Thursday, July 28, 2011

running science: sprinters v long-distance runners

i wanted to post a comment regarding a recent article on running science. it's a case study trying to explain why Usain Bolt is such a fast sprinter. those of you on facebook have probably already seen me post it.

i've noticed some people involved in distance running have already started to reference it for insights to improve performance. i, however, wanted to issue a caution on this. i think there are some important details that need to be recognized before anyone attempts to translate the article's points to distance running.

you can reference the article here (the full text of the article is at the end of this post):
a general school of thought (not mentioned in the article) in the track & field community is that 100m sprinters can't afford to be too tall, with the reasoning that taller (and hence more massive) sprinters find it harder to accelerate and harder to generate stride turnover. for a race as short as 100m, both acceleration and maximum speed are important. the belief is that ideal male 100m athletes are around 5 feet 10 inches to 6 feet tall. Usain Bolt breaks this perception at 6 feet 5 inches.

the article explains that sports science shows the role of an additional variable apart from acceleration and stride turnover. according to sports science, elite sprinters, including Usain Bolt, tend to all reach the same maximum possible stride turnover. the article also explains that Usain Bolt possesses the explosive strength necessary to hold an acceleration rate comparable to smaller sprinters. given the parity between Usain Bolt and other sprinters in acceleration and stride turnover, sports science finds that Bolt's advantage is in his capacity to apply more force in less time relative to other competitors. by doing both, he is able to cover more distance per stride and use less strides over 100m/200m relative to other sprinters. other factors being essentially equal, this allows him to be faster.

essentially, the sports science shows that there is an underlying math beneath the acceleration and velocity equation. the typical track & field school of thought conceptualizes sprinting in terms of acceleration and maximum velocity based on stride length and stride turnover, and hence sees running as a function of units of distance and time.

the sports science, however, points to variables underlying these facts: force and force per unit time. these are variables familiar to athletes in other sports like cycling, where there tends to be a obsession with power generation in units of watts.

my caveat is that this approach to running science is not the same for sprinters and distance runners. while useful for sprinting, there needs to be some caution translating it to distance running. i think there is another perspective involving other underlying variables that need to be recognized: energy and energy efficiency.

for sprint running, energy is relevant only to the extent that an athlete can apply more of it in less time. given that the sprinters lining up for a given race all have comparable reserves of energy, the issue is to expend as much energy into running in as little time as possible. this means that for sprinters (especially in the penultimate championship round, when they're going for the gold medal, records, and glory without regard for having to race again later) there is little concern for how much energy is utilized--in fact, the more energy is consumed the better (i.e., for the championship round, it's time to leave everything on the track).

for distance running, particularly endurance running, the situation is different. each athlete starts a race with a finite amount of energy. this reserve depends on the athlete and to a degree can be supplemented by race nutrition. given the distances involved, however, there is an issue of how much energy there is available to complete the race. as a result, there is a greater concern relative to sprinters for how much energy is being expended and at what rate it is being utilized (i.e., the energy reserve needs to last all the way through the race).

of course, a race is a race, and so the goal is always to go as fast as possible to complete a given distance in as little time as possible. but the difference is that in sprinting a given athlete is going to use energy at a higher rate, while in distance running that same athlete is going to need to use energy at a lower rate.

this factors in because the application of force and force per unit time, and hence stride length and stride turnover, requires energy. the greater the stride length or stride turnover, the greater the need for more force or force per unit time, the greater the need to use energy.

for sprinters, given that they all tend to reach the same maximum stride turnover rate, the paramount concern is for accelerating and maximum velocity, meaning reaching and maintaining maximum stride length. energy, at least in terms of consumption rate, is not really a constraint. if anything, a sprinter wants to use energy as fast as possible and ends up using energy as fast as possible.

for distance runners, it's risky to be so profligate with energy. as a result, the concern is not about acceleration and maximum velocity, but rather to find and sustain an optimum stride length that enables the athlete to finish a race in as little time as possible based on the athlete's given energy reserves. relative to a sprinter, a distance runner wants to adjust stride length and stride turnover rate to make energy last longer. in other words: it's less about the maximum, but about an optimum.

which is why endurance athletes need to be cautious in applying the sports science in this article. as a distance runner, you can't run like a sprinter. it's risky to emulate the stride mechanics and power consumption sprinting for long-distance running. as much as a race is a race and power is power and energy is energy and force is force and strength is strength, it's still important to be mindful of how they are all applied. the parameters of sprinting call for different priorities and a different application of these variables compared to the parameters of distance running. don't expect to be Usain Bolt if you're trying to run a marathon.

is it useful to understand the running science of Usain Bolt? yes, as a way of understanding running in general. but also understand that he is a gifted athlete who has been highly trained to fit the very specialized demands of very specific races calling for a very specific type of running. and that type of running is different from distance running.

Usain Bolt: Case Study In Science Of Sprinting
Jay Hart
July 26, 2011

One year from now, the 2012 Olympic Games will begin in London, where all eyes will be on the incomparable Usain Bolt -- the Jamaican sprinter who is more than living up to his name.

Since 2008, Bolt has taken a jackhammer to the 100-meter world record, lopping off a whopping .14 seconds. That might not sound like a huge chunk of time until you consider it's twice as much as any other sprinter has shaved off the world record since the advent of electronic scoring.

Logically, one would think that Bolt did so by moving his legs faster than anyone else. Only he didn't.

Speed, as it turns out, may be completely misunderstood.

When Bolt established the current 100-meter world record in the 2009 world championships, running it in 9.58 seconds, he did so by moving his legs at virtually the same pace as his competitors. In fact, if you or I were to compete against Bolt, our legs would turn over at essentially the same rate as his.

This is a theory put forth by academics and track coaches alike who contend that running fast has more to do with the force one applies to the ground than how quickly one can move one's legs.

More than a decade ago, Peter Weyand, a science professor at Southern Methodist University, conducted a study on speed. Comparing athletes to non-athletes, Weyand clocked both test groups as they ran at their top speed. What he found shocked him.

"The amount of time to pick up a leg and put it down is very similar," he says. "It surprised us when we first figured it out."

So if leg turnover is the same, how does one person run faster than another?

Weyand discovered that speed is dependent upon two variables: The force with which one presses against the ground and how long one applies that force.

Think of the legs as springs. The more force they can push against the ground, the further they can propel the body forward, thus maximizing the output of each individual step. In a full sprint, the average person applies about 500 to 600 pounds of force. An Olympic sprinter can apply more than 1,000 pounds.

But force isn't the only factor. How quickly that force is applied factors in as well.

For this, think of bouncing a beach ball versus a super ball. The beach ball is soft and mushy and when bounced on the ground sits for a while before slowly rebounding back into the air. Conversely, a super ball is hard and stiff and when bounced rebounds almost instantaneously -- and at a much faster speed than the beach ball.

The average person's foot is on the ground for about .12 seconds, while an Olympic sprinter's foot is on the ground for just .08 seconds -- a 33-percent difference.

"The amount of time [one's legs are] in the air is .12, regardless if you're fast or slow," Weyand explains. "An elite sprinter gets the aerial time they need with less time on the ground to generate that lift -- or to get back up in the air -- because they can hit harder."

So what makes Bolt faster than even the elite sprinters? And can he run the 100 meters even faster than 9.58 seconds?

Bolt's superiority is often explained by his unique combination of height, strength and acceleration.

At 6-foot-5, Bolt is two inches taller than fellow Jamaican Asafa Powell (pictured together below) and has six inches on American Tyson Gay -- two of his closest challengers. While it takes most elite sprinters 44 strides to complete 100 meters, Bolt does it in 41.

"Would you rather take 44 steps to your car or 41?" asks Dan Pfaff, who coached Canada's Donovan Bailey to the 100-meter gold during the Atlanta Games in 1996.

Pfaff, now working in London to help boost Great Britain's track-and-field hopes for 2012, says Bolt's height gives him a distinct leverage advantage.

"If you're digging a hole in the ground, you have to get a longer lever to pry [out a rock]," he explains. "If you can control those levers and make them work efficiently, it's a huge advantage."

It's Bolt's ability to control the levers that is so unusual for a sprinter his height.

While taller sprinters may be able to reach a higher top-end speed, getting up to that speed isn't as easy. This can be explained physiologically -- smaller people can exert more force in relation to how much they weigh -- but Weyand prefers a more simple visual to show this to be true.

"You can easily imagine a 4-foot-10 gymnast doing a triple back flip, but imagine Shaquille O'Neal or Yao Ming doing it," he says. "You know they can't do it."

Bolt, it seems, is the exception to this rule. Though he's not doing triple back flips, he does get up to speed nearly as quickly as his more diminutive competitors.

"He has a very unusual combination of being extremely tall and relatively massive and being able to accelerate well. Those things are at odds with each other," explains Dr. Mike Young, a strength and speed coach who trains professionals in track and field and other sports. "He accelerates better than all but one guy in the world -- behind Asafa Powell -- but because he's so massive, he takes fewer strides. If you're that large, once you're moving, you stay moving."

This would help explain why Bolt still managed to break the world record during the Beijing Games in 2008 despite throwing up his arms in celebration some 20 meters before the finish. As Young explains, if the "average athlete is a motorcycle, Usain Bolt is a dump truck," and it takes a lot more resistance to slow down a dump truck than a motorcycle. Thus, when he fatigues, he slows down more slowly.

He has the holy triumvirate," Young contends. "He's one of the top accelerators, has the highest top-end speed and the highest endurance. It's something that's never been seen before. Carl Lewis had the highest top speed, the highest endurance, but he was not the best accelerator."

Bolt, just 24, has set his goal of running the 100 meters in the 9.4 range, explaining to Britain's BBC Radio: "Because that's where I think the record will probably never be beaten."

While Young doesn't think Bolt will break 9.5 in London, Weyand, through his research, says it's possible. Though if Bolt pulls it off, it won't be because he moves his legs any faster.

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