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The Premier League has voted to introduce permanent concussion substitutes.

Clubs approved the trial during a meeting on Wednesday, although there is no start date yet.

A concussion is a mild brain injury normally caused by a bump or blow to the head.

Teams will be able to make up to two permanent substitutions in the event of head injuries, as well as their three regular substitutions during a match.

The Premier League is the first competition in the world to agree to the trial.

The International Football Association Board (Ifab), the body that makes and approves the laws of football, approved the trials of concussion substitutes at a meeting in December.

Fifa, which governs world football, has already announced it will trial substitutions for actual or suspected concussion at the Club World Cup in Qatar later this month.

Concussion is a type of head injury. It happens when someone gets a significant bang on the head - so much that the brain is shaken and knocks against the inside of the skull.

This causes the nerves and structures in the brain to be altered, which means messages aren't sent around the brain in the right way.

If a person is concussed, there are ways it can be spotted. For example:

It can be serious and it might take someone several days to recover if they have a very bad bang to the head.

Some people think that in order to get concussion, you have to be knocked unconscious - but that isn't true.