Science at the Winter Olympics

Dozens of University of Minnesota students and alumni are in Italy to compete in the XXV Olympic Winter Games, whose opening ceremony is Friday, Feb. 6.

Beneath Olympic athletes’ natural abilities and hard work lies a bedrock of science that has led to improvements in safety, performance, and the sheer enjoyment of sports. University of Minnesota Twin Cities experts provide glimpses at the science behind Winter Olympics sports.

Curling throws physicists a curve

Curling is well named. In this sport, players slide several polished granite “stones” — each weighing 38 to 44 pounds — onto an “ice sheet.” They try to get one or more of their stones to stop closer to the center of the “house” — a bull’s eye at the far end of the sheet — than any of the other team's stones.

The player who “throws” a stone — slides it by hand onto the ice — gives the stone a curling motion. What happens next gives the physicists their own workout.

“The goal is to get just the right velocity and spin,” says curling enthusiast Ryan Elliott, a professor in the Department of Aerospace Engineering and Mechanics. After the initial "throw," curling stones, he says, naturally curl in the direction of their spin. That is, a stone with a clockwise spin will curl to the right, and vice versa. 

"Why stones curl has long been a mystery," Elliott says. 

Players can only change their stones' trajectories by sweeping the ice near them, using special brooms with fabric heads. This creates friction, which generates heat to melt some of the ice and smooth the stone’s path to the house — or to a collision with another stone. The target stone could be one of their own, to improve its position, or an opponent’s, to knock it off course. 

“Olympic-level sweepers can add five meters to the distance a stone travels,” Elliott notes. 

The bottoms of stones have rough, circular “running bands.” These increase friction beneath the front and rear edges of a moving stone.

“The physics argument is that rough stone produces ice grooves,” Elliott says. “The leading edge of the rough circle produces diagonal grooves in the ice. Next, the back edge gets into those grooves and is guided to move along the grooves and curl. 

“It’s accepted [among researchers] that this is part of the mechanism by which stones curl.”

Curling stones are made of granite from the isle of Alisa Craig, off the southwestern coast of Scotland. This granite’s unique crystal structure allows it to form tiny cracks that absorb energy during collisions, extending the stone’s endurance and lifespan. Up to a point.

“The limit is usually 10 to 15 years,” Elliott notes.

Overall, “it’s very complicated,” he muses. “It’s not rocket science. It’s harder.” With all these elements at work, and 16 stones in play at once, it’s no wonder curling has been called “Chess on Ice.”

Eight athletes with University of Minnesota Duluth or Twin Cities connections will be competing for Team USA in curling.

Hockey and body fat

As the University's faculty athletic representative to the NCAA and the WCHA, Donald Dengel will be watching many of the female athletes he follows as they compete for hockey gold.

A professor in the University's School of Kinesiology — where research and teaching concern human movement, performance, and function — and editor of the International Journal of Sports Medicine, Dengel led a study with NCAA Division I hockey players to answer the question: Who skates faster, forwards or defensemen? 

For this he had athletes of both sexes skate a 148-meter course on a rink (see diagram). It began at one end with a zigzagged section where skaters had to quickly change direction, then continued with a linear course around the opposite goal and back. Times were automatically logged at several “gates” along the course.

Dengel’s team also measured the skaters' body fat and lean mass with dual X-ray absorptiometry, a noninvasive, low-radiation imaging test. 

The statistics showed that speeds were not significantly different between forwards and defensemen of either sex. From this, “One can see the premium placed on skating ability,” Dengel says. 

Also, the total body fat percentage was correlated with skate times in both sexes — that is, a higher percentage predicted longer times and thus slower speeds. This, says Dengel, “ shows the importance of body composition and the need for coaches, trainers, and athletes to measure body composition in this sport.”  

As for this Olympiad, “Hockey will be interesting, since the rink is not the standard NHL size rink,” Dengel notes. “There has been some complaining about this. The rink is basically shorter and wider than NHL rinks, which may lead to more high-speed collisions between players.” 

Staying warm — but not too

Male and female alpine skiers get exposed to some of the most extreme combinations of low temperatures and oxygen. In this Olympiad, they start their runs at elevations of 1.4 and 1.48 miles, respectively. Runs typically last less than two minutes, so staying warm isn't too hard. 

Also, “Oxygen availability isn’t much of a problem,” says Daniel Craighead, an assistant professor in the School of Kinesiology. For one thing, he says, our bodies normally store “a few seconds’ worth” of ATP, the principal energy “currency” in our cells. Also, the early stages of glucose digestion can produce a little extra ATP in temporarily oxygen-starved cells. Completing the digestion will, however, require oxygen. 

If you’ve noticed the blood vessels in your hands shrinking in the cold, it’s your skin’s automatic thermoregulation system at work.

“We have thermoregulatory nerve endings in the muscle of our blood vessels,” Craighead says. “They message the brain, which sends a signal directing [the muscle surrounding the blood vessels] to constrict.”

Some of the biggest challenges face cross-country skiing and biathlon competitors.

"These skiers are in the wind, so they’re at risk of inadequate heat production," Craighead says. And they must avoid sweating so much that they get chilled when the sweat evaporates.  

"But it's also a matter of clouds versus sun," he adds. "They have to take all factors into account. It's important that they dress for the conditions."