Ed, I'm probably not the best to answer this because I haven't tried it myself. Saying that, I did watch the U of T Parkour club practice every week, and talked to quite a few of the members, because they practiced at my favorite (warm weather) study spot.

I have to say that these guys are extremely well conditioned. They start practice off with a twenty minute run, take a water break, then do sprints, pushups, and squats. After that, most of their conditioning is done by using the space around them as an apparatus. After the new guys learn the basics of break falling, they begin to work on jumping. Initially, they just jump from a squat position across the grass, then roll and stand. After a little of that, they find a path that is lower than the surrounding ground, and jump from side to side, landing in a breakfall. They also hop up stairs, taking them two at a time. There is a large statue in the park, and some of the more advanced guys use that in various ways, for pullups, as well as balancing on. I saw a few use a tree stump to do a headstand on, and then do raises in that position. They also practice railing jumping, initially not to high up, but as they progress they go higher and higher up the stairs. It was amazing to see people who had little strength at the beginning, being able to bound up a stair rail in five or six leaps, hoping to either side, in a matter of a month.


The training leader seemed to have things fairly well organized, and it does seem that they follow a pretty tight protocol, taking someone from beginner to advanced.

Aside from the training sessions, they meet in the park, warm up, and then go for a free run. These guys put ninja's to shame.

As for injuries, apparently they are pretty common. Mostly twisted ankles, and sprained wrists--but occasionally concussions, and cuts that need stitches.

Here are a few videos that show the potential dangers of this sport very clearly. They highlight the need to actually learn from someone who knows what they are doing. Warning, some of this stuff hurts just to watch...

http://ca.youtube.com/watch?v=vME2BBzxK38

http://ca.youtube.com/watch?v=Ezi04hhcYm4

http://ca.youtube.com/watch?v=P4wOByXdM1M

--Chris

extreme game of tag
http://www.youtube.com/watch?v=6qhgIdP3l3I&feature=related

David Belle
http://www.youtube.com/watch?v=x98jCBnWO8w&feature=related

Russian Ninja's
http://www.youtube.com/watch?v=XVQNt64PxfE&feature=related

I train Parkour myself, very intensively.

I've trained for around 3 years now, with a huge amount of strength building along with it. I'll tell you right now this has been hugely more beneficial to me than any martial arts class.

I train twice weekly, Thursdays and Saturdays. These are my days where I just go out and practice my Parkour, a lot of strength is required. When I first started Parkour I was pretty young, but really weak. The massive gains I have made from Parkour have been well... massive! My bodyweight strength is quite high and since my relatively recent move to weights as well my strength level has exploded!

Injuries are really down to yourself. If you're injured it is almost always your own fault. Any of the times I've been injured have been down to not concentrating enough or just plain silliness.

I am self-taught, as when I first started the Parkour scene in Britain was quite small. This meant that although I made mistakes early on, I feel it allowed me to build my bodyweight strength quite effectively. Since there was no-one telling me HOW to do things, therefore I had to work it all out by myself using my own resources. These days there is a wealth of information, help and information for new practitioners. However! I digress, Parkour is excellent, open for all ages. The age range in my local community (http://www.glasgowparkour.co.uk/) is quite large, from 13 to 30!

Myself, I am 17. Anyone with an interest in this I urge you to try it out! I know many of you are from America so I recommend taking a look at http://www.americanparkour.com/

however my favourite Parkour website is based in Britain and has the most experienced practitioners in the world active on it:
http://www.parkourgenerations.com/

I'm open to any other questions people may want answered, also the websites I've linked to have a large amount of information as does the Wikipedia article.

Cheers,

David

Im into it a bit as a hobby
not so much parkour as tricking, but its easily intergrated.
good fun til your knees wear out

your knees only wear out if you don't condition properly

see this; http://blane-parkour.blogspot.com/2007/04/dilution.html