The pull-up is a simple enough movement. All you need is a bar or a tree branch or a ledge. Just something to hang from. Then, you pull yourself up. As simple as it seems, anyone who has spent a decent amount of time doing pull-ups knows that there are countless nuances and variations (just like running) that make this movement much more complicated.
The difference between a strict pull-up (no lower body movement at all) and a kipping pull-up (the crossfit version) is huge. It's hard to call them both a pull-up. But just like with running or climbing or anything else, the way you do something is always more important than the fact that you did it.
If you've read one of these columns before, you know that I'm constantly talking about endurance athletes cross training in maximal zones. You spend nearly all of your regular training at sub-maximal levels, so when you cross train, I think a good portion of it should be spent maximally exerting yourself. The pull-up is no different. Strict, full range of motion pull-ups are always a great exercise and a good way to activate your posterior chain, but adding a power component by attempting to explode your chest toward the bar makes this exercise more intense and more beneficial-- especially for a trail runner.
The majority of our lives are spent (as you probably are right now) sitting with our shoulders rolled forward and our hands and arms in front of us, typing or holding a screen up to our faces, grabbing a steering wheel, shoveling food in our mouths, etc. So, whenever you get the chance, it's beneficial to undo some of that crap life is doing to you and it will leave you with much better posture, more balanced joints and less susceptible to injury.
Remember: as humans, we press and we pull. We do them from different angles but as far a compound upper body movements, that's all we do. Most people are in the anterior of their body all day, in the ways I just described (our lives are set-up for it) and then they get in the gym and spend the whole time pressing (an anterior movement) when they should be pulling and working the posterior muscles.
A couple of things to note in the video: If I was strong/powerful enough to start at a dead hang (arms straight) and explode all the way to the bar with my chest, I would be doing that. As it is, I need a little kip in there to help bring my elbows closer to 90 degrees before I can get my chest to the bar. Despite having to kip (essentially bending my knees and providing a little bit of forward momentum) I still always return to the dead hang position and don't short the range of motion. Full range always!!
Adding a power aspect to your cross training will make it more fun, more engaging and give you something to work towards. You could sit on a lat-pulldown machine or you could try to bang your chest against the bar and add explosive upper body strength while developing a skill and staying mentally engaged. You'll notice how much of a core exercise this is as well as a good way to add some full-body coordination. And, if you feel like it's getting too easy, then you move on to the muscle-up. Always some place to go moving forward...