Hatfield is a damn legend in this sport and science. He's one of the oldest guys who vocally pushed for a scientific yet applicable approach to training and would slam the old long endured aerobics freaks.
Back in the day when there was no internet his articles and books were awesome. If you can get your hands on an old ISSA handbook, a lot of what he preaches is in there. I have all his old books he wrote too. Awesome guy and the first guy to squat 1008 pounds like a damn freak! He certainly practiced what he preached.
Back in those days he was hooked up with Staley and they created the ISSA, which I still reckon is one of the better world certifying institutes for PT's. Dunno how they have become nowdays though.
Here's an old vid