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New study: Running mechanics, not metabolism, are key to performance for elite sprinters

Sprinting performance isn’t a factor of conserving energy; rather, forces applied by the foot hitting the ground maximize all-out bursts of sprinting

Sprinters competing in the 2012 Olympics might assume their championship performance is the result of their fuel-efficient physiology.

But a new study disproves the classic scientific view that conserving energy maximizes performance in a sprinting event.

The study by biomechanics researchers Matthew W. Bundle at the University of Montana and Peter G. Weyand at Southern Methodist University, Dallas, demonstrates that metabolic economy is not an important factor for performance in events lasting 60 seconds or less.

In fact, just the opposite is true.

“That prevailing view is no longer viable,” said Weyand. “Sprinters, if anything, are wasteful of energy. This is due to the biological trade-offs between faster muscle fibers that provide the large and rapid forces needed for sprinting, and slower muscle fibers that maximize metabolic economy.”

Instead, the key to top-flight sprinting is to maximize how hard each foot hits the ground, which allows sprinters to translate musculoskeletal and ground reaction forces into swift motion, said Bundle.

“Saving energy is critically important for endurance, but not for sprinting, which our findings indicate is not energy-limited,” Bundle said.

Metabolic energy available from sustainable, aerobic sources predominantly determines performance during endurance events by setting the intensity of the musculoskeletal performance that can be sustained throughout the effort, the study found.

For sprinters, Bundle and Weyand conclude the opposite is true.

“The intensity of the mechanical activity that the musculoskeletal system can (for a very short time) achieve determines the quantities of metabolic energy released and the level of performance attained,” according to the study.

The authors reported their findings in “Sprint Exercise Performance: Does Metabolic Power Matter?” in the July issue of Exercise and Sport Sciences Reviews.

Sprint performance variations are a function of external forces
The authors write in their study that athletic performance can be analyzed considering either the input to, or the output from, the skeletal muscles that serve as biological engines. Input is the chemical energy that fuels muscular contraction. Output is the force or mechanical power the contractions produce.

To analyze the mechanics of burst-type sprint activities, the authors said they drew on all-out running speeds and cycling power outputs of humans because of the abundance and quality of the data available and because the mechanical and metabolic contrasts between the two provide informative insights. The authors focused on durations of up to five minutes, particularly on efforts of less than a minute.

For both exercises, differences in sprinting performance were predominantly a function of the magnitude of the external forces applied because running contact lengths and cycling down-stroke lengths, as well as stride and pedal frequency, exhibited limited variations. Additionally, for both cycling and running, external forces applied during sprinting are believed to be consistently related to the corresponding muscle forces, regardless of the intensity or duration of the effort.

So what determines the maximum external forces the musculoskeletal system can apply during a brief, all-out sprint? And why do those forces decrease over the duration of the sprint?

The researchers assessed neuromuscular activation using a diagnostic procedure called surface electromyography to measure electrical activity in the activated muscle fibers. That assessment showed that neuromuscular activation increases continuously during all-out sprint cycling and running trials. More rapid increases were typical for the briefest trials that required the greatest forces. That indicates that all-out sprinting performances are highly dependent on duration because of the speed of musculoskeletal fatigue during dynamic exercise requiring large force outputs, the authors reported.

Sprint performance linked to mechanics of applying external force
Bundle and Weyand altered three independent variables to maximize the variation observed in sprint performance: Subjects were individuals with large differences in their sprint performance capabilities; all-out sprint trials spanned a broad range of durations from 2 to 300 seconds; and performance was compared across different modes of sprinting, namely cycling and running.

“The predictive success of our force application model, both within and across modes of sprint exercise, indicates that as efforts extend from a few seconds to a few minutes, the fractional reliance on anaerobic metabolism progressively impairs whole-body musculoskeletal performance, and does so with a rapid and remarkably consistent time course,” the authors wrote. “In this respect, the sprint portion of the performance-duration curve predominantly represents, not a limit on the rates of energy re-supply, but the progressive impairment of skeletal muscle force production that results from a reliance on anaerobic metabolism to fuel intense, sequential contractions.”

Conclusion of study departs from prevailing physiological paradigm
Since the muscular engines of humans and other animals are similar in terms of their metabolic and mechanical function, the findings likely apply to the burst performance capabilities of vertebrate animals in general, say the researchers.

Bundle is an assistant professor of biomechanics at the University of Montana. Weyand is an associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development at SMU in Dallas.

Funding for the study came from the U.S. Army Medical Research and Materiel Command and the Telemedicine and Advanced Technology Research Center.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Scientific American: Does Double Amputee Oscar Pistorius’s Prosthetic Legs Disqualify Him from the Olympics?

Scientists debate whether prosthetic legs give Pistorius an unfair advantage in the 400-meter race

Scientific American has written a comprehensive piece on the long-running global controversy surrounding double-amputee South African runner Oscar Pistorius, the first amputee to compete in the Olympics.

The July 24 article “Should Oscar Pistorius’s Prosthetic Legs Disqualify Him from the Olympics?” quotes SMU’s Peter Weyand, an expert in human locomotion.

Controversy has swirled around Pistorius as the debate continues over the scientific advantage he enjoys as a result of his high-tech, carbon fiber artificial legs. Weyand helped lead a team of scientists who are experts in biomechanics and physiology in conducting experiments on Pistorius and the mechanics of his racing ability.

Weyand is widely quoted in the press for his expertise on human speed. He is an SMU associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development.

Read the full story.

EXCERPT:

By Rose Eveleth
Scientific American

Runners who’ve faced off against Oscar Pistorius say they know when the South African is closing in on them from behind. They hear a distinctive clicking noise growing louder, like a pair of scissors slicing through the air—the sound of Pistorius’s Flex-Foot Cheetah prosthetic legs.

It’s those long, J-shaped, carbon-fiber lower legs—and the world-class race times that come with them—that have some people asking an unpopular question: Does Pistorius, the man who has overcome so much to be the first double amputee to run at an Olympic level, have an unfair advantage? Scientists are becoming entwined in a debate over whether Pistorius should be allowed to compete in the 2012 London Games.

Pistorius was born without fibulas, one of the two long bones in the lower leg. He was unable to walk as a baby, and at 11 months old both of his legs were amputated below the knee. But the growing child didn’t let his disability slow him down. At age 12 he was playing rugby with the other boys, and in 2005, at age 18, he ran the 400-meter race in 47.34 seconds at the South African Championships, sixth best. Now 25, the man nicknamed the “Blade Runner” has qualified for the 2012 Summer Olympics in London, just three weeks before the games were to begin. But should he be allowed to compete?

The question seems preposterous. How could someone without lower legs possibly have an advantage over athletes with natural legs? The debate took a scientific turn in 2007 when a German team reported that Pistorius used 25 percent less energy than natural runners. The conclusion was tied to the unusual prosthetic made by an Icelandic company called Össur. The Flex-Foot Cheetah has become the go-to running prosthetic for Paralympic (and, potentially Olympic) athletes. “When the user is running, the prosthesis’s J curve is compressed at impact, storing energy and absorbing high levels of stress that would otherwise be absorbed by a runner’s ankle, knee, hip and lower back,” explains Hilmar Janusson, executive vice president of research and development at Össur. The Cheetah’s carbon-fiber layers then rebound off the ground in response to the runner’s strides.

After the German report was released, the International Association of Athletics Federations (IAAF) banned Pistorius from competing. Pistorius hired Jeffrey Kessler, a high-powered lawyer who’s represented athletes from the National Basketball Association and National Football League. It soon became clear that the IAAF’s study was very poorly designed, so when Pistorius’s team asked for a new study they got it. Soon scientists gathered at Rice University to figure out just what was going on with Pistorius’s body.

The scientific team included Peter Weyand, a physiologist at Southern Methodist University who had the treadmills needed to measure the forces involved in sprinting. Rodger Kram, at the University of Colorado at Boulder, was a track and field fan who studied biomechanics. Hugh Herr, a double amputee himself, was a renowned biophysicist. The trio, and other experts, measured Pistorius’s oxygen consumption, his leg movements, the forces he exerted on the ground and his endurance. They also looked at leg-repositioning time—the amount of time it takes Pistorius to swing his leg from the back to the front. (…)

Read the full story.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Discovery News: How Olympic ‘Blade Runner’ Sprints Without Feet

Oscar Pistorius will be the first amputee to compete in the Olympics. Here’s a look at the mechanics of how he runs.

Discovery News has written a comprehensive piece on the running mechanics of double-amputee South African sprinter Oscar Pistorius, the first amputee to compete in the Olympics.

The July 20 article “How Olympic ‘Blade Runner’ Sprints Without Feet” quotes SMU’s Peter Weyand, an expert in human locomotion.

Controversy has swirled around Pistorius as the debate continues over the scientific advantage he enjoys as a result of his high-tech, carbon fiber artificial legs. Weyand helped lead a team of scientists who are experts in biomechanics and physiology in conducting experiments on Pistorius and the mechanics of his racing ability.

Weyand is widely quoted in the press for his expertise on human speed. He is an SMU associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development.

Read the full story.

EXCERPT:

By Sheila Eldred
Discovery News

When the start gun goes off for the individual 400 and 4X400 relay at the 2012 London Olympics, double-amputee sprinter Oscar Pistorius, the man known as the Blade Runner, will spring out of the blocks with the world’s best able-bodied athletes. It marks the first time an amputee will compete in the Olympics.

Pistorius will be wearing carbon-fiber prosthetics designed for sprinting. While the debate over whether his flex-foot Cheetahs makes it harder or easier for him to sprint continues, there’s no doubt that the way his body covers 400 meters is different from his competitors.

As the athletes explode from their starting blocks, the South African born without fibulas will likely get a slower start. Because he can’t flex an ankle or stiffen a leg, it takes slightly longer for Pistorius to start. As the athletes gain an upright position, however, Pistorius will be able to reposition his legs much more quickly than his competitors. It’s that repositioning speed that’s been the point of contention of much of the debate.

In 2008, the International Association of Athletics Federations, track and field’s governing body, banned Pistorius from competing against able-bodied competitors, deeming his blades an advantage.

Pistorius went to Rice University in Houston for what he hoped would be definitive testing that would prove he had no advantage. And at first, that appeared to be the case: using some of the data from the research, published in the Journal of Applied Physiology, the Court of Arbitration for Sport overturned the ban.

But later, two of the scientists pointed to key findings — the repositioning data — that they believe make up at least a 7-second difference in the 400-meter dash. Researchers Peter Weyand, an exercise physiologist at Southern Methodist University, and Matt Bundle, an assistant professor at the University of Montana, presented their case in a point-counterpoint article in the Journal of Applied Physiology in 2009.

The reason the data is so telling, says Weyand, is not just that it shows an advantage; it’s that the comparison between Pistorius and able-bodied world class sprinters is off the charts. (Weyand and Bundle released a statement that explains their science, hoping to clear up misconceptions.)

“With the most generous assumptions, he still comes out seven seconds ahead in the 400,” Weyand said. “He’s a below-average high school runner without those limbs. A lot of people don’t want to hear that.” (…)

Read the full story.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Science: Live Chat — Science at the Olympics

Live Chat: Science at the Olympics

Science magazine hosted a live chat with scientific experts about any competitive advantage provided by the cutting-edge, light-weight prosthetic legs of double-amputee South African runner Oscar Pistorius, the first amputee to compete in the Olympics.

The July 18 chat “Science at the Olympics” included SMU’s Peter Weyand, an expert in human locomotion.

Controversy has swirled around Pistorius as the debate continues over the scientific advantage he enjoys as a result of his high-tech, carbon fiber artificial legs. Weyand helped lead a team of scientists who are experts in biomechanics and physiology in conducting experiments on Pistorius and the mechanics of his racing ability.

Weyand is widely quoted in the press for his expertise on human speed. He is an SMU associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development.

Read the replay.

EXCERPT:

By Nicholas St. Fleur
Science

Every Olympic season brings new scientific innovations that help athletes earn the gold and break world records. This year’s London Games, for example, will see South African double-amputee runner Oscar Pistorius make his debut on the 400-meter-dash while donning cutting edge, lightweight prosthetics. At the same time, Olympic officials will be cracking down on another innovation: new drugs that help athletes outcompete their rivals. Do prosthetic limbs offer an unfair advantage? What is being done to keep steroids and blood doping out of the games? And has scientific innovation become as important a player in the Olympics as the athletes themselves?

Hello everyone and welcome to ScienceLive! As you know, the Olympics are just a week away, and today we’re discussing the role of science in the London Olympics from blood dopers to the ‘Blade Runner’ and whether scientific innovation has become as important a player in the games as the athletes themselves.

Fleur: With us today is Don Catlin, a sports drug expert and professor emeritus at UCLA who founded the UCLA Olympic sport testing laboratory which is a national testing site for performance enhancing drugs in athletes.

To comment on the use of prosthetics in this year’s games is Peter Weyand, an Associate Professor of Applied Physiology and Biomechanics at Southern Methodist University in Dallas, Texas, who has studied the mechanics, physiology and locomotor performance behind running for decades.

Also on the biomechanics scene is J.L. McNitt-Gray, a Professor in the Departments of Biological Sciences and Biomedical Engineering at the University of Southern California, who studies the dynamics of human movement.

Let’s begin with a question for Peter and J.L. South African 400-meter-dash runner Oscar Pistorius will become the first amputee to compete against able-bodied athletes. What allows his prosthetic to help him keep up with the other athletes?

Weyand: Modern lower limb prostheses, in many respects, mimic the mechanical function of a biological leg during running. Two properties of the prostheses are particularly important: weight and springiness.

Excellent data is available to show that for single leg amputees, these limbs almost restore normal function, for double lower limb amputees, they enhance it due to the proerties above.

Single leg amputees are limited by their biological legs. Double limb amputees can fully exploit the mechanical properties of the prostheses for sprint running performance.

Weyand was asked whether the competitive advantage might prompt athletes to voluntarily have their legs amputated in order to have prosthetics.

Weyand: How realistic a voluntary amputation scenario might be is difficult to project at this time. One limitedly recognized aspect of the Pistorius controversy is that reaping the competitve advantages of lower limb prostheses requires having and using two of them. The primary reason Oscar Pistorius is so much faster than other amputees who use the same blades is because double lower limb amputees are quite rare.

Weyand was asked about the need for standardized prosthetics for the Olympics:

Weyand: The standardization issue is a critical one that raises difficult questions for the governing bodies of sport that are not unlike the performance enhancing drug issues in some ways. As science and technology progress, more and more powerful the avenues of performance enhancement become available and the lines between “natural” and unenhanced vs. enhanced become increasingly blurred.

Reasonable guidelines might be possible for prostheses, but the task of evaluating competitive fairness would be resource-intensive and probably never perfect. (…)

Read the replay.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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The London Telegraph: Runner’s world: Usain Bolt and his entourage

The London Telegraph has written a comprehensive piece on Usain Bolt, the fastest sprinter on earth, as he is preparing for the London 2012 Olympic Games this summer.

The April 27 article, “Runner’s world: Usain Bolt and his entourage,” quotes SMU’s Peter Weyand, an expert in human locomotion.

Weyand is widely quoted in the press for his expertise on human speed. He is an SMU associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development.

Read the full story.

EXCERPT:

By Mark Bailey
The Telegraph

The fastest man on earth is lying motionless on the spongy blue running track at the University of the West Indies in Kingston, Jamaica. He appears to be asleep. The elongated limbs of his 6ft 5in body stretch across the track like felled branches. Protruding from beneath his hitched-up T-shirt, a xylophone of abdominal muscles glistens in the midday sun. From a nearby festival the mellow patter of reggae floats along the warm Caribbean breeze. A contented smile melts across Usain Bolt’s face.

This supine figure is surrounded by people in a hurry. A film crew, sponsors and PRs are scuttling around, planning, chattering. A photographer is preparing for his next shot, and wants Bolt in a horizontal position. Unbeknown to anyone, some teenage boys have clambered over a fence and are hiding behind an advertising banner. At intervals they pick up the banner and stealthily shuffle closer to their idol, like cartoon spies tiptoeing behind a cardboard bush. …

… Research by Ethan Siegel, an American theoretical astrophysicist, suggests that Bolt represents a physiological leap forward. The men’s 100m world record has dropped by 0.05 seconds every 10 years since 1968 (when Jim Hines became the first man to break 10 seconds). But Bolt has been performing at a level three decades beyond what should be achievable in the present era, according to Siegel’s graphs. And Dr Peter Weyand, a leading physiologist at Southern Methodist University in Dallas and an expert on the science of sprinting, says “Bolt is a freak – he defies the laws of biology.”

Bolt is blessed with unique physical gifts. “He is such an unusual physical specimen and one need not look beyond that for an explanation of his speed,” Mark Denny, a Stanford University biology professor, tells me. With his long legs, Bolt takes 41 steps to complete the 100m. His rivals take 44. He has a high percentage of fast-twitch muscle fibres, which produce explosive speed, and he can channel more than 1,000lb of force through each stride – double the human norm, according to Dr Weyand. Professor Alan Nevill, a biostatistician at the University of Wolverhampton, suggests his superior height enables him to dissipate heat faster, so his muscles can work harder. …

Read the full story.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.