I thought I had talked about this before in an earlier post on wrists, but after a leisurely scroll down memory lane, I realized I hadn't. My teacher used to instruct us to place our hands so that the wrist crease was parallel to the top edge of the mat to prevent the elbows from hyper-extending. I never realized why that helped until I did the reading for that earlier post. By lining the wrists up, you "square" the insertions of the radius and ulna of the lower arm. When they are crossed (elbow creases thrust forward) the elbows lock and you end up holding the pose by resting the bones against each other, instead of using the muscles of the chest. Sort of the same logic behind engaging the thigh muscles in Trikonasa or Virabhadrasana II so that the knees don't lock and make the pose rigid.Give it a try for either Urdhva or Adho Mukha Svanasana, various arm balances or Plank. It is much harder to hold these poses when the bones are un-locked; therefore strengthening the pectorals and biceps (which is gentler on the wrists).
I think my students often wonder why so much time is spent arranging the hands and arms for Dog. But once they are up, they notice the difference in the work of the torso (I hope) and it gives them a focus for the arms. I've also been sliding a rolled blanket under their heels if they are quite far off the floor to give them some support so they can lengthen behind the knees...but that is a discussion for another post.
P.S. I highly advise a glance at old posts. Like flipping thru a photo album, it's fun to reminisce about what inspired a certain article or what you were thinking when you had to rant (or rave). I wrote my 100th post a few weeks ago and forgot to commemorate it...looking back is an acknowledgement of all that work. Whew.

