Wind Assistance

Introduction   Wind Assistance   Accuracy   Flojo's 100m World Record

Introduction

My interest in the effect of wind in athletics began when I moved to Perth, Western Australia for my PhD studies.  Perth has a famous afternoon seabreeze called the 'Fremantle Doctor' which always blows in the summertime (because of heating of inland areas.)  This breeze has a strong influence on sports in Perth (eg. sailboarding is very popular).  In athletics, the breeze is particularly troublesome because the layout of Perry Lakes stadium means that sprinters always run directly into the wind.  It is very difficult for sprinters to record a fast time and qualify for the National Championships.  On the plus side, Perth is a 'mecca' for pole vaulters.  The strong and reliable tailwind makes for a great training environment and an excellent venue for competition.

Wind Assistance in 100m Sprint

It is well known that sprinters run faster with a tailwind and slower with a headwind.  I was interested in how you go about converting wind-assisted or wind-hindered performances into equivalent performances with no wind.  Several theoretical studies have been conducted, but they have some doubtful assumptions which result in differing conclusions.  A definitive experimental study was needed to settle the matter.

I conducted a study of the effect of wind on 100m sprinters using competition performances published in athletics magazines.  (For this experimental study, the data already existed!)  The study showed that the advantage of a 2.0 m/s tailwind (the legal limit for recognition of records) is about 0.10 seconds.  Also, the disadvantage of a headwind was found to be greater than the advantage of a tailwind of the same magnitude.  (This effect is well known to middle and long distance runners.  These athletes have to run laps of the track and so they prefer still conditions if they are aiming to run a fast time.)  A wind correction curve was produced, and this has been adopted by the athletics community.  (See, for example, "The Little Green Book" published by Track & Field News.)

To find out more about the wind assistance study, see:

Linthorne N.P. "The effect of wind on 100-m sprint times" Journal of Applied Biomechanics 10 (2) 110-131 (1994).

Linthorne N.P. "Wind assistance in the 100-m sprint" Track Technique 127 4049-4051 (1994). (PDF)

Accuracy of Wind Readings

In the sprint events, races are timed to the nearest 0.01 seconds and the official wind reading is a 10 second measurement obtained from a single wind gauge placed next to the track.  My wind assistance study indicated that if athletes are to be treated fairly when recognising world records the official wind reading must be accurate to ±0.2 m/s.  It has long been suspected that the official wind reading does not always provide an accurate representation of the wind affecting the athlete as they run down the track.  A study of wind conditions at the Sydney Athletic Centre showed that the accuracy of the official wind reading is only about ±0.9 m/s.  This is equivalent to an accuracy in race time of about 0.05 seconds.  Therefore, the occasional injustice may arise in the recognition of world records.  The accuracy of the official wind reading could be improved to the required level by using several wind gauges placed along both sides of the 100m straight.  An instantaneous wind measurement would be taken as the runners passed by each wind gauge.  However, this approach would greatly increase the cost and complexity of organising an event that meets the requirements for consideration of world records.

Thanks to Masaki Wakai, Tom Reddin, Deena Rosalky, and Hassan Chalich for helping out with this study.

To find out more about the wind accuracy study, see:

Linthorne N.P. "Accuracy of wind measurements in athletics" in "The Engineering of Sport: Research Development and Innovation, Proceedings of the 3rd International Conference on The Engineering of Sport, Sydney, 10-12 June 2000", A.J. Subic and S.J. Haake (Editors), Blackwell Science, Oxford 2000 pp. 451-458. (PDF)

Flojo's 100m World Record (10.49 sec)

An unexpected outcome of the work on wind assistance was the discovery that Florence Griffith-Joyners' 100m world record was an illegal (wind-assisted) performance.  Flojo recorded 10.49 seconds in the quarterfinals at the 1988 US Olympic Trials.  This performance broke the existing world record by 0.27 seconds, and no other sprinter has come anywhere near the mark since. However, the official wind reading was considered 'highly suspect' by those who witnessed the race.  The September 1988 issue of Track & Field News had a column titled "Everyone Knows it's Windy", which included the comment: "It's hard to say which number caused the bigger gasp at the Trials, Florence Griffith Joyners' 10.49 at the finish-line time indicator, or the 0.0 which popped up on the mid-straight wind board".

The doubts about the official wind reading (0.0) were confirmed by my study of the 100m races at the Trials.   Plots of race time versus wind reading were examined for deviations from the expected relation.  The wind reading for Flojo's 10.49 race was clearly anomalous.  For all competitors in this race (not just Flojo), the race time indicated that the wind reading should have been between +5.0 and +7.0 m/s.  The 10.49 performance was definitely wind-assisted.  The real world record should be the 10.61 performance that Flojo set in the final at the 1988 US Olympic Trials.

Unfortunately, the IAAF has not yet corrected the world record list.  The April 1994 issue of Track & Field News had a column in support of the findings, and since 1997 the International Athletics Annual of the Association of Track and Field Statisticians has listed Florence Griffith-Joyner's 10.49 performance as "probably strongly wind assisted, but recognised as a world record".  In the 2003 edition of  IAAF World Records, Richard Hymans concludes "this is a world record which should not have been ratified".

Note: Many of those involved in running the 1988 US Olympic Trials were opposed to the 10.49 performance being submitted to the IAAF.  However, the relevant paperwork was signed and the performance was ratified as a world record.  It seems that common sense 'took a holiday' at this track meet.

To find out more about Flojo's 100-m world record, see:

Linthorne N.P. "Was Flojo's 100-m world record wind-assisted?" Track Technique 127 4052-4053; 4057 (1994). (PDF)

Linthorne N.P. "The 100-m world record by Florence Griffith-Joyner at the 1988 US Olympic Trials" Report for the International Amateur Athletic Federation, June 1995. (62 pages) (PDF)