I suggest that what follows is a fair summary of my involvement in the mid mark chart discussions and the current state of affairs as I perceive them in regard to some facts:
1. The chart was founded on observations made and recorded over many decades. On some occasions physical marks made by vaulters on the runway plus their pole grips (from pole tip to grip) were measured and or estimated. Where precisely the grip was measured - to the top of the uppermost grip or the centre of the grip or the lower (little) finger side of the grip was unspecified. The ground markings used were take-off point and the six-step point out from the back of the box. These appear, so far as I could ascertain, to have been made primarily on an "eyeball" examination of predominantly USA male vaulters to determine the six-step mark. In some cases cinefilm and or video was used to obtain these data. Where measurement was made on the actual runway a tape measure was used. The measurements obtained and measured in this way were associated with 6-inch increments in bar height and drawn up into a chart form by DJ.
2. DJ constructed a chart initially where bar height and associated grips (measured from pole tip to grip), takeoff points (in feet and inches) and the location out from the back of the box of the 6 step out point (in feet and inches) was marked on the chart. These data were obtained from a small (my description) sample of Male American elite vaulters with some observations of other individual international (notably former Soviet Union vaulters, French and other Nationalities) level vaulters. More recently data for female American vaulters have been used. A metric version of his chart was also produced to which average speed (I am unclear how precisely this was measured but understand it as being the average speed from 10m out to 5m out) was added.
3. In order to get DJ to be specific about the chart I put up objectively collected (video and Laser Gun measurements) data from competition and training jumps of one male elite international level vaulter (World Indoor / Outdoor and Olympic Games top six finalist and one female national level calibre vaulter.
The data included stride length, stride rates and average speed per step, on a step by step basis, for the full approach run-up of each vaulter. I requested DJ on the basis of his chart to tell me the grip height and six-step mid marks that the vaulters should have used. Following a request to me to supply grip heights (pole tip to top of grip of the top hand), DJ was close in his estimation of the six step mark of the elite male (DJ suggested that the precision of his estimate was +- 8 inches) ie he was within 16 inches (ie 0.406m) for the male and was out by more than that amount for the female vaulter.
On the basis of this outcome I concluded that the DJ mid mark chart gives a general guideline to where the six-step check mark should be located for a particular grip height but suggested it would need to be honed by the coach and vaulter to match specific cases. I recommended the chart for beginner coaches and vaulters as a useful and sound general guide. Note that I did not trash the chart!
4. Next I tried to establish the precise methodological basis DJ used to calculate his six-step mid mark estimates. To do this I presented actual data obtained from World Championship and Olympic Games finalists for the final four steps of their best vaults in those competitions. Included in the data I supplied were the vaulter's Stature (height), Body Mass, and pole tip to top of the uppermost grip hand length used by the vaulters for whom data were published. The data also included the individual step length, step rate and the average speed of each step, on a step by step basis, for the final 4 steps of the approach run-up. DJ challenged the accuracy of these data. However his challenge I assessed to be an unsubstantiated assertion of his claimed personal knowledge with respect to Earl Bell in particular. The scientific bona-fides of the researchers responsible for the reports were acceptable to the IAAF, and the methods and procedures used were of the highest standards available at the time. I took the data as reported to be valid rather than accept DJ's attempt to negate their validity. DJ put up no evidence to back his claims.
The data I presented showed that vaulter step length and step rate varied on a step by step basis when compared within and between vaulters during the final 4 steps of their approach runs. Also data obtained for the same vaulters in different competitions (World Champs & Olympic games) showed similar outcomes. The data were derived using methods and procedures acceptable to both the IAAF and biomechanists on both occasions. (Note: there were some variations in the cine camera speeds used at the separate competitions but definitions of terms and the data analysis procedures were the same and met the scientific reliability and validity requirements within limitations of the studies).
In summary the important feature of the results relevant to the mid-mark chart discussion (this is my view of the results) is that a vaulter's step length and step rate in the final 4 steps of their approach run, as performed at World Elite Level in competition, varied step by step.
Whilst average speed is the product of step length and step rate, I concluded that average speed taken over 6 or 4 steps is not necessarily a true indication of any actual step length or step rates used by a particular vaulter.
In other words at this elite level it is possible for the same average speed to be achieved due to it being the product of differing combinations of the step length and step rate.
Another way of putting this is to posit that vaulters who are able to travel the same horizontal distance in the same time and thereby achieving the same average speed actually employ a uniquely personal pattern of step length and step rate relationships whilst doing so.
I concluded on this evidence that step length and step rates are not invariants (ie retain the same or constant values) even though vaulters may produce the same average speed during the final 6 steps to travel the same distance in the same time of the approach run in pole vault.
5. There was some discussion on the issue of stature and leg length and the findings reported by Weyand and his group. Stature is a partial determining factor but not the only one that limits the step length of a vaulter. Because resultant ground reaction force at toe-off in each running step is the major determinant of a running step flight time (all other factors being equal - my caveat) the horizontal distance covered is thus primarily determined by flight time. Since step length is defined as the horizontal distance measured from the toe-off point on the ground of one foot to the toe off point of the contralateral foot, foot length also contributes to step length. Clearly foot length which is related to stature contributes to step length but to a much lesser degree than flight time. Note that at no stage in the discussions have I stated or claimed that stature, particularly leg length to be the sole determinant of step length.
6. In response to data that others and myself put up re elite male and female 100m sprinters DJ put up his data for Tim Mack and Sergey Bubka. DJ used the data to show the mathematical method he employed to calculate 6 step average speed, 6 step average step length and step rates. He requested that his mathematics be checked.
I have checked the calculations and don't have any issue to raise as to the correctness of the mathematics procedures (simple addition, division, and multiplication) used. I do however have three issue in regard to the 4.40m take-off distance used to make the 17.06m estimate for Bubka's 6 step check mark.
Firstly, as far as I am aware, Bubka did not use 6 step check marks!
Secondly I have assumed DJ used his chart to obtain the 4.40m take-off point and therefore no check can be made as to the precision or accuracy of the estimate arrived at. Explicit knowledge of the actual take-off distance and the actual 6 step out touch down distance would be required to do this. Neither of these essential distances is given and hence the accuracy of the estimate cannot be substantiated independently. Thirdly without knowing the magnitude of the real life datum values a calculation of an average based on 4 step lengths extrapolated to be indicative of the average for six steps gives us a "ball park" estimate only. There is insufficient information to judge the size of the ballpark and thereby get an indication of the precision of the guess.
7. Whilst these exchanges were taking place Ladyvolscoach put up an intriguing and startling video obtained using Dartfish software processing of digital video images. Statements were made in regard to what the videos showed, particularly regarding timing accuracy, that caused me to try to clarify how the images were obtained, processed and reproduced using the Dartfish system. These enquiries have continued.
Ladyvolscoach needed medical treatment and DJ was offshore in Europe. There the matters stood and then followed DJ's quite extraordinary outburst! I will not enter into that vitriolic clash of the Titans!
8.
dj wrote:by dj on Fri Aug 01, 2008 4:47 pm
hey
one of the things ladyvol showed me with dartfish was how two athletes would have the same frequency but different SIX sTEP MARKS..one longer one shorter.. for example bubka.. 57 feet tim mack 55 feet.. if you didn't know the six step marks you woulld think tim was running as fast as bubka.. but bubka was covering more ground in the same time.. something like 1.37 seconds for the last six steps..
the bottom line was that human potential was very simular in steps per second,, frquency.. on the same surface that is... it was the amount of force that gave the longer stride lengths.. there ground times were also very simular .. again indicatiing it was the force creating the stride length.. tim has a longer inseam than bubka so it wasn't "longer legs.. longer steps.." that is a miss conception..
Finally the quote from DJ's response of Friday August 4th reveals the kernel of the issues that remain to be resolved. They lie at the heart of my attempting to contribute to what I understood to be a public forum discussion.
The first paragraph exposes the confusion DJ has had in regard to the interaction of step length and step frequency that must be considered in comparing vaulters. Vaulters who appear to be moving their legs at the same rate and not necessarily have the same step lengths are according to DJ a concept he had not fully appreciated or understood until Ladyvoscoach helped him see his misunderstanding using Dartfish.
The second paragraph is typical of many of DJ's statements in that it contains grains of truth whilst sometimes making explanatory assertions that are demonstrably questionable on factual and or logical grounds or both. For example " it was the amount of force that gave the longer stride lengths.. there ground times were also very simular .. again indicatiing it was the force creating the stride length.." DJ simply can not know this unless he has actually made the measurements and or can point us to the evidence.
There are elements of truth in much of what DJ asserts but when pressed by us lesser mortals to be specific and to explain his versions of science and the physics he claims underpins his chart he unfortunately demonstrates his exasperation when we fail to understand or agree with him. DJ by resorting to his now infamous tactic of venting his spleen over long held animosities or imagined personal attacks does himself and his mid mark chart a disservice. What a pity!
I thought, quite wrongly, that my input and DJ's responses to them might establish whether the 6 step mid mark chart had the scientific underpinning claimed and the precision to be applied as rigorously to all vaulters in their run up as DJ confidently proclaims. If the chart had the infallibility claimed then I could accept DJ's insistence that to vault correctly all vaulters with the same grip (pole tip length to top of the top hand) should be made to have approach run parameters that match the 6 step mid mark chart. Instead, I will continue to employ a coaching approach in which the approach run is developed according to the realities of the levels of competence, physical capacities and acquired ability of each individual. DJ has failed to convince me to rely solely on his Pole-Vaulter Holy Grail the 6 step Mid Mark Chart. The chart is a useful but not perfect coaching tool. It is, in my view, unreasonable for the DJ chart to be espoused by anyone as the panacea to all vault technical problems associated with the approach run final 6 steps. The evidence is insufficient for such a belief to be credible. The post hoc science based explanations for the claimed efficacy of DJ's chart remain to be substantiated by DJ. Claiming that it all boils down to the "physics" is one thing. For DJ to show how this is the case is quite another! DJ continues to struggle valiantly in this regard. How wrong I was to be so presumptuous as to believe myself able to assist DJ to clarify the "science".
I still remain an avid student of the event but having done what I can to get at the facts and scientific underpinning for the DJ chart I withdraw because discussing / arguing with DJ is to debate founded on quicksand. The risk of character assassination and personal insult is also far too high for me to continue.
I end my contribution to this PVP forum thread with a quote that exactly captures my belief as to claims made for the efficacy of the DJ 6 step Mid Mark Chart.
"There is no absolute knowledge. And those who claim it, whether they are scientists or dogmatists, open the door to tragedy. All information is imperfect. We have to treat it with humility."
Jacob Bronowski, The Ascent of Man. (1973).
