NEWS FOCUS“shoulder” and the “elbow” set the arm inmotion. Walcott gave the stick-figure limb afixed amount of energy to expend and thenlet the computer search for the arm motionthat produced the longest throw.
If the computer program allowed the arm
to work against itself, it threw the object farther. The design of the arm doesn’t allow it
to chuck the object at any old angle andspeed, Walcott explains, but “doing this negative work somehow allows us to get closer”
to the optimal angle and speed.
It’s an interesting argument, says Michele
LeBlanc, a biomechanist at California
Lutheran University in Thousand Oaks, but
the abstract analysis probably isn’t the entire
explanation of countermovement. The detailsof how specific muscles, bones, and sinews
interact will also play a role, she says. Jill
McNitt-Gray, a biomechanist at the Universityof Southern California in Los Angeles, saysthat the precise function of countermovement
will probably vary even from person to person: “You and I can jump together, and how
you get your vertical impulse and how I get
my vertical impulse might be different.”

the water. That lift would supplement theforce generated by simply pushing against thewater with the palms. In recent years, researchers have questioned just how large andimportant the lift forces are, but the S-pull
has remained a standard technique among
competitive swimmers.
However, the S-pull may not
be the best pull for all races andcircumstances, says Shinichiro Itoof Japan’s National Defense
Academy in Yokosuka. Using
measurements of the lift and dragcoefficients of manikin hands anda computer model of a swimmer,
he found that the S-pull makesthe most efficient use of energy,
as it maximizes the ratio of lift todrag. It does not, however, generate the most thrust. Instead, Itofound, a straight “I-pull” yields
more pure power.
Ito had already observed something similar in his study of freshwater turtles. When paddling about leisurely,
turtles wave their feet in flourishes, doing a
reptilian version of the S-pull. When frightened, however, terrified terrapins pull theirfeet straight back to swim away as fast aspossible. Analysis showed that for turtles,
the sinuous movement was more efficient,
Ito says, but the straight movement proFor decades, competitive freestyle swim- duced greater thrust.
mers have been taught to make an S-shaped
Other familiar creatures also provide
path when pulling their hands through living examples of the advantages of thethe water. But measurements and calcula- I-pull. Underwater video shows thattions now show that to generate the maxi- Australian swimming sensation Ian Thorpe
mum thrust, swimsnaps his elbow
mers should pulland pulls his handtheir hands straightstraight through theback through the wawater, Ito says. Othter, reports a meer swimmers are folchanical engineer
lowing the nine-time
whose research wasOlympic medalist’s
inspired by his previlead, says Yuji Ohgi,
ous study of turtles.
a professor of physiSwimmers havecal education at Keiobeen purposely doing
University in Fujithe “S-pull” since thesawa, Japan. “At theearly 1970s, when
Sydney Olympics
famed swimming[in 2000], only Ian
coach James (“Doc”)
Thorpe had the ICounsilman used unshaped pull,” he says.
derwater cameras toBut now, “many, many
film elite swimmers
Australian swimmers
and found that they
do it.”
were moving their
Switching fromhand first out to theS-pull to I-pull isn’tside and then backeasy, says Ohgi, who
under their bodies. Thorpedo away! Olympic champion Ian Thorpe is also a swimmer.
By moving side to pulls his hands straight through the water.
Good swimmers
side, hands acted likegenerate power bylittle airplane wings or propeller blades, rolling from one side of their bodies to theCounsilman argued, generating hydro- other, he says, and that makes their hands
dynamic lift that pulled the swimmer through move side to side almost automatically.

CREDITS: (TOP TO BOTTOM) T. YONEYAMA/KANAZAWA UNIVERSITY; ASSOCIATED PRESS

Pulling Straight tothe End of the Poolwww.sciencemag.org

SCIENCEVOL 306

Published by AAAS

Snapshots From theMeeting
R2D2 meets K2. A robot standing 45
centimeters tall and weighing 3 kilograms swishes down a 10-meter artificial ski slope much
like a human skier,repor t engineer
Takeshi Yoneyamaof Kanazawa University in Japanand colleagues.
The mec hanicaldownhiller isn’t
completely lifelike, because it
doesn’t generatenearly as muc hforce with its legs
as humans do.
Still, the robot has
already provided
insights into why skiers move theirjoints the way they do.
A swell new wetsuit. A high-techwetsuit automatically adjusts to keep
divers warmer in cold water, reports engineer Alec Jessiman of Midé TechnologyCorp. in Medford, Massachusetts. As water flows in and out of a conventional
wetsuit, it carries away a diver’s bodyheat. But when temperatures dip, thesuit made of SmartSkin absorbs waterand swells to fill in the gaps between
diver and suit. That shuts off the flow
within minutes and reduces heat loss by
as much as 70%.
The camber of least resistance. The
tops of the wheels of racing wheelchairs
are tilted toward each other to makethem more stable. But such “camber”
also reduces the amount of rolling friction, reports Nick Hamilton, a sports engineer at the University of Sheffield, U.K.
Hamilton figured that the friction mustbe least when the wheels are perpendicular to the ground. To his surprise, hismeasurements showed that the friction
was smallest when the wheels leaned by
8 to 14 degrees, presumably because thetires deform to reduce the amount ofcontact with the ground.
–A.C.

“The I-shaped pull is rather more difficult
than the S-shaped pull because of therolling motion” of the body, Ohgi says.
Still, to shave every fraction of a second
from their times, more swimmers are tackling the challenging technique and learningto swim like a frightened turtle.

1 OCTOBER 2004

–ADRIAN CHO

43