Elevated reverse plank

On Facebook/insta and the blog, GB suggested elevated reverse planks to build shoulder extension. Is my son's form here good enough for carryover to the second iM?

Exercise must be SPECIFIC to have a decent carryover. ask yourself if the bodyline is the same of standing shoulders extension. 

In order to take all the benefit from elevated plank, he should hold a neutral pelvic rotation as demonstrated in the shoulders extension.

From my experience for shoulders extension you need time and , rotator cuff muscles need time to adapt. stretch the anterior chain will provide the necessary help.