Clothing closely linked to peak performance for skiers

The sport of cross-country skiing has always been preoccupied with its skis and waxing. Research now demonstrates that to shave off those extra hundredths of a second, competitive skiers should pay more attention to their clothing.

Research at SINTEF shows that what you wear is closely linked to performance. If skiers wearing modern competition skiwear want to achieve peak performance, the temperature around their bodies should be between +1 and -4 degrees. Colder or warmer than this and the time taken before they become exhausted is reduced, and performance suffers.

"The reason for this is that our average skin temperature rises and falls in step with our surroundings", says health researcher Mariann Sandsund at SINTEF Technology and Society. "If our skin temperature is too low, our muscle temperature falls, our joints and ligaments stiffen, and enzyme activity in our cells is changed", she says. "At the other extreme, high skin temperatures mean that sweat production increases.

This leads to greater fluid loss and dehydration which in turn have a negative impact on our performance". This is why it is important to wear clothing which can minimise these changes in our bodies", says Sandsund, who also heads the project "Idrett i kaldt klima" (Sport in cold climates).

Always the same ski suit
Research investigations kicked-off as early as in 2009 when several skiers from the Norwegian national team and skiing students from Heimdal and Meråker upper secondary schools were interviewed about their views on the skiwear they used during training and competition. They said that normally they always wore their ski suits, but that they would vary the layers they wore under their suits depending on the temperature.

Based on the feedback from the skiers as to what they felt functioned well and less well, researchers carried out a field study in Trondheim involving another group of eight highly-trained skiers in order to study core and skin temperatures under simulated competition conditions. They found that especially the hands, chest and thighs were subject to over-cooling.

Cold lab
The next step was to carry out a larger study at SINTEF's Work Physiology lab involving participants from the cross-country skiers group at NTNUI. These were highly-trained young people well used to stretching themselves in training and competition.

They were set the task of running on a treadmill until they were completely exhausted. The studies took place under six different temperature conditions varying from -14 to +20 degrees, and in winds of 5 metres per second. Sensors and thermometers were attached to the bodies of the participants.

"We succeeded in finding the peak performance temperature window", says Sandsund. "No-one had managed to demonstrate the relation between peak performance and temperature for cross-country skiers before," she says. "When we started our investigations we had no idea where the peak performance temperature window would be for modern ski suits", says Sandsund.

Less efficient in the cold
It was one thing for the researchers to determine the peak performance temperature window derived from measurements of how long it took a skier to become exhausted. The next was to study the impact on physiological mechanisms. They looked into how different temperatures impacted on maximum oxygen uptake, lactic acid thresholds, and what it cost the skier in terms of work economy to complete the exercise.

"Here we observed that the test individuals achieved maximum oxygen uptake regardless of temperature, but they couldn't maintain uptake over time under extreme temperature conditions. We saw that when it becomes cold it costs the body more to perform work - it simply functions less efficiently", says researcher Øystein Wiggen, who has been working on the same project.

Major source of knowledge building
Work involved with "Sport in Cold Climates" is incorporated as part of the so-called "ColdWear" project in which clothing, temperature conditions and peak performance capabilities have been common denominators in all aspects linked to petroleum industry- and sports-related studies.

Øystein Wiggen has continued his studies into sports and their relation to cold as part of his doctorate thesis, and has been looking into performance linked to double-poling techniques and upper body work in the cold chamber at the Work Physiology Laboratory. He has carried this out using both endurance tests lasting up to 20 minutes and short sprints varying from 30 seconds to 2 minutes.

"We have always wanted to make the tests more realistic, and we know of course that modern cross-country skiing is very dependent on upper body work", says Wiggen, who has run trials with test individuals in temperatures varying from +5 to -15 degrees. The results showed that performance declined by between 2 and 3 per cent in cold conditions.

In addition to Wiggen's doctorate studies, four Masters' students from NTNU have been working in this field and have made contributions to this research project. This means that the project has accumulated a significant amount of knowledge and expertise.

Swix updated
Throughout the project, Swix Sport AS has been informed of the results obtained, and has had access to a large volume of data. In 2011 the company introduced a new World Championship suit for cross-country skiers. The development of the suit was based on research generated by SINTEF.

Mariann Sandsund and Øystein Wiggen both emphasise that the project has demonstrated that modern clothing is optimal in temperatures just under 0°C, but is far from ideal under all temperature conditions.

Norwegian skiing star Petter Northug has himself said that he can't race wearing too many layers. "Perhaps we should now simply be thinking in terms of the benefits of selecting our skiwear according to the conditions", says Wiggen.