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.

Usain Bolt Can Be Even Faster, Researchers Claim

Well, maybe Usain Bolt was right after all.  As discussed in our Physiology of Speed story, Bolt predicted he could run 100 meters in 9.54 seconds, lowering his own world record of 9.69 seconds.

Earlier this week, he almost got there running a 9.58 at the World Championships in Berlin.

Now, researchers from Tilburg University in the Netherlands say he could shave another 3/100ths of a second off and hit the tape at 9.51 seconds.

Using the "extreme value theory", Professor of Statistics John Einmahl and former student Sander Smeets have calculated the fastest possible times for men and women.  Between 1991 and 2008, they chronicled the best times for 762 male sprinters and 469 female sprinters.  They did not trust the data prior to 1991 as possibly being tainted by doping athletes (not that's its gotten much better since then.)

For females, their current world record, set by Florence Griffith-Joyner, of 10.49 seconds could be theoretically lowered to 10.33 seconds.

Extreme value theory is a branch of statistics that tries to predict extreme events such as 100-year floods or major stock market movements that deviate signficantly from the median.  With less statistical confidence (95% confidence), Einmahl estimates the men could get to 9.21 while the women could run a 9.88.

To make this statistical postulating a reality, Bolt needs to find the secret competitive edge that will shave these tenths and hundredths of seconds away. Scientists at the Research Institute of Wildlife Ecology in Austria claim sunflower oil may be the super fuel that is missing.

They found that mice fed a diet high in sunflower oil, which contains n-6 polyunsaturated fatty acids, were 6.3% faster in sprint races against mice fed a diet rich in linseed oil, which is high in n-3 fatty acids.

Their research was presented in June at the Society for Experimental Biology Annual Meeting.

"The results of the current study on mice suggest that moderate differences in dietary n-6/n-3 polyunsaturated fatty acid intake can have a biologically meaningful effect on maximum running speed", says Dr Christopher Turbill, lead researcher. "The application of this research to the performance of elite athletes (specifically those in sports that involve short distance sprints, including cycling) is uncertain, but in my opinion certainly deserves some further attention" he said.

So, a little sunflower oil mixed into the pre-race Gatorade? It might work until world records start to fall and its added to the banned substance list.

The Physiology Of Speed

Usain Bolt, the triple Olympic gold medal sprinter from Jamaica, predicted last week that he could break his own world record of 9.69 seconds in the 100 meter sprint with a time as low as 9.54 seconds.  (8/15 update: he came very close running a 9.58 at the World Championships in Berlin.)

He claimed his coach told him its possible, so he believes him. His coach, Glen Mills, may have just finished reading some new research coming out of Duke University that showed sprinters and swimmers who are taller, heavier but more slender are the ones breaking world records.

At first glance, it may not make sense that bigger athletes would be faster. However, Jordan Charles, a recent engineering grad at Duke, plotted all of the world record holders in the 100 meter sprint and the 100 meter swim since 1900 against their height, weight and a measurement he called "slenderness."

World record sprinters have gained an average of 6.4 inches in height since 1900, while champion swimmers have shot up 4.5 inches, compared to the mere mortal average height gain of 1.9 inches.
During the same time, about 7/10 of a second have been shaved off of the 100-meter sprint while over 14 seconds have come off the 100-meter swim record.

What's going on
Charles applied the "constructal theory" he learned from his mentor Adrian Bejan, a mechanical engineering professor at Duke, that describes how objects move through their environment.

"Anything that moves, or anything that flows, must evolve so that it flows more and more easily," Bejan said. "Nature wants to find a smoother path, to flow more easily, to find a path with less resistance," he said. "The animal design never gets there, but it tries to be the least imperfect that it can be."

Their research is reported in the current online edition of the Journal of Experimental Biology.

For locomotion, a human needs to overcome two forces, gravity and friction. First, an athlete would need to lift his foot off the ground or keep his body at the water line without sinking. Second, air resistance for the sprinter and water resistance for the swimmer will limit speed.

So, the first step is actually weight lifting, which a bigger, stronger athlete will excel at. The second step is to move through the space with the least friction, which emphasizes the new slenderness factor.

By comparing height with a calculated "width" of the athlete, slenderness is a measurement of mass spread out over a long frame. The athlete that can build on more muscle mass over a aerodynamic frame will have the advantage.

The numbers
In swimming, legendary Hawaiian champion Duke Kahanamoku set the world record in 1912 with a time of 61.6 seconds with a calculated slenderness of 7.88. Some 96 years later, Eamon Sullivan lowered the world mark to 47.05 seconds at a slenderness factor of 8.29.

As the athletes’ slenderness factor has risen over the years, the winning times have dropped.  In 1929, Eddie Tolan's world-record 100 meter sprint of 10.4 seconds was achieved with a slenderness factor of 7.61. When Usain Bolt ran 9.69 seconds in the 2008 Olympics, his slenderness was also 8.29 while also being the tallest champion in history at 6-feet 5-inches.

“The trends revealed by our analysis suggest that speed records will continue to be dominated by heavier and taller athletes,” said Charles. “We believe that this is due to the constructal rules of animal locomotion and not the contemporary increase in the average size of humans.”

So, how fast did the original Olympians run? Charles used an anthropology finding for Greek and Roman body mass and plugged it into his formula.

“In antiquity, body weights were roughly 70 percent of what they are today,” Charles said. “Using our theory, a 100-meter dash that is won in 13 seconds would have taken about 14 seconds back then.”
Bolt puts his prediction to the test next month at the track and field world championships in Berlin. One of his main competitors is Asafa Powell, the previous world record holder, who is shorter and has a slenderness factor of 7.85. My money is on the Lightning Bolt.