Photographs by Je� Wilson
THE
New insights into the biomechanics of sprinting could give athletes a leg up at the Olympics By Dina Fine Maron
SECRET TO
SPEED
B I O M E C H A N I C S
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52 Scientifi c American, August 2016
On a Friday morning this past February champion sprinter Mike Rodgers got strapped into a safety har- ness suspended from the ceiling above a custom-built tread- mill. “No one’s ever fallen, but you can be the fi rst,” he was told. Rodgers smirked and steeled himself to run. He was training for the Olympic trials. But that day he was not completing one of his standard, punishing drills on the track or in the weight room at his gym. Instead he had showed up at a small, white building in Dallas with “Locomotor Performance Laboratory” embossed on the door.
From the outside, the structure looks uninteresting, a con- verted printing shop across from a doggy day care and a yoga studio. But in recent years dozens of sprinters like Rodgers have been coming by this Southern Methodist University facility to get advice on their running technique from sports scientist Peter G. Weyand or to help him with his studies. Weyand has conduct- ed what many researchers consider to be some of the best sci- ence to date on the biomechanics of sprinting and how these elite athletes achieve their record-breaking speeds. Ahead of the 2016 Summer Olympics in Rio de Janeiro, his fi ndings have even been incorporated into training for top U.S. sprinters.
The heart of the operation is Weyand’s treadmill, a roughly $250,000 contraption outfi tted with specialized plates measur- ing the force that the runner exerts on the ground during loco- motion . Three cameras positioned around the machine capture high-speed, 3-D images of the user’s stride. Rodgers is hoping all these data will reveal insights that could help him make adjustments that would shave o� crucial fractions of a second in the 100-meter dash.
Clad in the same type of shoes, spandex top and shorts, and refl ective stickers Weyand asks all his subjects to wear, Rodgers starts to run, loping along at a little more than 6.5 miles an hour to warm up. Soon, however, he reaches more than 23 miles per hour. At this pace, the tattoo on his right calf—the cartoon Road Runner with the phrase “Catch me” inscribed below it—is a blur to the naked eye. The equipment feeds measurements into a specialized computer program that graphs his movements.
Weyand has studied more than 120 runners, including 12 other world-class sprinters—observations that have helped fi ll
in a long-standing gap in scientists’ understanding of the bio- mechanics of running at high speed. Before his investigations, the prevailing wisdom about great sprinters was that they are particularly adept at quickly repositioning their limbs for their next step while their feet are in the air. This claim stemmed largely from intuition rather than a theory based on evidence , however. Weyand was the fi rst to test this idea scientifi cally— and his fi ndings indicate that it is wrong. Instead the key to speed seems to be something else altogether, a factor that Wey- and says he can teach sprinters to improve .
ON YOUR MARK ALTHOUGH RUNNING as a sport dates back to at least 776 B.C., when a footrace was the only event in the earliest Olympic Games, the science underpinning it has long lagged far behind. Perhaps the earliest attempt to obtain rigorous data on runners came from British Nobelist Archibald Hill, who in 1927 con- ducted an experiment in which runners wearing magnets sprinted past large coils of wire that detected the magnets. Knowing the distance between wire coils, he could calculate the velocity and acceleration of the passing runners.
The invention of modern force plates in the 1950s provided the means to study another aspect of running. These devices, which resemble scales, record the amount of weight applied to
Dina Fine Maron is an associate editor at Scientifi c American
I N B R I E F
Conventional wisdom about what makes a top sprinter said that the athlete repositions his or her limbs in midair for
the next step faster than other runners. he atest fi i s indicate that, in
fact, the force with which elite sprint-
ers hit the ground plays a key role in their performance. Biomechanical analyses have revealed
the factors that contribute to force and how sprinters can augment them to achieve higher running speeds.
1
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August 2016, ScientificAmerican.com 53
them and measure it over the course of a stride. With such tools, scientists can examine the changing force exerted by a runner at di�erent speeds during a race or compare the forces from di�erent types of footfalls—those of runners who strike with their heel first versus those who strike toe first, for in – stance. Italian scientist Giovanni Cavagna gathered force data on runners in the 1970s by having them run over plates set up on a track. But because the plates are so expensive, he had just a few of them—enough to capture data from just a small frac- tion of a race. To obtain a complete run, Cavagna had to hold multiple races and manually move the plates forward after each one, recording only a few of the runners’ steps at a time, which he then cobbled together into a composite picture.
Based on those and other early studies, sprinting science focused primarily on what slows runners down—air resistance, says animal locomotion expert Jim Usherwood of the Universi- ty of London—as opposed to what speeds them up. On the whole, the work shed little light on what sprinters could do to boost their performance.
Weyand’s research has helped shift that focus and generated insights that athletes can act on. But he is not the first to envi- sion such advances. Because speed is the product of stride length times stride frequency, runners presumed that cutting down the amount of time each foot spends on the ground would net greater speed. In 2000 Weyand and his colleagues published a landmark paper showing how it is actually done. They enlisted 33 runners of varying abilities to run on an earli- er iteration of their force-plate-equipped treadmill. The results proved surprising. Weyand expected that the feet of faster run- ners would spend less time on the ground and hence more time in the air than the feet of their slower counterparts. But he
did not foresee that regardless of the runners’ abilities, they would all take the same amount of time between when a foot lifted o� the ground and when that same foot made contact for its next step.
What actually set the great sprinters apart from the rest, Weyand’s team discovered, was the force with which the run- ners hit the ground. In subsequent work, Weyand further deter- mined that at top speeds the best runners landed with a peak force up to five times their body weight, compared with 3.5 times among the average runners. That di�erence is significant be – cause like a superball that bounces higher the harder it is thrown, a runner who hits the ground with greater force stores up more energy at impact and will travel forward farther and faster as a result, with longer strides. Forceful hits also allow runners to rebound more quickly, reducing the time that feet are touching the ground and thus increasing stride frequency. The best run- ners have longer, more frequent strides.
GET SET RECENTLY WEYAND’S TEAM additionally figured out how the best sprinters are able to generate those higher forces—and in so doing forced a revision of another central tenet of the running world. According to the popular so-called spring-mass model of running mechanics put forward in the late 1980s, the legs of runners move relatively passively, working like pogo sticks to catch the body on hitting the ground and then pushing the body back into the air on rebounding. Graphical representations of the force of their footfall resemble a gentle, symmetrical curve.
But the model is based on observations of runners moving at slower speeds. When Weyand, Southern Methodist physicist Laurence Ryan and biomechanics expert Ken Clark, now at
DATA IN MOTION: Researchers at Southern Methodist University prepare American elite sprinter Mike Rodgers to run in their labo- ratory (1). To help track his movements, Andrew Udofa, a doctoral st ent, places re ecti e stic ers on o gers s leg 2 . r nner s data are automatically fed into computer programs that will help the Southern Methodist team dissect his stride (3).
2 3
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West Chester University, analyzed their video footage and force data, they noticed that the model did not seem to hold for the fastest runners. Instead of contracting and expanding smooth- ly like pogo stick springs, their legs operated more like pistons, delivering abrupt, intense hits. Force data from their footfall made a tight, tall peak.
Careful study of the lower limbs of these fast runners revealed subtle factors that contribute to the elevated forces they gener- ate: they sti� en the ankle right before they hit the ground, which serves to decelerate the foot and ankle fractions of a sec- ond after impact. This deceleration helps to maximize the force exerted on the body by the ground in response to impact and to prevent the loss of that force. Elite sprinters also keep their knees high, maximizing their distance from the ground, which gives them time and space to accelerate their footfall and ulti- mately land with greater force. The fi ndings, published in 2014, make sense logically, Weyand says: if you hit someone with a limp wrist, it will not have as much force. Yet if you keep your
wrist sti� , then you will pack a better punch, he observes. Those insights are now informing what the team says to
runners and coaches who seek their advice on how to boost sprinting performance. “It’s about simple cues. We don’t say, decelerate yourself—we say, stay sti� into the ground, and then deceleration will happen because of that,” Weyand says. A run- ner who heeds this advice will feel a harder hit to the ground with each footfall, he adds. The comportment of the rest of the body is also important, including the ankles, knees, hips, torso and head, which should also be kept sti� .
Weyand’s fi ndings have not surprised everyone. Biomecha- nist Ralph Mann, a former Olympic hurdler who now works with runners and coaches at USA Track & Field, had already been giving that type of feedback to runners, says USA Track & Field coach Darryl Woodson, who coaches eight sprinters, in – cluding Rodgers. Woodson says having concrete data support- ing Mann’s advice, however, made coaches “feel more confi dent in what they told runners.”
Graphics by Jen Christiansen, Illustration by Brown Bird Design
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F I N D I N G S
Gaining Ground What does it take to be an elite sprinter? Superb genetics and strength training play a part, but they are not the only elements of speed. In recent years studies carried out using state-of-the-art technology have yielded fresh insights into the biomechanics of sprinting that can help both professional sprinters and amateurs slash their race times.
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GO! ELITE ATHLETES WHO HAVE TAKEN Weyand’s tutelage to heart re – port improvement. Olympic hurdler David Oliver wanted to enhance his performance after he took home the bronze in his event in 2008, so his strengthening coach brought him to Wey- and in 2012. Weyand pinpointed Oliver’s two weak areas: his feet hit too far from his center of mass, and his knees were too far back—instead of parallel with or ahead of the alternate knee—which limited the force of his hits. Oliver says he focused on those problems in his training and strengthening exercises and saw a consistent improvement after several months. He went on to win the gold medal at a world championship event held in Moscow the following year in the 110-meter hurdles, and he is still fourth on the all-time-greatest list for that event.
But anecdotal reports notwithstanding, no scientific studies on these runners after they have attempted to follow Weyand’s advice have been published to date. One analysis currently under way suggests that his recommendations can bring signif- icant benefits, however. Matt Bundle of the University of Mon- tana has been analyzing how the pointers a�ect volunteer sprinters and has found improvements “on the order of the bump we think people get from performance-enhancing drugs,” he says. “It’s a pretty dramatic augmentation.”
Still, Weyand acknowledges that biomechanics are not the whole story. There are still many areas left to study and things outside of a runner’s control, he says. Genetics, for example, are clearly very important. “If you don’t have a decent build and
muscle properties that will allow you to be forceful, you won’t get [great sprinting] done,” Weyand explains. And sometimes an athlete can compensate for biomechanical shortcomings: the fastest person ever timed, Usain Bolt of Jamaica, does not execute all his mechanics flawlessly, according to Weyand. That not quite perfect form suggests that other factors must help Bolt’s game—especially his height and strength.
Sports scientists observe that Weyand’s discoveries apply not just to elite athletes but also to recreational sprinters. Maintaining a sti� ankle, getting knees higher and trying to hit the ground with great force will not make most people Olympi- ans but could help get them to a personal best, they say. Of course, hitting the ground so hard could be problematic for a recreational runner. If a person has poor form, for example, such blows could boost chances of potential injuries, including knee pain, arch pain, shin splints or a condition known as meta tarsalgia, in which the ball of the foot becomes inflamed. French researcher JB Morin of the University of Nice Sophia Antipolis recommends running downhill as part of a training regimen designed to keep ankles straight. He also suggests jumping rope to help with quick rebounding. (Weyand’s find- ings apply exclusively to sprinters. Endurance runners cannot hit the ground with as much force, because they instead need to preserve their energy over a longer time.)
For his part, Rodgers is getting good news from Weyand. In general, the best sprinters “attack the ground,” according to the sports scientist. Rodgers’s force data demonstrated that he al – ready does exactly that. Although he weighs only about 165 pounds, he hit the treadmill with more than 700 pounds of force—and that was when his muscles were tired from a prior workout. There are no guarantees at the Olympics, but if Rodgers qualifies to compete, his assessment bodes well for race day.
DECONSTRUCTING SPEED: Biomechanics expert Weyand has spent two decades trying to form a better under standing of what makes elite sprinters so fast.
M O R E T O E X P L O R E
Faster Top Running Speeds Are Achieved with Greater Ground Forces Not More Rapid Leg Movements. Peter G. Weyand et al. in Journal of Applied Physiology, Vol. 89, No. 5, pages 1991–1999; November 1, 2000.
Foot Speed, Foot-Strike and Footwear: Linking Gait Mechanics and Running Ground Reaction Forces. Kenneth P. Clark, Laurence J. Ryan and Peter G. Weyand in Journal of Experimental Biology, Vol. 217, No. 12, pages 2037–2040; June 15, 2014.
Are Running Speeds Maximized with Simple-Spring Stance Mechanics? Kenneth P. Clark and Peter G. Weyand in Journal of Applied Physiology, Vol. 117, No. 6, pages 604–615; September 15, 2014.
F R O M O U R A R C H I V E S
Fast Running Tracks. Thomas A. McMahon and Peter R. Greene; December 1978.
s c i e n t i f i c a m e r i c a n . c o m /m a g a z i n e /s a
Instead of contracting and expanding smoothly like pogo stick springs, the runners’ legs operated more like pistons.
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