Starting Gun: Sprint Start Reaction Times and the 100 ms Rule

In a 100 m final, the race can be won or lost before anyone has taken a stride. Sprinters react to a sound, not a light, and the rules on how fast they're allowed to react are some of the most argued-over numbers in sport. Starting Gunputs you in the blocks. Here's how it works, what the research says about reacting to sound, and what a good time looks like.

How the game works

After the countdown the screen stays still and you wait. After a random pause a beep sounds, and you tap the moment you hear it. Nothing on screen changes when the beep plays, so you can't react to your eyes instead of your ears. Tapping before the beep is a false start, and so is any tap under 100 ms after it, which is the same limit used in elite athletics.

Your time runs from the moment the beep actually leaves the speaker, not from when the code asked for it. On a phone or laptop the sound reaches the speaker a little after it's requested. We schedule the beep in advance and use the audio system's own timestamps, which include that output delay, to start the clock.

Use the built-in speaker or wired headphones.Bluetooth headphones add a delay that can't be measured reliably and is far bigger than the gap between grades. The iOS and Android apps won't start the test over Bluetooth or AirPlay.

The 100 ms rule in athletics

Elite sprint starts are timed by sensors in the starting blocks, which record when each athlete pushes against them. Under World Athletics rules, any reaction faster than 0.100 seconds after the gun is a false start, and the starter hears a warning tone. The idea is that nobody can genuinely hear the gun and respond in under a tenth of a second, so anything faster must be a guess.

Whether 100 ms is the right line has been argued for years:

• Some sprinters may beat it.In a study by Pain and Hibbs (2007), five of nine athletes averaged under 100 ms in at least one test condition. The authors estimated that the nervous system's part of the response can be under 85 ms. A 2009 study commissioned by the IAAF, the sport's governing body, recorded some reactions as fast as 80 ms and suggested lowering the limit to 80–85 ms.
• Others say the limit is too lenient.Lipps and colleagues (2011) analysed 425 sprinters at the 2008 Beijing Olympics. They estimated the fastest plausible reactions at 109 ms for men and 121 ms for women. Brosnan and colleagues (2017) studied World and European Championships from 1999 to 2014 and proposed limits of 115 ms for men and 119 ms for women.

We use 100 ms, the same as the rulebook. A finger on glass isn't a sprinter in blocks, and a tap doesn't have to overcome a force threshold, so a slightly generous floor is fair. A time just above 100 ms is still something to be suspicious of, though.

How fast do elite sprinters react?

Tønnessen, Haugen and Shalfawi (2013) analysed 1,319 sprint reactions at World Championships from 2003 to 2009. Men averaged 166 ms and women 176 ms. Men who reached a final reacted faster there, averaging 142 ms against 161 ms in the first round. Stakes and focus matter even at the top.

Usain Bolt is the best reminder that reaction time isn't everything. In the 2008 Olympic final he ran 9.69 with a reaction of 0.165 s, near the slow end of a field that ranged from 0.133 to 0.169 s. When he set the 9.58 world record in Berlin in 2009, he reacted in 0.146 s, while the quickest starter in that final reacted in 0.119 s. A good start helps, but the race is won over the next 9 seconds.

Hearing vs seeing

Most people react faster to a sound than to a light. Hearing turns a stimulus into a nerve signal more directly than the eye does, so the signal reaches the brain sooner. Studies differ on the size of the gap. One small study (Shelton & Kumar, 2010) found sound reactions about 47 ms faster than light reactions in the same people. In practice, expect your Starting Gun times to beat your Lights Outtimes, and that's why its grade bands are tighter.

What score to expect

Sprinters' times are measured from the gun to force on the blocks, which takes a whole-body push. Yours is measured from the beep to a fingertip touch. The movements differ, but the hearing, the decision and the start of the movement are the same, and that's what this game trains.

How to get faster

• Turn the volume up. Louder sounds are reacted to faster, and a quiet beep in a noisy room costs you time.
• Close your eyes or soften your gaze. Nothing on screen helps you, and listening hard is the whole job.
• Set, don't guess. The pause is random. Sprinters train to stay still and ready for an uncertain hold, and you should too.
• Compare your sound and light scores.If your Starting Gun times aren't faster than your Lights Out times, try a different speaker or headphones.

For more on what moves your scores day to day, see what is a good reaction time.

Sources

1. Pain, M. T. G. & Hibbs, A. (2007). Sprint starts and the minimum auditory reaction time. Journal of Sports Sciences, 25(1), 79–86.
2. World Athletics, IAAF sprint start research project: is the 100ms limit still valid? (2009).
3. Lipps, D. B., Galecki, A. T. & Ashton-Miller, J. A. (2011). On the implications of a sex difference in the reaction times of sprinters at the Beijing Olympics. PLoS ONE, 6(10), e26141.
4. Brosnan, K. C., Hayes, K. & Harrison, A. J. (2017). Effects of false-start disqualification rules on response-times of elite-standard sprinters. Journal of Sports Sciences, 35(10), 929–935.
5. Tønnessen, E., Haugen, T. & Shalfawi, S. A. I. (2013). Reaction time aspects of elite sprinters in athletic world championships. Journal of Strength and Conditioning Research, 27(4), 885–892.
6. World Athletics official results: Olympic Games 2008 and World Championships 2009, men's 100 m finals.
7. Shelton, J. & Kumar, G. P. (2010). Comparison between auditory and visual simple reaction times. Neuroscience & Medicine, 1(1), 30–32.