It's amazing what a difference conditioning makes. Sergio was the same physical size in 1984 as he was in 1985, but was harder and more ripped in 1985. The slightest changes make a huge difference.
Word to the wise pros: you all have the muscle mass to do well in pro contests - just focus on coming in as hard as possible and forget about constantly packing on more mass. I seriously believe that almost any pro can qualify for the Olympia in his pro card victory form.