I don't believe it, but will give it a tiny benefit of a doubt. Fletcher was around Gold's Venice in the early 90's, and I doubt a guy could stay natural in that environment. That being said.....
It's all about bodyweight, I can believe someone 275+ lbs perhaps putting up #500 naturally. There were guys doing close to that naturally in the late 40's-early 50's. It's a tough number though.
Also I'd like to see his 3 lift total, every once and a while you'll see someone with a totally outrageous pet lift, but when you look at the other two, they're strong average. I've seen it a lot with the deadlift, just as an aside.
