Doesn't make any sense on the surface but when you start thinking about it and you know what your looking for it makes a ton of sense.
Also, when you start looking deeper at problems over the whole body it's amazing what issues at the hips can influence.
Basically, if you have someone that has really bad tension imbalances, namely, there is alot more rectus and IT band tension relative to glute tension, they are usually going to have upper body problems.
Usually it's going to be apparent on pushing and pulling exercises. Inability to load the proper muscles.
Take this guy for instance. That pattern his body is using complete crap. He has alot more strength than that, but his body is not using the correct mechanics because of an issue at the hips.
Think about it for a second. Say you have a tremendous amount of tension on your it band and rectus and pretty weak or dysfunctional glutes. We already know the lower back is not going to be functioning properly because the hips are not functioning correctly. I think that much is obvious.
Then, what is sitting on the lumbar spine? The thoracic spine. So the problems at the hip that traveled to the lumbar spine (or lower torso really because the abdominals are not going to work properly either) are just going to magically disappear and not have any affect on the thoracic spine? No, they will cause huge problems at the T-Spine. If your t-spine function is messed up, just kiss goodbye upper body function period.
This will even effect bicep curls. Lateral raises, external rotation exercises etc..
That's why when someone gets on the board and is going in depth about GIRD and all this other horseshit without looking at the hips I just laugh. They will never get better.