What are the physiological capacities of nordic-combined athletes and can laboratory tests predict performance capabilities on the World Cup?
Those are the questions that a team of Norwegian researchers set out to answer by testing 12 competitors from eight different countries before a 2015 World Cup competition in Trondheim, Norway.
The study, led by Vegard Rasdal of the Norwegian University of Science and Technology and the Norwegian Olympic Sports Center, was recently published in the academic journal Plos One. It is an open-access journal, so you can read the paper here.
“The sport is always evolving,” Rasdal wrote in an email to FasterSkier about the results. “Today it is no longer enough to be ‘just’ a strong ski jumper or cross-country skier, you really have to excel in both in order to be successful in terms of podiums. Johannes Rydzek and Eric Frenzel, the two most successful athletes last season, were not only two of the best jumpers last season but also the fastest skiers.”
Indeed, they found that the best skiers in the nordic combined field have VO2Max capacities close to those of the best cross-country skiers, period – and even higher than those of Olympic medalist sprinters. Furthermore, this was a good predictor of World Cup results in the Trondheim competition.
Variability in Abilities and Physiology
There have been plenty of physiological studies on top cross-country skiers and some on ski jumpers, but the fascinating aspect of nordic combined is that two very different sports are combined. That creates uncertainty about what the ideal physiology for a competitor might actually be. Should they be light and explosive, for jumping? Strong and enduring, for skiing?
And do nordic-combined atheltes have as much explosive power as ‘special jumpers’, or as high aerobic capacities as cross-country skiers?
“As with most endurance sports, you will find a strong association between VO2Max and performance when the study group is heterogeneous, as e.g. a study group of 200 college students,” Rasdal explained. “Overall, VO2max is widely accepted as the most important factor for endurance performance. However, in a more homogenous study group, such as elite cross-country skiers, all athletes may have a ‘high enough’ VO2max to perform well at an elite level. Thus, other factors such as skiing efficiency becomes a stronger determining factor.”
Rasdal and his co-authors wondered whether nordic-combined athletes fell into the first group, with moderately variable VO2Max, or the second group, where all had such high capacity that they had to be distinguished by some other characteristics.
Because some athletes get their start in ski jumping, and all must also train for jumping, the athlete selection process and training background from young ages is different than for cross-country skiers and could lead to more variability among individuals.
“It is not given that all nordic combined athletes have a ‘high enough’ VO2max or vertical jump capacity,” Rasdal wrote. “The shortcomings in one may to some degree be compensated with higher level in the other.”
To address that question, the research team partnered with the International Ski Federation (FIS) to conduct laboratory tests on athletes the day before a World Cup competition.
“FIS was responsible for the invitation of athletes, and each nation in the World Cup was invited and encouraged to participate with two athletes to be tested,” Rasdal explained. “To collect data on the very best athletes in the world is always a challenge, especially so close to an important international competition. We as a research group are extremely grateful that so many World Cup athletes chose to participate in the data collection.”
The athletes ran the gamut from being ranked second to 66th in the previous season’s overall World Cup standings, and included the eighth-best skier and second-best ski jumper.
About Endurance Capacity, and World Cup Success
The hypothesis that nordic-combined athletes were more variable in their physiology compared to single-sport specialists was largely upheld.
“Among the athletes we studied, a VO2peak range of 66.9-80.8 could be found, which does illustrate the heterogeneity in nordic combined,” Rasdal wrote. “This may make subordinate factors such as skiing efficiency relatively less important (although still important) than VO2peak.”
The upper measurements of VO2Max among the 12 athletes are close to those of cross-country skiers.
“In the papers by Saltin and Åstrand (‘Maximal oxygen uptake in athletes’) and Tønnessen et al. (‘Maximal aerobic capacity in the winter Olympic endurance disciplines: Olympic medal benchmarks for the time period 1990-2013’), only a few athlete-groups possess VO2Max values above 80 ml/kg/min,” Rasdal noted.
Furthermore, it was clear that the athletes on the lower end of the VO2Max spectrum were somewhat less successful on the World Cup. At least at this World Cup event, the overall ranking at the end of the day was strongly correlated to an athlete’s VO2Max and ski performance.
“This study together with the study by Tønnessen et al. may indicate that a body-mass normalized VO2Max in the region of 75 ml/kg/min is a sufficient capacity for a strong cross-country performance in Nordic Combined, whereas 80 is at very highest percentile,” Rasdal explained.
However, the Trondheim World Cup course is not necessarily representative of all World Cup venues. And poor cross-country skiing could have been penalized even more at this venue than usual.
“Trondheim is a special arena compared with other courses in the World Cup, with many steep uphills and fast downhill terrain,” Rasdal wrote. “In addition, 2015 was a bad winter in Trondheim, and the course was salted and ice hard. This made the event well suited for technical good skiers with strong upper-body capacity. It is therefore necessary to investigate the impact of ski jumping versus cross-country skiing on overall performance, as well as the associations to laboratory capacities, also at other venues and conditions.”
And About Those Jumps
The implication is that perhaps at a different competition, the association between ski jumping performance and overall competition ranking might be stronger.
“Unpublished data does show that [across a whole season], the regression line for ski jumping to overall performance is similar to that of cross-country and the correlation coefficients are similar,” Rasdal explained.
When it came to benchmarking, the researchers also identified laboratory measurements that could predict ski jumping performance by nordic-combined athletes. They tried two measurements: a straight, simple squat-jump, and an “imitation jump” where the athletes were asked to start in the same position they would on a ski jump ramp. The jumping style and technique varied from athlete to athlete.
While it seems logical that these would be good predictors of ski jumping performance, it actually wasn’t a trivial matter. Such measurements have mainly been validated on straight ski jumpers, and because of their different body mass and physiology the relationship between squat jumping and performance, for example, could very well have been different among nordic-combined athletes.
“The time available at the take-off in the [ski jump] hill may present a greater challenge for NC athletes than specialist ski jumpers as two-thirds of the NC athletes’ annual training consists of endurance training,” the authors wrote in the paper. “This does not only leave less time available for power and [jumping-] specific training compared to the specialists, but endurance training may lead to negative effects on muscle strength and power.”
But in the end, the same measurements did predict ski jump performance.
“The jump capacity in the sport-specific imitation jump distinguished performance level better than the general jump capacity in squat jump,” Rasdal wrote. “That supported the argument for sport-specific testing at an elite level.”
Still, the imitation jump wasn’t perfect at predicting actual ski jump performance.
“The upper range of the lowest ranked performance group touches the lower range of the highest ranked performance group,” Rasdal said of the imitation jump measurements. “There is not necessarily a continuous linear relationship with performance. At some level, the ability to utilize the capacity in the field as well as other factors become more determining for performance, e.g. body mass, transition to flight (minimize the loss of speed), flight performance, etc… Ski jumping is an extremely challenging technical task to be performed in less than 0.35 seconds, and where a well execution may compensate more for a lack of physical capacity.”
And then there’s money.
“In ski jumping the equipment plays an important role, and the nations with the highest budgets may for instance have better suits which makes them jump farther,” Rasdal said of other potentially confounding factors in predicting jump performance.
What to Shoot For
At the end of the paper, the authors summarized the ideal characteristics of a nordic-combined athlete: high VO2Max, a strong upper body, a good vertical jump, and low body mass. Hitting all those different metrics at the same time is a tough calculus, but it’s what is required to be a champion these days.
“Although the relative importance of ski jumping to overall performance has varied in the sport over time, the pendulum today appears to lean more towards ski jumping,” Rasdal noted. “That’s both as a result of regulations (e.g. increase of meter-value in large hills in 2015), and also an increase in overall performance level where the best ski jumpers also ski fast.”
Chelsea Little is FasterSkier's Editor-At-Large. A former racer at Ford Sayre, Dartmouth College and the Craftsbury Green Racing Project, she is a PhD candidate in aquatic ecology in the @Altermatt_lab at Eawag, the Swiss Federal Institute of Aquatic Science and Technology in Zurich, Switzerland. You can follow her on twitter @ChelskiLittle.