Supine snow angels - bent arms (Shoulder external rotation AROM, sliding arms overhead, supine)

Lay down on your back, with your knees bent and feet flat on the floor.
Take your arms out to the side and bend your elbows to 90 degrees.
Try to lie your forearms on the mat, or as close to it as you can.
Bring your elbows down toward your side, then slide your arms up as high as you can over your head, keeping in contact with the floor at all times.
Your elbows should stay at 90 degrees throughout the movement.