Assistant Stacy secures a double strand of steel chain around my wrist. Doubled, the chains have a load limit of 90 pounds. Earlier that summer, I had trained for this in the gym using weight stack cable pulls. When I got up to a controlled pull with 100 lbs., I figured I had what I needed to part the chain, since I'd be giving that a jerk and the momentary load would probably be effectively greater. Turned out I was right.