Friday with the Docs, Dr. Yessis Takes a Deeper Look into Weyand’s Research

 

Usain Bolt

 

In today’s friday with the Doc’s Dr. Yessis examines Dr. Weyand’s research and brings about two great questions: Where does the vertical force go, and how does it move us forward?

Have the right conclusions been drawn regarding Usain Bolt?

Over the last few weeks much attention has been given to analysis of the world class runs by Usain Bolt. In recent articles that appeared in the New York Times, Post Game and other outlets on the web, Dr. Peter Weyand is quoted as being the de facto running expert. In his interview his reasons for Bolt’s success were brought out. His study of sprinters and his analysis of why Bolt was successful, however, leave much to be desired. His comment that “the scientific understanding of sprinting is pretty immature “ indicates that he does not truly understand what is involved in sprinting.

Thus to determine if he is truly the de facto running expert it is necessary to closely examine his research findings and especially his conclusions. In addition, it is necessary to look at how his results are being interpreted by the running community. For example:
1. In Weyand’s research he compared athletes to non-athletes to find differences in their running. This should automatically raise a red flag because the differences between these two levels of runners are too great and extreme. Much more valid and practical would have been a comparison between elite runners and the next level of runners as for example, runners who are capable of running the 100 m in 10-10.5 seconds or even those who run the 100m in 10.5 to 11.5 seconds. Such studies would be more indicative of what makes the elite runner superior.

2. Regardless of this, other aspects of his findings can also be questioned. His findings that the force with which one presses against the ground

Sprinting Vectors

and how long one applies that force is not being disputed. These are legitimate findings that show a major difference between athletes and non-athletes. However, these differences have been noted for at least the last 30 years. What was not addressed by Weyand, is an explanation of what these differences mean or how they are produced. This would have added knowledge to the field.

For example, the elite runner produces over 1000 pounds of vertical force on contact with the ground. More important for coaches and practitioners to know is how the force is produced and what happens to this force after it is produced on contact in the support phase. How much of this force is given back and in what direction is the force given back?
He does not address these factors but yet it any good research the researcher must be able to explain how and why he arrived at the results that he found. If he cannot explain the how’s and why’s of the results then he must go back to the drawing board to determine these answers or even if the results can be reproduced with different subjects

3. He draws conclusions that are not substantiated. By only emphasizing the vertical force produced on touchdown in a very short time it has led coaches to believe they must produce a vertical force in the return pushoff. This however, is erroneous without knowing what happens to the forces after they are produced and how much vertical force is actually produced at the moment of toe off.

4. In physics it is known that in order to move in a horizontal direction the force applied to the ground must be applied in a horizontal manner. Since it is a vector force this means that the force must also have direction. But this is not mentioned and the reader is left with the impression that the only thing that matters is the creation of vertical force on the landing and to be sure that it is a maximal force. As mentioned earlier, how this force is produced or what happens to this force during support is not mentioned. Good or valid research, as everyone should know, is based on facts not assumptions. All recommendations must be based on fact!

5. There are still other aspects of the research that can be questioned especially since they were not discussed in his research. For example, it was brought out that Bolt moves his legs at “virtually” the same pace as his competitors. ”Our legs would turn over at “essentially” the same rate as Bolt’s.” But does virtually and essentially mean that these rates are statistically significant and if so, at what level of significance? When the difference between winning and losing among elite runners is in the thousandths of a second, knowing this becomes extremely important. Differences with non-athletes however, are for the most part, immaterial.

6. The most glaring finding that appears to have been overlooked is that Bolt took only 41 strides in comparison to other elite runners who took 44 strides. This contradicts his conclusion that runners move their legs at the same speed while airborne. Having the same airborne speed does not mean that leg speed is the same in different level runners. Because Bolt took 41 strides it means that he covered more ground in one stride than the other runners. In other words, the distance that the legs traveled was greater. If airtime is the same it can only mean that the legs traveled faster to cover the greater distance in the same amount of time. This is basic physics.

From my experiences in working with many sprinters, it is the force and speed that he generates in his forward knee drive and paw back that is the major part of his speed. This is where over 80% of the energy is expended in sprinting to drive him forward. But these facts are left out and everyone is led to make assumptions and use examples that only tangentially apply. Looking at the energy expended would enable us to better understand how Bolt is capable of maintaining his technique – and resultant speed – throughout the entire 100 m.

7. The biggest problem based on the comments made by Weyand is his lack of describing or perhaps more accurately, understanding of what takes place in running. The findings in all good research must be explained! To do this it is necessary to examine running form (technique). But this is sorely lacking. In fact, from what I have been able to determine he believes that technique is not important. But, a good researcher must be able to equate the force that is produced with what is happening in the running stride in order to fully comprehend what is taking place.

The only important factor brought out is that maximal force must be produced on touchdown in the shortest amount of time. But why they are most important and why technique is not important is not addressed except superficially in the comments and statements made by Weyand and his supporters.

8. Other coaches quoted in this article that is currently circulating around the web, also have muddled our understanding of running with some of their comments. For example, according to Dan Pfaff who coached Donovan Bailey, gold-medal winner in the Atlanta Games, Bolt had a greater ability “…to control his (leg) levers that is so unusual for a sprinter his height”. An illustration is given by Weyand of a short and tall athlete doing back flips to indicate speed of rotation. Rather than showing only that short-leg levers allow the athlete to rotate faster, he omits the fact that the longer leg lever can create greater force. This is known as the law of conservation of angular momentum. Thus is it really control of the levers or his ability to quickly and forcefully accelerate the levers of his legs? Study of his technique show this but it is ignored.

9. Another misconception perpetuated can be found in the statement that “smaller people can exert more force in relation to have much they weigh”. This holds true only with people who weigh the same amount. A taller person who weighs more can produce greater force. In addition, it is necessary to look at what kind of strength training was done and how strong each individual is, especially when looking at the main muscles involved in the running stride. This however, is ignored.

10. It is the force and speed that Bolt generates in his forward knee drive and pawback that is critical to his speed. The faster these actions are executed and the longer the leg lever, the greater can be the force produced on touchdown. These actions take over 80% of the energy expended in sprinting to drive him forward. But these facts were left out and everyone is led to make assumptions and use examples that only tangentially apply. Looking at the energy expended would enable us to better understand how Bolt is capable of maintaining his technique – and resultant speed – throughout the entire 100 m.

Explosive Running

Thus rather than stating that Weyand is the de facto running expert we should insist on more details from him and others to explain what takes place during the running stride. Keep in mind that he only brought out two findings that were already known. But his erroneous conclusions have been spread in the popular press which has led to greater confusion in the field and to many erroneous and detrimental practices. Instead of providing greater clarity and giving coaches solid information that they can use to improve their athletes performance, he has done just the opposite. We should be more demanding of our researchers.

For more information on running technique and the role played by the limbs in each phase of the stride see the second edition of Explosive Running

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Comments

  1. From the article above:

    “This however, is erroneous without knowing what happens to the forces after they are produced and how much vertical force is actually produced at the moment of toe off.”

    High speed t-mill data clearly indicates how much vertical force is produced at toe off–virtually none.

    The following SMU analysis makes it clear. Check out

    http://www.youtube.com/watch?feature=player_profilepage&v=RH8JYunGhWs

  2. A further analysis of the pawback and pushoff relative to a contributor to force on the ground can be found at:

    http://www.youtube.com/watch?v=GarhSbmbraI

    • Jay DeMayo Jay DeMayo says:

      Ken,
      First, thank you for the post along with the videos attached with them, they are truly appreciated. I would, however, like to touch upon a few statements used in the videos and ask a few questions about the means where your observations were received. The first of which would be the use of the treadmill. Although I do understand that for research purposes one must use the treadmill because there would be no feasible way of utilizing a force plate through an entire distance covered, my concern is that in using a treadmill there is minimal need for any force to be produced at toe off because you are not actually displacing the center of mass at all, but rather just moving your legs fast enough to keep up with the treadmill. Without having to move you forward, there is no need for a forceful push off. This is why running on a tread mill has been referred to as performing “hundreds of leg extensions” by certain individuals in the industry.
      I am also interested in discussing your statement that “runners at steady speed have no need for propulsion.” You stated earlier that all vertical forces were dissipated. If no force is being produced, how does one continue to stay at the same speed with gravity pulling the individual down, resistance of the air, the static coefficient of friction of the ground vs. the footwear of the athlete and energy substrate utilized during said movements? With all that is involved in deciphering how we move forward, wouldn’t one have to produce force to move the body forward, not just “rotate over the plant leg”? If all we do is rotate over the plant leg and we do not have to exert force at either toe off, nor pawing back to develop speed back to the ground, how then do we increase acceleration and top end speed? Since speed has been defined as being the product of stride length and stride frequency, if we do not improve one or the other then we would never see improvements in speed, correct?
      Now, I do understand that Newton’s Laws state that once an object is in motion it stays in motion, but the outside forces here would slow the individual. One could infer, based on your statements, that once you reach top end speed, you can hold it for as long as needed, but we know this is not the case.
      I know this isn’t the most scientific of answers, but a prime example was shown on Sports Center just the other day. They showed the fastest players in the NFL and had them running in a game with the miles per hour (speed) listed below them as they ran on screen. Never did the speed remain constant while they were in the open field. Now, again, I realize this is not an “academic” response, but one could derive from this that this should be examined if your statements are truly factual. If speeds change from stance to push off, and differ depending on the leg that is landing on the ground, then couldn’t it be said that this is based off the individual’s ability to pull their leg back to the ground and push them forward?
      The final question would be in regards to improving performance. If there is no paw back and no push off, how do we make people faster? On top of that, if all forces are dissipated, what is the point of strength training? Is it just to dissipate forces more efficiently? Does this efficiency increase the individual’s ability to move at a faster rate? If that matters, where does the speed come from then? If there is no pawing action to “pull” the leg back and then no “pushing” action at toe off, than how do we move since all the force is dissipated?
      I do realize that with force plates there may be a limit to analyzing the horizontal forces provided, or the direction of forces, but surely, if there is any force where the leg is not directly under the body then using mathematical equations we should be able to find what the horizontal forces are and the angular forces that make up the hypotenuse of the triangle, correct?

      Thank you again for your post.

      J

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