How a sprint start works
In sprint races up to 400 m, the starter’s commands are On your marks and Set, and the athletes start from blocks, as set out in Rule 16 of the World Athletics Technical Rules. The rules don’t fix how long the starter waits between the commands, or between Set and the gun: the gun fires once every athlete is motionless in their set position. That unpredictable hold is what makes a sprint start a test of reaction.
Starting before the gun is a false start. At major championships a start information system reads force sensors in the blocks, and a reaction time under 0.100 s is treated as a possible false start (Rule 16.6): the race is recalled and the starter checks who moved. Except in combined events, the athlete responsible is disqualified (Rule 16.8), with no second chance.
How the test works
Turn your sound on. Click the box, tap it or press Space, and you are on your marks. After a couple of seconds the box says Set. Then, after a random hold of 1.2 to 2.8 seconds, the gun fires: a sharp crack from your speakers or headphones. Nothing on the screen changes, so you react to the sound alone, as in the blocks. Press as fast as you can. Your reaction time appears in seconds, like on a results sheet, with your last ten starts underneath. Going before the gun is a false start, and so is a reaction under 0.100 s.
Reaction times in a championship final
The biomechanics report from the 2009 World Championships in Berlin (Graubner and Nixdorf, New Studies in Athletics, 2011) lists every finalist’s reaction time. The men’s 100 m final, the race of Usain Bolt’s 9.58 world record:
| Athlete | Result | Reaction time |
|---|---|---|
| Usain Bolt (JAM) | 9.58 | 0.146 s |
| Tyson Gay (USA) | 9.71 | 0.144 s |
| Asafa Powell (JAM) | 9.84 | 0.134 s |
| Daniel Bailey (ANT) | 9.93 | 0.129 s |
| Richard Thompson (TRI) | 9.93 | 0.119 s |
| Dwain Chambers (GBR) | 10.00 | 0.123 s |
| Marc Burns (TRI) | 10.00 | 0.165 s |
| Darvis Patton (USA) | 10.34 | 0.149 s |
The fastest reaction didn’t win: Bolt left the blocks sixth of eight and still won by 0.13 s. In the women’s final, reaction times ran from 0.130 to 0.173 s, and the winner, Shelly-Ann Fraser-Pryce, reacted in 0.146 s.
Is 0.100 s the right limit?
The limit assumes that nobody can hear a gun and react in under a tenth of a second. Pain and Hibbs (2007) tested nine athletes in instrumented blocks and found that five of them averaged under 100 ms in at least one test condition, and at the 2022 World Championships in Eugene, Devon Allen was disqualified from the 110 m hurdles final for a reaction of 0.099 s. Timing systems also differ: a 2018 study in PLOS ONE found that the fastest reaction times at the Olympics fell from 2004 to 2016, most likely because the force threshold the blocks use, which isn’t published, was lowered, not because sprinters got quicker.
Reading your time
A press of a key isn’t a push against the blocks, and your device adds delay of its own: the sound needs time to reach your ears, and the page takes out only the part your browser reports (shown under the box after the first start). Bluetooth headphones add more, so use wired headphones or the device’s speakers. Compare your starts with each other, or with friends on the same device, rather than with the table above.
For the same kind of test with a beep and five attempts, see the sound reaction time test. The classic test uses a colour, and the F1 start lights a set of lights.