For Olympic Nordic Skiers, Its All About The Glide

Friction -- or the lack of it -- in cross-country skiing events at the Winter Olympic games in Vancouver is a decisive factor in who wins the gold. Researchers at the Norwegian University of Science and Technology (NTNU) explain the physics behind what makes the best glide.

Fully seven of Norway's 11 Olympic medals to date have been won by residents of the small counties of Nord and Sør-Trondelag, which is also home to Norway's main science and engineering university, NTNU. Among the university's researchers are experts on the physical demands of cross country skiing, the physics of ski glide, physical training and the aerodynamics of ski jumping.

Felix Breitschädel, a PhD candidate at the Norwegian University of Science and Technology, has studied the interplay between the choice of skis and wax that makes a winning combination for skiers.

Cross-country skiing takes enormous physical skill and endurance -- but it also takes the right skis and the right wax to bring home the gold, as Norway's elite athletes have learned during the Vancouver Olympic Games.



The wrong wax, wrong skis or mistakes in preparation of the base of the ski, "might lead to a change for the worse by up to 3 per cent," he says.

Cross-country skiers are able to kick and glide because of the way the wax and the physical structure of the ski and its base interact with the snow. When the skier presses down on one ski during a kick, the wax and ski base grip the snow, enabling the skier to push off and glide on the other ski.

Breitschädel, who is in Vancouver with the Norwegian national team, says ski preparation specialists that travel with racing teams have developed a four-step process that helps them decide how the skis should be prepared and what will work best. The steps are:

1) Different skis are tested on the track the day of the race to see what works best.

2) Once a ski itself has been chosen, the prep specialists go to work to create a micro structure on the ski base that will work in specific snow conditions. This structure is tested prior to the race.

3) Just a few hours before the race, the prep specialists have to test different waxes and wax combinations and wax the skis, which are then tested.

4) Just minutes before the race, the base of the ski is fine-tuned.

Breitschädel reports that the weather and track conditions at the Whistler Olympic Park in the Callaghan Valley are very special. "The arena is located 10 km west from Whistler, and about 200 km from the Pacific Ocean, and the area gets an average snow fall of 10 m in the surrounding mountains," he says. "Currently, the average snow depth is 1.2 m at the Nordic area."

Even though the site is not directly on the coast, it is still affected by coastal weather he says. The average temperature in February has been + 0.6°C, far warmer than the -1.4°C that has been the 4 year February average temperature.

But as long as there is enough snow, why does snow temperature matter to skiers? Breitschädel, says the mild temperatures in combination with regular showers increase the speed at which the snow changes structure, transforming pointy freshly fallen snowflakes into rounded snow grains. Regular freeze-thaw cycles further increase the snow grain size. Clusters of wet and round bonded snow crystals are the consequence.

Because the ski slides on the snow, the actual amount of surface area on the ski base is one important factor that determines how much friction there is.

If there is too much real surface contact area, the skier will actually experience some suction under wet conditions, but if it is colder, lots of surface area generates enough frictional heat to generate a thin water film for the ski to glide on.

"The ski base structure has to fit to the given snow grain condition," Breitschädel says. "New snow, with its complex snow crystals, requires a different ski base structure than old transformed snow grains." That means cold conditions call for fine grinds while coarse grinds are best for wet snow.

But what of the disappointing results for the Norwegian men's team in the 15 km freestyle race during the first week of the Winter Olympics? After race favourite Petter Northug turned in a disappointing finish, Norwegian media speculated that the wax might have been wrong. Breitschädel says that's an overly simplistic assessment.

"Waxing is one out of four parameters which affect the total performance of a ski. In addition to the ski characteristic, structure and track conditions, the waxing and the final ski tuning with a manual rilling tool are all important," he says. Each team carefully guards its wax and ski structuring secrets, but mistakes happen. The 3 per cent decrease in performance wouldn't make much of a different for the average skier, he says, but "at such a high level they are crucial and can make the difference whether an athletes wins a medal or not."

See also: Vancouver Olympians Prepared For High And Low Altitudes and Aerobic Efficiency Is Key To Olympic Gold For Cross-Country Skiers

Source: The Norwegian University of Science and Technology (NTNU).

Vancouver Olympians Prepared For High And Low Altitudes

Lindsey Vonn winning gold

For winter sports athletes, including Olympians competing in Vancouver this week, the altitude of the sports venue can have a significant impact on performance, requiring athletes in skill sports, such as skating, ski jumping and snowboarding, to retool highly technical moves to accommodate more or less air resistance.

When considering the challenges and benefits of training and performing at sea level verses altitude, people often think of the effect altitude can have on oxygen delivery to muscles -- at higher altitudes, the body initially delivers less oxygen to muscles, which can result in fatigue occurring sooner during exercise. Higher altitudes also have less air density -- about 3 percent reduction for every 1,000 feet -- which can result in faster speeds in ski and skating races due to less aerodynamic drag, but can also affect timing and other technical components in skill sports.

"Many athletes perform thousands upon thousands of moves so they get a certain motor pattern ingrained," said Robert Chapman, an expert in altitude training at Indiana University. "A different altitude will change the feedback they get from balance and proprieception. In an endurance sport such as cross country skiing or biathlon, for competition at altitude it takes about 10-14 days to adjust. For a skill sport, it's harder to judge how long it will take to acclimate to the reduced air density at altitude. Hopefully, these athletes have incorporated this into their training, maybe in the last year or for a period of time, not just the two weeks leading up to competition."

Chapman, an exercise physiologist in the Department of Kinesiology in IU's School of Health, Physical Education and Recreation, wrote about the topic in a special Winter Olympics issue of the journal Experimental Physiology.

The Winter Olympics are being held in Vancouver, British Columbia, which is practically at sea level. The ice events also are nearly at sea level, with other venues ranging from altitudes of around 2,600 feet for the sled events to around 5,000 feet for women's and men's downhill skiing.

Shaun White enjoying some altitude

Chapman said fans should expect few record times in speed skating events because of the low altitude and greater air resistance facing athletes. He and his co-authors note in their paper that current world records for men and women in every long-track speed skating event from the 500-meter to 10,000-meter races were set in Olympics held in either Calgary, at an altitude of 3,400 feet, or Salt Lake City, with an altitude of 4,300 feet. They note that every Olympic record for all individual event distances was set at the 2002 Olympic Games in Salt Lake City, with none topped in the 2006 Winter Olympics held in Turin, which lies at an altitude of 784 feet.

"The general thought is that altitude slows you down because you have less oxygen going to your muscles," Chapman said. "But at altitude, just as it is easier to hit a home run in the thin air of Denver, speed skaters in Calgary and Salt Lake City could skate faster, move through the air faster, because there was less drag. Eight years after Salt Lake City, we have natural improvements that you'd expect to see involving training, coaching and technology, but we won't see many records in Vancouver. It doesn't mean the athletes are worse, if anything they're probably better. It's the effects of altitude on athletes' times."

Air density can have a dramatic effect on ski jumping, he said, requiring athletes to change the angle of their lean depending on the altitude. Chapman said the women's and men's Olympic downhill skiing, freestyle skiing and snowboarding events take place at higher altitudes this month and could require technical adjustments by the athletes.

Chapman and his co-authors make the following recommendations concerning training and performing at altitude:

• Allow extra time and practice for athletes to adjust to changes in projectile motion. Athletes in sports such as hockey, shooting, skating and ski jumping may be particularly affected.
• Allow time for acclimatization for endurance sports: Three to five days if possible, especially for low altitude (1,640-6,562 feet); one to two weeks for moderate altitude (6,562-9,843 feet); and at least two weeks if possible for high altitude (more than 9,843 feet). Chapman said altitude affects breathing, too, with breathing initially being harder at higher altitudes.
• Increase exercise-recovery ratios as much as possible, with a 1:3 ratio probably optimal, and consider more frequent substitutions for sports where this is allowed, such as ice hockey. Recovery refers to the amount of time an athlete eases up during practice between harder bouts. If an athlete runs hard for one minute, following this with three minutes of slower running would be optimal before the next sprint. The recovery period gives athletes more time to clear lactic acid build up from their muscles.
• Consider the use of supplemental oxygen on the sidelines in ice hockey or in between heats in skating and Alpine skiing to help with recovery. Chapman said this helps calm breathing, which can be more difficult at altitude.
• Living at high altitudes while training at low altitudes can help athletes in endurance sports improve performance at lower altitudes.

See also: Wind Tunnel Is A Drag For Olympic Skeleton Riders and Aerobic Efficiency Is Key To Olympic Gold For Cross-Country Skiers

Source: Indiana University and Altitude training considerations for the winter sport athlete. Experimental Physiology

Aerobic Efficiency Is Key To Olympic Gold For Cross-Country Skiers

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

Wind Tunnel Is A Drag For Olympic Skeleton Riders

Noelle Pikus-Pace of the USA Olympic Team

Olympic skeleton athletes will hit the ice this week in Vancouver, where one-hundredths of a second can dictate the difference between victory and defeat.  Using state-of-the-art flow measurements, engineering professor Timothy Wei and students at Rensselaer Polytechnic Institute in Troy, N.Y., are employing science and technology to help the U.S. skeleton team trim track times and gain an edge over other sliders.

"Not much is known about the actual mechanics of skeleton, so we developed a unique suite of tools to help pull back the curtain a bit," said Wei, head of Rensselaer's Department of Mechanical, Aerospace, and Nuclear Engineering, who has previously worked with U.S. Olympic swimming coaches and athletes. "Even in the short time since developing the system, we have learned a whole lot more about how the athlete's suit, helmet, body movements, and positioning affect aerodynamics."

"The real-time aerodynamics work that Rensselaer has provided for us has helped to fine-tune our athletes' body positions and equipment in a way that we've never experienced before," said USA Skeleton Technology Coordinator Steve Peters. "These new concepts will give our athletes the data they need to remain competitive with the rest of the world."


Lying face-down, and hitting speeds of more than 70 mph (112 kph), skeleton athletes maneuver their sleds down an icy, mostly-covered track rife with twists and turns. Skeleton sleds feature no steering or braking mechanisms, so body control and balance are critical for navigating the tracks. A relatively young sport, skeleton was permanently added to the Olympic program in 2002. Skeleton is rigorous on an athlete's body -- the vibrations and bodily stress are so intense that even Olympic contenders usually cannot slide more than four times per day, making it difficult to collect data.

So Wei set out to build a system that accurately simulated an actual skeleton run, while collecting as much data as possible. The professor understood that the more drag, or wind resistance, an athlete creates, the slower he or she is going to slide, so Wei needed to find a way to examine all the different variables: the clothing, headgear, and body position of sliders, as well as the skeleton sled itself. Studying drag requires wind, and the skeleton sled was slightly too large to fit into either of Rensselaer's two wind tunnels. The jet of air exiting the exhaust vent of the wind tunnel, however, worked perfectly.

Wei and his students created a replica section of a skeleton track directly behind the wind tunnel. They built sensors into the floor of the replica, onto which they placed a skeleton sled. Each sensor was fit with an oscilloscope, and sent digital data to a nearby computer that calculated the sled's pitch, roll, and balance -- technical terms for indicating if the slider is leaning backward, forward, left, or right. The sensors also measured wind resistance, or drag.

With a skeleton athlete lying on a sled in the test track, Wei turned on the wind tunnel. The steady stream of air exiting the wind tunnel's exhaust replicated the conditions of an actual skeleton run. Wei and his team cut a hole in the bottom of the test track, slid in a computer monitor, and covered the hole with clear plastic. This allowed the athletes to view, in real time, data and graphs clearly illustrating the impact that every little lean or tilt had on wind resistance, and thus on their speed.  One side wall of the track was also made from clear plastic, allowing coaches to observe the tests.

Wei and Peters brought 10 different skeleton athletes to Rensselaer for a test run on the new system. They tested a wide variety of skeleton suits and gear, some of which, Wei said, certainly created more drag than others.  "This is more information than these athletes have ever had about the impact of what they're doing while sliding," Wei said. "It was a real eye-opener for them."

To further test the athletes, suits, and headgear, Wei also developed a state-of-the-art diagnostic tool using a video-based flow measurement technique known as Digital Particle Image Velocimetry (DPIV). He bounced a green pulse laser off a cylindrical lens to create a thin sheet of light, which he shined over the shoulders of athletes laying the test system. Wei then introduced theatrical fog into the front of the test bed.

Wei videotaped the fog as it was pushed around by the wind tunnel exhaust, and then used sophisticated mathematics, computer modeling, and stop-motion video to track the behavior of the swirly fog as it rolled off the bodies and heads of the athletes. This data, he said, can be used to identify vortices, pinpoint the movement of air, and hopefully identify new and more detailed methods for skeleton athletes to reduce their drag.

Meanwhile, a team of undergraduate students in the O.T. Swanson Multidisciplinary Design Lab (MDL) at Rensselaer looked at different engineering techniques to help improve the skeleton sleds. They developed a data acquisition system for the sleds, which measured specific mechanical properties of the sled in real-time as the athlete guided it down the track. One component of this system is a camera that attaches to the slider's helmet, providing athletes and coaches with a new proof-of-concept tool from which to learn.

Wei is no stranger to applying science and technology to the world of sports. He has been working with USA Swimming for several years, using DPIV and other techniques to better understand how swimmers interact with the water. He also created a robust training tool that reports the performance of a swimmer in real-time, measuring how much energy the swimmer exerts with each kick. The tool helped several top-tier athletes trim seconds from their lap times.

Wei said he's confident that the United States will have a strong showing in skeleton in Vancouver, and that he's looking at ways to improve his technology to be even more effective when training swimmers to compete in the 2012 London Olympics and skeleton athletes to compete in the 2014 Winter Olympics in Sochi, Russia.

Source:Rensselaer Polytechnic Institute.

Swiss Team Bobbing For Gold In Vancouver

Switzerland has a long tradition of bobsledding and the Swiss Bobsleigh Federation has a remarkable record at international competitions. Currently, Switzerland even boasts two reigning world champions: Ivo Rüegg in the two-man bob and junior world champion Sabina Hafner. Moreover, pilot Beat Hefti won last year’s world cup season – also in the two-man bob.

To be better than the rest, the athletes not only need talent and experience, but also a fast bobsled. No one knows this better than former bobsledder and leader of the “CITIUS” project, Christian Reich: “for a pilot, being able to rely on a strong team and fast equipment is the key to good performance.”

Consequently, three years ago a joint venture between the Swiss Bobsleigh Federation (SBSV), researchers from ETH Zurich and Swiss industrial companies set about building a high-speed bobsled from scratch. “We wanted to build a bobsled that was faster than the competition because in bobsledding you can’t afford to sit back”, explains Peter J. Schmid, Central President of the SBSV.

The project was named “CITIUS” after the motto of the Olympic Games, “Citius, altius, fortius” (faster, higher, stronger). Last Fall, after thousands of hours of development and numerous trials in the wind tunnel and on the ice track, the developers and federation representatives handed over the new high-tech sled to the Olympic bobsled squad in front of the media.

Eliminating brake sources

As far as ETH Zurich was concerned, about two dozen researchers from the Departments of Mechanical Engineering, Process Engineering and Materials Science were involved in the development of the bobsled. It was their job to refine the material whilst keeping to the specifications of the International Bobsleigh Federation and optimize the runners, aerodynamics, stability and vibrations.

Professor Ueli Suter, Program Coordinator at ETH Zurich, said that, “For a vehicle without an engine that hurtles down an ice track at 150 km/h, finding all the important brake sources, then eliminating them and still producing a safe piece of equipment for the athletes is a complex interdisciplinary undertaking.”

Extensive industrial expertise sought
The results of the research conducted at ETH Zurich were passed on to project supervisor Christian Reich, who in turn passed them on to the development, training and production workshops of the specialist industrial companies (see box). Dr. Jürg Werner, the head of V-Zug AG’s development department, said, “The industrial partners involved contributed their expertise to the project because they feel an affinity to Swiss bobsledding. The collaboration with ETH Zurich and among industrial partners resulted in a welcome transfer of knowledge. CITIUS stands for innovation, as do the industrial partners involved.”

The countdown is on!
A total of six two-man bobsleds and three four-man bobsleds of the “CITIUS” model have been constructed and are ready to compete for hundredths of a second. The final test runs are scheduled for the second half of October in Cesana/Turin before the Swiss pilots are given their first and only opportunity to train with the new bobsleds on Whistler’s Olympic bobsled track. Shortly afterwards, the world cup season gets underway with the first race in Park City.

The bobsled competition at the Winter Olympics in Vancouver will be held from February 20 – 27 2010. By then at the latest, we should know whether the big efforts of all those involved in the “CITIUS” project have paid off and whether Switzerland can add to its medal collection as a bobsledding nation.

Source: ETH Zuerich