There was a really nice post on this subject on the ThinkRunning Blog a while ago. Hip alignment is also talked about in detail on the BK Method DVDs that I reviewed in earlier posts. I feel that this subject is important, because poor hip alignment is a fairly common problem. Also, this element of running technique is often overlooked, or at least not emphasized, in the Pose Running materials I have looked at. As a result, I want to help raise awareness about this aspect of running technique, because I get the impression that there is not wide spread recognition of this problem in the Pose Running community.
When running, the pelvis should be pulled up on the side of the non-supporting leg. However, on many runners, it is fairly common to see just the opposite. On some runners the pelvis actually drops down on the non-supporting side. Below is another one of my stick figure illustrations that I hope will clarify this point.
What this picture is attempting to convey (other than the fact that I have limited potential as an artist), is that when the hip is pulled up with the non-supporting leg, the technique is sound, and when the hip is dropping down, the technique needs work. The runner on left has the right side of his hip pulled up at a slight angle from the neutral position on his non-supporting side, and this is correct. The runner on the right has his hip dropping down slightly from the neutral position on his non-supporting side, and this is incorrect.
A dropping hip is usually a sign of weakness in the hip abductors. So if someone has this problem, clearly these muscles would be a likely area to work on. Here is a better illustration of this subject that I found at http://www.totaljoints.info/REHAB_postoper.htm.
Here is an excellent video on YouTube that discusses this topic in much more detail.