After class this morning, I stuck around to work on this week's pose--Urdhva Mukha Svanasana (Upward-facing Dog). I usually come to it from a Down Dog-to-Plank flow so I'm thinking about lengthening the arms and engaging the torso. Of course I couldn't hold it for 5 minutes (who thought up that dumb rule?), but I was there long enough to watch my elbows try to roll forwards and ease the work of the chest.
I'm not going to go into a long explanation here (because I already did here) about why you need to keep your inner elbow creases facing each other, but notice how much your inner creases want to twist forwards. This causes the elbows to lock and you rest the weight of your torso on the elbow joint, instead of keeping the chest engaged supporting the body with your pectoral muscles. Just try it and see...elbows roll forwards--easy, elbows face each other--arms start to shake.
A common instruction for Up Dog is to open across the chest and this action can easily lead to rotated elbows. As you open the chest, really concentrate on keeping the shoulder blades down in back, lengthening the neck and keeping the arms in line as you press your palms to the floor. Breathe into the work of the chest and upper arms...because, believe me, there will be work.
Then lift back to Plank and up (?) to Down Dog as a release pose. You bionic yogis may move into this from Chatturanga Dandasana, but I usually end up on my belly as my arms give out instead of curling up to Up 'Dog. I guess there's another goal to strive for...
(If you want to read more, here's an even earlier post on the wrist joints.)