The other day while running, I finally got up enough nerve, and felt I had enough endurance to do some parkour on the way back up Mountain Ave (on the west side of the street, obstacles are sparse, but on the east side there is random rock art scattered about and different levels of curbs). A few observations:

---even the minimal tricks I did (basically, proto-tic tacs, jumps for accuracy, and balancing) take a bit of extra effort, and are also just fun, and so wear me out much faster than regular running, as I begin to run faster with...uh..glee, I guess

---breakfalling training is useful - not just potentially, as with me almost eating it several times, but also in the principles it teaches; for example, I didn't realize, coming from a high leap, that I could 'reach' for the ground with my legs in a similar fashion to the way you never, ever 'reach' for the ground with arms when falling...from what I experimented with, corroborated with reading, I think a certain kind of reaching is necessary, but only with the body integrated into absorbing the impact force

---which leads to the third observation, that (in my opinion) parkour is kind of a yielding art (like aikido, jujitsu, and judo) with one's self and environment. That is, half the point of it being maximum effeciency in movement (like any martial art), one has to yield to and blend with their own momentum, so one is worn out by muscling through things, and yielding to and blending with one's momentum for use in vaults and jumps, and in dispersing the impact energy of landing and falling through tic tac kind of stuff, rolls, or breakfall principles.