There are four runners in each team and three exchanges.
The receiver of the baton has an acceleration distance of 10 metres before the exchange zone, which is 20 metres long.
The baton must be exchanged within the exchange zone, otherwise the team is disqualified.
There are two common techniques of baton exchange.
An over-hand exchange means the baton is exchanged from above the receiving athlete.
An under-hand exchange means the baton is delivered from underneath.
As soon as the receiving athlete starts accelerating, he/she cannot see delivering runners so the technique has to be very definite.
In the 4x400m, the first three curves are run in separate lanes, meaning the whole 1st leg and 1st curve for the second runner.
After this they break to the inside of the track.
In preparation for the 2nd and 3rd exchange the receivers must line up in the same order as the teams are 200m before the exchange.
The exchange phase is challenging as several teams often exchange at the same time.