What it warms up:
Shoulders and biceps
Yet another case of waking up the muscles on ones side of the bone and giving a pleasing stretch to the muscles on the other side. In this case, we're waking up the biceps and stretching our triceps with each bend of the elbow. The shoulders get a great range of motion out of it as well.
Stand tall and lift your arms straight up over your head, bend at the elbows to touch your back, then reverse the movement back to the beginning. You can swing your arms a bit, but don't whip them overhead. As always, move with control and care. Try keeping your elbows pointing up at the ceiling and close to your head at the top of the movement.