Orienteering Obstacle Course
Sam Smith

Here is the training I wish I could find the time and/or energy to do:

Go to your favorite park and tape off a 200 to 400 meter loop that includes some physical obstacles that will force you to use more than just your legs. You don't want an easy trail run, you need something that makes you twist and turn, bend over, jump, climb out of gullys and over fallen trees. The idea is to exercise all parts of the body. 

Do several circuits with a break in between. 

Don't do this more than once a week, and only if you already have a base of 15 or 20 miles a week running...