I would have to say that while there is some relation between muscle size and strength, it is a shaky relationship at best. I am a powerlifter, and I increased my bench press over 100 lbs from July 2001 to December 2001 while increasing my body weight about 7 lbs. Someone above hit the nail on the head. Lifting big weights is more about the central nervous system than it is about big muscles. That is why some powerlifters, Louies Simmons for example can continue getting stronger into their fifties, while science shows that muscle hypertrophy is exceedingly difficult past age 40.