Test your reaction time:

Select the colour you want the background go and then click the "Start", wait until the background colour changes. As soon as it changes, hit "stop!". You will then be given your reaction time.
Change background colour to:  

Below is a rough guide to sprinters reaction time to the gun.

outstanding Under 0.13s
above average 0.13-0.15s
average 0.15-0.17s
below average 0.17-0.19s
substandard 0.19+s