Reading the Sprint Record Book: Wind, Timing and Reaction Time

The 100 metres is the simplest event in athletics to describe and one of the most complicated to record accurately. Over ten seconds or so, the outcome depends on how quickly the athlete reacts to the gun, how fast the athlete accelerates, how well they hold speed, and what the air is doing behind them. The sport has built a set of rules to deal with each of those factors, and understanding them makes the sprint record list much easier to interpret.

Hand timing and electronic timing

Early sprint records were timed by officials using stopwatches. Human timekeepers press the button when they see the finisher cross the line, which means they are always slightly late, and the delay is consistent enough that hand-timed marks are generally faster than the true time by an amount often estimated at a tenth of a second or more. Electronic timing, combined with a photo-finish camera, removed that bias. Fully automatic timing was accepted for the shorter sprint distances in the 1960s and 1970s, and from 1977 the 100 m, 200 m and 400 m world records were recognised only if they were electronically timed. Times are now given to the hundredth of a second.

The practical effect is that the progression of the 100 m record includes a visible break when timing methods changed. A hand-timed mark of 9.9 in the 1960s and an electronically timed 9.9 are not the same speed, and our ranking notes reflect the era each mark belongs to.

The wind rule

A tailwind helps a sprinter by reducing air resistance. To prevent races from becoming a contest of weather, the rules measure wind speed with an anemometer placed beside the track. For the 100 m, the reading is averaged over a ten-second window that begins when the starting gun fires. For the 200 m, a ten-second window is used as well, beginning when the first runner enters the home straight. If the average following wind exceeds 2.0 metres per second, the performance is considered wind-assisted. It can still win the race and still count for results, but it cannot be ratified as a record.

This is the reason you will see lists of "all-time fastest" times that differ from the official record list. There are very fast times that were run with a wind slightly above the limit, and there are others measured on tracks where the wind gauge was disputed. The Florence Griffith Joyner 10.49 for the women's 100 m at the 1988 US Olympic Trials is the classic case. It remains the official women's world record, but the reading from the wind gauge during that race, and the readings in nearby events that day, have been questioned for decades. Our women's 100 m ranking includes the relevant context.

Reaction time and false starts

Blocks fitted with sensors measure the force applied by the athlete. If a sprinter pushes against the blocks sooner than a set threshold after the gun, the start is judged a false start. The threshold is 0.100 seconds. This is based on research indicating that a human cannot reliably respond to the sound of the gun faster than that, so a reaction that quick is assumed to be anticipation rather than response. Since 2010 a single false start disqualifies the athlete, a change that made the start a high-stakes moment, and the rule has been adjusted in various ways since its introduction.

Reaction time is included in the official time, because the clock starts when the gun fires, not when the athlete starts moving. That means two sprinters with the same running time can have different final times if their reactions differ. When the record holder, Usain Bolt, ran 9.58 in Berlin in 2009, his reaction time was about 0.146 seconds, which is not especially quick, and his advantage came from his speed over the rest of the race.

The record holder's pattern

Bolt's progression is instructive. He ran 9.72 in New York in May 2008, 9.69 at the Beijing Olympics in August 2008 (while slowing down and celebrating before the line), and 9.58 at the world championships in Berlin in August 2009. In the 200 m he ran 19.30 in Beijing and then 19.19 in Berlin. The long stride, extraordinary top speed, and the intensity of the competition at those championships are given as the reasons for the performances. Since then no one has run faster, though several have come close, and our men's 100 m ranking shows how narrow the gap is among the fastest.

A short checklist for reading any sprint mark

1. Is it hand-timed or electronic? Marks from before the late 1970s may be hand-timed.
2. What was the wind? Anything above +2.0 m/s is not record-eligible. Negative readings, a headwind, mean the time was set against the wind, and are impressive for the opposite reason.
3. Is it indoor or outdoor? Indoor marks are kept in a separate list, and for a 60 m race, which is run indoors, there is no outdoor equivalent.
4. Is it altitude-affected? Thinner air reduces drag. The rules do not limit altitude for sprints, so a mark from a high-altitude venue is allowed, and we mention it when relevant.
5. Has the mark been verified recently? Check the verification date on the ranking page.

To see how a world record is verified from start to finish, read How a World Record Becomes Official.