22, although the World Cup women were shorter and lighter while achieving the same ratio.
After submaximal and max-effort rollerski treadmill tests – completed just before the beginning of the 2015-2016 season – the researchers compared the women’s numbers.
In the submaximal tests, where the treadmill was set to 3 meters per second at a gradual incline for double-poling and 2.25 meters per second on a steep incline for diagonal striding, the World Cup stars were operating at a much lower capacity than the national-level women: 74 compared to 85 percent of their maximal heart rates while double-poling, or 84 compared to 94 percent while striding.
“The submaximal stages with either technique were less demanding for our WC skiers, even though the oxygen cost and skiing efficiency did not differ and the group differences in submaximal cycle characteristics were minor,” the authors wrote. “These findings are in contrast to previous observations on submaximal skiing, where the efficiency with which metabolic energy is transformed into work rate and speed together with cycle length differ between skiers of different levels of performance.”
The World Cup regulars also had lower blood lactate levels, and in diagonal striding took longer striding cycles, covering on average a quarter of a meter more per stride.
In the maximimal tests, it was apparent which athletes belonged to which group as the World Cup top-six covered both more distance (by a margin of six to seven percent) and hit significantly higher speeds during 3-minute timed tests.
In double-poling, this was because about a minute into the maximal tests the speed of the national-group skiers began to decline. The World Cup women were able to maintain their speed for about a minute longer before a drop at the end of the test. They did so by keeping significantly higher cycle rates (i.e., tempo) than the national-group skiers through the final two minutes of the test.
“In the case of [striding], neither cycle rate nor length differed significantly between the two groups, indicating that our WC skiers combine these two factors more effectively than NC skiers to achieve higher speed,” the authors noted.
The World Cup skiers also showed higher VO2Peak: 65 mL min-1 kg-1 compared to 58.8 for the national-level women while double-poling, and 70.9 compared to 65.0 while striding. Measurements of 75 and 71 mL min-1 kg-1 by World Cup skiers were believed to be the highest ever recorded by female skiers in a ski-specific exercise (as opposed to running on a treadmill, for example).
What gave rise to the differences? Any inherent differences between the athletes were compounded by differences in training. According to training diaries, the top six women reported training on average 532 hours between May and October; for the national-level skiers, that number was 411 hours. When training time during the competition season (November to April) was added in, the totals raised to 920 hours for the World Cup skiers compared to 709 for the national level skiers.
Modes of training also differed. The World Cup elite did about 26% more low-intensity endurance training than their national-level counterparts, and more mid-level and speed training but less high-intensity endurance training. The World Cup skiers also did more strength training, and their training was a stable 80-95 hours from June to October while the national-level skiers gradually increased in hours over the course of the off-season.
“Our present observation that the amounts of low- and moderate-intensity endurance training by the two groups differed provides further support for the proposal that such training constitutes the preparatory foundation for competitions in cross-country skiing,” the authors wrote. “Our present observations do not bring the importance of high-intensity training into question, although it can be speculated that in such highly trained athletes as ours, the quality of each session (i.e., optimization of physical, technical, and mental aspects) is more significant than the total number.”
One possible reason for the difference in high-intensity sessions between the two groups is that the World Cup skiers spent nearly twice as much time at elevation: on average, 42 days spent living about 1,500 meters (~5,000 feet). Time at elevation is often spent more on low-intensity than high-intensity training.
Finally, the World Cup skiers spent 33% more time running and 40% more time training skating technique, but no more time classic skiing or rollerskiing than the national-level skiers. For both groups, just over half the training time during the off-season was dedicated to ski-specific training (defined by the authors as skiing or rollerskiing), with the rest accomplished by running, cycling, kayaking, and other activities.
“This variation between sport-specific training and cross-training may help athletes to tolerate such large amounts of training during the preparation period, as well as lower the risk of injury,” the authors noted. “Our cross-country skiers varied their mode of low-intensity training considerably, whereas their moderate and high-intensity training was more ski specific.”