Many people face challenges with this stretch, which is executed from a standing position.  Attempt to clasp your hands behind your back, one from above and one from below, as shown in Figure A.  If you can reach, hold the position for 20 to 30 seconds; then reverse arms to stretch the other shoulder.  If your hands remain a few inches apart from each other (see Figure B), use a towel to complete the stretch (see Figure C).  Walk your hands up the towel, positioning them as close together as possible, then reverse arms.