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Press Release: Running mechanics, not metabolism, are the key to performance for elite sprinters
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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, http://bit.ly/ODvCrk.
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.
Prevailing physiological paradigms explain both sprint and endurance exercise performance in terms of the availability of metabolic energy. However, for all-out efforts of 60 s or less, the prevailing view is no longer viable. Contemporary evidence indicates that sprinting performance is determined by musculoskeletal force application, with a duration dependency explained by the intrinsically rapid rates at which skeletal muscle fatigues in vivo.
I love these researcher press releases stating that their research is new and exciting and disprove old theories in order to try and create an artificial increase in importance of their research.
I learned that sprinting had nothing to do about metabolic efficiency back in 1978 while a student in Exercise Physiology at the University of California at Davis. That is why we call sprinting an anaerobic exercise....much of the exercise is done using non-oxidative metabolic pathways during a sprint so that the athlete with the most fast-twitch fibers, most muscle power and best mechanics for sprinting will tend to be the best sprinters. Metabolic efficiency hasn't been considered to be important for sprinters for at least 30 years if not longer.....how is this a "classic scientific theory"? Metabolic efficiency is much more important for middle distance and long distance running events.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Re: Running mechanics, not metabolism, are the key to performance for elite sprinters
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But a new study disproves the classic scientific view that conserving energy maximizes performance in a sprinting event.
Wow, classic straw man argument.
Quote:
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.
Wow, they used surface EMG. Maybe they will biopsy muscles from elite sprinters and see if they are different from elite distance runners. Or maybe they will read 30 year old basic physiology textbooks.
Eric
Last edited by efuller : 2nd August 2012 at 09:36 AM.
Reason: double quote
Re: Running mechanics, not metabolism, are the key to performance for elite sprinters
Press Release: THE SCIENCE OF RUNNING: FOLLOW THE BOUNCING BALL
Quote:
Muscle size, genetics and training are among the countless factors that separate Olympic sprinters from the average person. On a fundamental level, however, the mechanics of running are the same for all humans. In fact, they’re basically identical for animals too.
“Science has shown that running is very similar to a bouncing ball,” says Young-Hui Chang, an associate professor who oversees Georgia Tech’s “running lab,” officially called the Comparative Neuromechanics Laboratory. “When humans, horses and even cockroaches run, their center of mass bounces just like a pogo stick.”
This bouncing effect, Chang explains, means that the hip, knee and ankle joints all flex and extend at the same time when the foot hits the ground. Many of the leg muscles are turned on simultaneously, creating force and propelling the runner into the air.
“The greater the force, the greater the speed,” said Chang. “Sprinters and coaches are constantly studying ways to move leg muscles and joints as quickly as possible so that a runner can hit the ground as hard as possible.”
Elite runners and weekend joggers are able to consistently land with the same force, step after step. However, Chang’s research reveals that a stride is just like a fingerprint: no two are exactly alike. The torque generated by each joint is never the same. As a result, your legs have a mind of their own.
“Your knee, for example, automatically adjusts its own torque, each step, based on what the ankle and hip do,” said Chang. “All of this happens without your brain getting directly involved. Your joints ‘talk’ to each other, allowing you to concentrate on other things, like having a conversation or watching for cars.”
By studying how joints adapt to one another, Chang and his team will soon work with amputees to hopefully improve movement for people with prostheses. The researchers are also using their running studies to understand how people walk.
“It may seem backwards to fully understand the nuances of running before we study walking, but walking mechanics are actually more complex. Different muscles are activated at different times in a gait cycle. Joints don’t move in unison. There is no ‘bouncing ball’ phenomenon for walkers.”
Running mechanics, not metabolism, are the key to performance for elite sprinters
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