The pec actually consists of two different muscles. That "ditch" in Art's pec is the shows the difference. It is not visible in people with less mass and definition. I've worked out with Art. His arms and shoulders are actually huge. They only look small compared to his chest and back. He knows that the judges are looking for something different than what he has presented in his last few contests. He's addressing that. But even without making any changes, he is definitely one of the most amazing-looking guest posers out there.