Busting doors is very easy. Distressingly easy from the homeowner's perspective.

normal door jambs

Kick at the lock (lift your knee chest-high and straighten your leg through the door, leading with the heel) -- the lock tears through the wooden jamb and you're inside. On normal doors, slightly below and "inside" the lock tends to be the optimum -- the extra bend in the door when you kick, plus the extra horizontal strength of the flatter angle, helps burst the jamb. With practice, you should be able to walk through the average front door without slowing down. And no, you don't have to be big -- I'm 62kg.

multi-locks

The door-bend won't help you much-- just go for the middle of the locks. E.g., halfway between 2; in the middle of 3. Martial arts, gymnastics, or acrobatic dance (e.g. ballet) training will help you here, as the hip/sacroiliac strength lets you easily transfer impact and then weight through the kick.

steel jambs

The only useful door. Here, you have to tear the entire jamb out of the wall, or at least its mounting points. Your leverage points are the latch and the hinges, so go for the mid-point of all. Green wood or tough wood is actually harder to burst through than steel, as a jamb, incidentally, as the wood's "give" protects the fastenings of jamb to wall/surround. 2 choices:

• kick at centre of door and the doorbend helps you
• "use the hip"-- crouch a little then stand up and into the door, leading with the hip & using your weight. Usually takes 3-5 goes. Charging with the hip is a useful accelerator if you have useful bodyweight.

Incidentally, this is about the only time a police door-ram (or a fire extinguisher) is useful/adds value. And if you have one/there's one nearby, just go for any key single point: either the latch on a single-lock door, or the hinges on a multiply-locked door. Once they're broken, just kick the door through.

:) this has been an announcement funded by the Australian tertiary education system.