07 January, 2014

Wind effects

I would like to start this post with a 1980 quote by Bert Nelson, editor of Track and Field News: "The philosophy behind the official approval of sprint records is absurdly primitive. Permitting a record with a tailwind of 2 m/s was an arbitrary decision. Why should 2.01 m/s be illegal and 2.0 m/s be legal?" he argued. 

Given the current legal limit, famous performances could have been invalidated had we had better measurements of wind speed. The forum of Track and Field News hosts extensive discussions on the validity of wind speed measurements at Mexico during the 8.90 m Beamon jump. 




The consensus is that the reported 2.0 m/s wind speed is not accurate and that the real speed was substantially higher. A video of the jump shows a small flag situated next to the reception area undulating under a wind which looks stronger than the measly 7.2 km/h.
The fantastic 10.49 s world record of Florence Griffith-Joyner 



was supposedly registered under a 0.0 m/s wind during a competition where winds of 5 m/s were prevailing. N. Linthorne has published a detailed analysis of this competition where he presents compelling arguments in favour of the existence of a tailwind of more than 5 m/s for the race of Flo-Jo. (If this performance were discarded the current world record would be a quite respectable 10.61 s, still by the same athlete). Another case where the wind measurement played a major role (invalidating a world record) was the 8.96 m jump of Ivan Pedroso in Sestriere. 



While the wind measurement was perfectly legal, at 1.2 m/s, the record was invalidated on the argument that the wind gauge was obstructed by the body of a judge (a decision which, I, personally, deplore). 

To echo the criticisms of B. Nelson, I find the rules concerning the wind speed limit quite arbitrary. The current rules stipulate that “If the wind velocity, measured in the direction of running or jumping, behind the athlete averages more than 2 metres per second, the record will not be accepted”. This restriction is valid for the races of 100 m, 200 m, 110/100m HD and the long and triple jump. It was imposed by the 1936 Berlin Congress of the IAAF, following a german proposal of a speed limit of 1 m/s. The current limit (which is obtained as a mean velocity measured over a given time period, 10 s for 100 m or 5 s for the long jump etc.) is thus just a compromise, without any scientific foundation.  

If the situation for individual events is somewhat awkward that for combined events is downright ridiculous. Until 1964 there was no wind restriction for combined events record homologation. Then in the Tokyo 1964 IAAF Congress the rule for individual events was extended to the combined events as well. To my eyes this is the only logical decision. However, the IAAF, under the pressure of athletes and coaches, amended the rule increasing the wind speed limit for the disciplines of 100 m, 200 m, 110/100m HD and long jump, to 4 m/s. This means that a record of, say, 100 m in the decathlon, registered with a wind speed of more than 2 m/s but less than 4 m/s, can be perfectly valid and better than the standing world record of 100 m. Probably this was motivated by the fact that, raising the speed limit in combined events, the wind assistance rule would apply less often. (In which case, raising it further would cause even fewer problems of wind-related record cancelation, and so on ad absurdum). There was a 1969 proposal by the federation of New Zealand, reported in the 1991 volume of Athletics, to measure the wind speeds over all the concerned events (100/200 m, 110/100 m and long jump in decathlon/heptathlon), average them and require that the average not exceed 2 m/s. While this proposal had the advantage of doing away with the arbitrary value of 4 m/s, it would not prevent the decathlon 100 m record being superior to that of the individual race. Anyhow, the proposal was not accepted and now we are stuck with the 4 m/s absurdity.

And while for 100 m, 200 m, 110/100m HD and the long and triple jump one can understand the necessity of a wind speed limit (although I will devote a future post to the case of the hurdles, which necessitate a special treatment) one can wonder why the remaining track and field events are exempted from the wind assistance rule. An elementary calculation shows that while running against a headwind one loses more than what one gains while running with a tailwind. Thus when there is a wind of non-negligible strength all athletes running 400 m or more are at a disadvantage. And what about discus (and, as a matter of fact, javelin also) where a strong headwind offers a definite advantage? There is no rule whatsoever limiting the validity of records in throws with a strong headwind.

What can be done? To begin with, let us assume that the existing top-quality anemometers can provide almost instantaneous measurements, without delays, sampling wind velocities over very short time intervals. The first step would be to calibrate the stadia under several wind conditions, and complement the extensive measurements by simulations, so as to be able, by using a not excessive number of anemometers to give the value of the wind speed at any point of the stadium over all times. The “any point” requirement is essential since it is clear that the wind speed is not the same over all lanes even in a straight line race. Moreover every stadium has its particularities with “wind shadows” and “wind channels” which may result in quite appreciable differences in wind speeds even between not very distant locations. With the proposed calibration we would be, in principle, able to know the precise value of the wind speed for every athlete at every instant of his/her effort.

And now comes my proposal. Since any value of wind speed limit is arbitrary there is only one solution: 0 m/s, i.e. no wind at all. In fact the initial proposal is that of B. Nelson who in 1979, suggested that the registered sprint times should be adjusted so as to take into account the assistance of the wind. Today, 35 years later, this proposal appears quite realistic. The recent progress in biomechanics would allow the elaboration of quite realistic models which could estimate the corrections to be applied to performances in the presence of wind (be it tail- or headwind) so as to evaluate the equivalent performances at “zero wind”. The IAAF could establish a working group with the aim of building the most elaborate model for the estimation of the wind effect or perhaps organise a symposium around this same theme and select the most satisfactory model for the wind-due corrections. These wind corrections should be applied to all track and field events. Moreover the model should provide for corrections due to altitude (all performances should be adjusted to sea-level ones; an unfavourable choice) and latitude. For the latter, the simplest solution would be to adjust the performances so as to bring them to the equator (a choice favourable for the athlete).

What is the probability of acceptance of a proposal to adjust the performances for zero wind speed? Unfortunately, exactly equal to the proposed wind speed.

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