Sean Conway has written a straight forward blog post about the 4 elements of trail running, which is both a good read and has some really good points that anyone doing long runs out on trails should really think about.
Here’s the thing. In martial arts, in particular when studying and practicing form, you work on making the movements second nature. In other words, training should be something that makes running or moving along trails your natural state. Learning to be aware of your body’s needs, strengthening weaknesses and finally, knowing how to cope with those emergencies (like a suddenly drop in temperature) in an almost isntinctive way is what makes up the 5th element of trail running. Being able to move with almost inhuman efficiency.
Now this is just my thoughts and ideas on screen. If you make running trails your natural state, your body will respond by adapting. As a species, we are incredible endurance machines with the capacity to adapt on the move, and of achieving what our modern, sedentary and comfortable lives would deem impossible.
The limiting factor in this whole thing is our preconceptions of what is physically possible.