This article is the first in a series meant to correct common mistakes I (and my fellow trainers) see at the gym. Stay tuned for the whole series so that you won't be the person that everyone loves to laugh at.
First off, go read the article on Lat Pull Down at Stumptuous.com, a weight training site for women. Not so much because the descriptions are excellent (although they are) as because they are hilarious. And we could all use a little more hilarity in our lives, yes?
So here's what a dumbass does (don't worry; I'm using super-light weight on this):
By the way, please ignore the hypermobility of my shoulder joints. The kinds of people who generally do this exercise (i.e. big musclehead wannabe bodybuilder types) don't have the kind of swimmeresque flexibility in their shoulders that I do. They look much more ridiculous using this form.
I think that most of you knew already that this is an improper way to do a lat pull down. But here's the run-down from a professional point of view: it's not "wrong," per se. Check out exrx.net's take on it; notice that there's a front pull down and a rear pull down. Different exercises. Different purposes (or that's what a dumbass at the gym will tell you).
The rear pull down is a high-risk movement, at least for most people; it takes the shoulders into hyperextension and forces you to use internal rotation of the shoulder under heavy load to complete the movement. And you should never ever do that--it's stoopid and makes everyone in the gym think you don't know what the hell you're doing.
It also places unnecessary pressure on the anterior shoulder capsule, which is bound to cause problems later on, and unnecessarily stresses the muscles of the rotator cuff. If you stretch out the ligaments in the shoulder capsule, they're not going back to their original length. And if you tear the muscles of your rotator cuff, you're going to be at increased risk for subluxation and dislocation for a long, long time.
Furthermore, although I am not a good example of this, most people don't have the functional range of motion to even externally rotate/hyperextend their shoulders far enough to yank a bar behind their neck, so they end up excessively flexing the cervical or thoracic spine. And can you imagine if the cable on the machine broke and that pull down bar came crashing down on your excessively flexed neck? And even though I have the range of motion to pull the bar behind my neck, it's because my shoulders are hypermobile; it's generally a bad idea to overload a hypermobile joint. So like I said before: it's a high-risk movement.
But there are times when it's acceptable to complete a risky movement in training. For example, it can be risky to rotate and flex your spine simultaenously. But that's a movement that's worth training if you plan to use it functionally, like for a tennis serve. With high-risk movements, the main question is whether the benefit outweighs the risk.
And in this case, it doesn't. There's no reason I can think of that you would need to torque your shoulders in this way. If you're looking to increase the size of your back by including lat pull downs in your routine, you're barking up the wrong tree. The fibers of the latissimus dorsi run in such a way that a front lat pull down is going to be more effective in increasing their strength and size. And if you're wanting to specifically train the shoulders or biceps, there are many other more effective (not to mention less risky) exercises for accomplishing that.
So to conclude a rather long-winded post on why only a dumbass would conceivably execute a lat pull down in this way, here's how you should do your lat pull downs.
Got all that? Sit up straight with the shoulders broad and the chest lifted. Tighten the core so you don't hyperextend the back. Keeping the shoulders broad, grasp the bar at a width about 1.5 times as wide as your shoulders (in the video, I use a bar that allows me to pull with neutral rotation, which is a more natural movement for me and much kinder to my FUBAR shoulder). Initiate the movement with your lats by pulling your shoulder blades down your back. Then allow the arms to follow, coming into a "W" shape.
And this is just me and the other trainers goofing off (we see people, usually older people, doing things like this all the time):
And remember, like Stumptuous.com (and Men's Health too, gentlemen) says: your eventual goal in all this should be doing pull-ups. You wanna take yourself from dumbass to badass? Do pullups!
I'm happy to address any questions in the comments, and if there's another exercise you'd like me to snark at, don't be shy in suggesting!