Alright guys, I ran into a little contention over at the crossfit messageboard about this. I believe someone asked whether or not the hips come back any during the dip/drive of the jerk. I hadn't done much research at the time, but I know that the lifters at my place naturally let their hips come back slightly followed by a strong extension before dipping under the bar.
Now, what I heard from most people over at CrossFit was that you should keep your torso as vertical as possible, and not bring the hips back, so the bar doesn't drop forward, and you maintain the straightest bar path. This bothered me for a few reasons, and I'd like your thoughts.
1) The vertical torso/no hips back (I have to think of a better word for it!) postition would have to limit the involvement of the hamstrings/posterior chain. All other movements in weightlifting depend on these muscles, why not carry over to the jerk?
2) While keeping a vertical torso and allowing the knees to come forward, I felt the weight roll to the balls of my feet. Allowing my hips to come back, things still felt "nice", and I could feel the weight over my heels.
3) I may be wrong here, but is a straight bar path the most efficient? Seeing the bar path for both the clean and snatch in experienced lifters, it certainly is never a perfectly straight line! Sadly our bodies don't conform to nice straight lines.
Lastly, I had two lifters try both versions with moderate weights, and both felt like it took a stronger effort to get the weight up keeping a vertical torso.
I'm going to pull this quote from an article on jerk technique, from www.dynamic-eleiko.com:
"The hips shift backward during this movement to counter balance the "toppling over" effect of the barbell.
If the lifter bends the knees for the half squat with the trunk in a vertical disposition, the common center of gravity of the athlete barbell system will shift forward along with the knees and ankles (40). This can reduce the effectiveness of the muscles of the lower extremities because the barbell shifts at a slight angle away from the lifter and increases the moment force on the aforementioned muscle groups. This, in turn, further increases the "toppling over" effect. "