Starting blocks are used for all competition sprint (up to and including 400 m) and relay events (first leg only, up to 4x400 m).[15] The starting blocks consist of two adjustable footplates attached to a rigid frame. Races commence with the firing of the starter's gun.[15] The starting commands are "On your marks" and "Set".[15] Once all athletes are in the set position, the starter's gun is fired, officially starting the race. For the 100 m, all competitors are lined up side-by-side.