I am really enjoying your discussion on my post-
1. Thanks JH for your comment on the collapsing of the pelvis in the sagittal/frontal planes during the jump. Very likely. The point is the researchers only looked at one plane/one direction/one joint. I think we would all agree that strengthening IR in isolation probably wouldn't do much to prevent ACL injuries in female athletes.
2. Again, you were all on target with looking at the subtalar/midtarsal joints of the LE. KP began by suggesting ankle hypomobility, with JH & ATCREF the opposite. I think you are both correct. As the ankle runs out of sagittal plane motion, it will steal it from the other two planes, usually choosing pronation. This & the planus foot structure will usually (not always) cause hyper IR at the tibia with a chain reaction up to the femur. If the timing of the IR in the femur & the tibia is out of sync, ACL beware.
3. Bonnie, you are on the right track with your idea of a same side arm reach @ shoulder height to block that femoral IR. All you need to to is bring the contralateral arm over with it. JH mentioned it would not be a strategy that he would use, & that is fine. The point is using other drivers to assist the hip in planes/directions it is weak in. Assuring the knee/hip/ankle are all going in sync to protect the ACL. Of course, as the hip gets stronger it will be necessary to train them out of sync so each segment is strong enough to stand alone.
I am aware that there are many commercial programs out there that teach the importance of the hip/knee/ankle staying in a straight line during jumping. I know these programs have been proven to reduce ACL injuries. However, I don't believe this happens out on a soccer field or a basketball court. Can you imagine coming down from a rebound and saying, "would you be a sweet heart and move your foot out of the way so that my LE can stay in sync". I prefer the Gray/Gambetta "lower extremity performance & prevention" video.
Thanks JH for reminding us that all muscles have a triplanar function, including the quads.