And at the same time that the radius is decreasing between this bone and our hinge, our joint, our muscle in the back, our tricep muscle is actually elongating. It's stretching out, it's extending. And the muscle that contracts is known as our agonist, while the muscle that is elongating is known as our antagonist. So when the angle is decreasing and when I'm pulling my bones closer to my body, our bicep contracts, it's the agonist. While this, our tricep, is elongating, it's our antagonist. On the other hand, let's look at diagram B in which the opposite is taking place.