In action movies, the hero never has a problem smashing through doors - one solid kick is all it takes. In reality, gaining access to a locked room is much harder; but not always impossible. This infographic "breaks down" how it's done.
The graphic below comes from the suitably named Art Of Maliness website. It explains the most effective method for kicking a locked door down when no other tools are available or time is of the essence.
The trick is to kick the side of the door next to where the lock is mounted (near the keyhole). This is typically the weakest part of the door. At the same time, drive the heel of your other foot into the ground and lean into the kick.
While it would look a lot cooler, attempting a flying kick isn't advised. Neither are shoulder barges, which are more likely to result in an injury.
Regardless of how "tough" you are, you should also avoid doors that opens towards you. As Art Of Maliness notes in its accompanying blog post:
If the door opens towards you, kicking it down is going to be next to impossible. Kicking a door down is best employed on a door that swings away from you. You can tell which way the door opens by checking the hinges.
For more tips on booting doors down, check out the link underneath the infographic.
[Via Art Of Maliness]