Myth #1 - Sending a horse around the round pen will decrease his adrenaline.
This truly depends on what speed you are "sending" the horse around the round pen. Most often "sending" a horse means at a canter or a lope. Tell me, how often do you see horses cantering or loping, especially at mock speed, and their adrenaline comes down? For some horses this can be true, but it requires the right circumstances for this to be true. For most horses, their adrenaline goes up. Especially Arabians and Thoroughbreds who are built for speed, they get more amped up the faster you make then go around the pen.
Myth #2 - Round penning a horse makes him easier to catch.