Something a lot of people seem to be missing, especially the "STRENGTH = SIZE" proponents is that WORKLOAD is NOT EQUAL to the WEIGHT ON THE BAR!!!
As people keep trying to drill into your brain over and over, it's about HOW YOU LIFT IT. Yes, to get bigger muscles you have to increase the stress on the muscle, but that DOES NOT MEAN YOU HAVE TO INCREASE THE WEIGHT.
People who have huge quads and squat three plates do it with perfect form, very smooth, controlled, focus on the negative, all this serves to make the muscle work much harder with the fixed resistance (315 lbs). You will see kids all the time throw on 3.5, 4 plates, even more who have gimpy little legs. Some of that is due to neurological efficiency, and some of it is do to SHITTY FORM. Powerlifting form, for bodybuilding purposes, is SHITTY. They do everything in their power to LESSEN THE WORKLOAD on their muscles, so that 900lb squat becomes equivalent to 500 lbs work that the muscle has to do -- they change the leverages, have bad depth, use special suits, distribute the load across as many muscles as possible, etc etc.
When a powerlifter switches over to bodybuilding a la matt kroc, do you see him saying "well gee I've squatted 1013 lbs so I guess to get bigger legs and glutes I need to squat 1015... after all, size = strength right???" NO! He goes down and works with weights in the 400-500 lbs range, changing his form and number of reps so that the MUSCLES have to do the most work, no more utilizing leverage, crappy form, get it up at all cost, mentality, which are all designed to make the resistance on the bar translate into as little muscular work as possible.
So yes, you have to increase the stress on the muscles to make them grow... looking around the gym, i see 99% of kids could use lighter weight and better form to achieve more massive muscles.
In bodybuilding, it's not about how much weight you can lift, it's about how much you can get the weight you are lifting to work for you. Look at ANY big guy in the gym. Perfect form, I guarantee it. Sure there is the occasional Ron Coleman, Branch Warren, total freakish, indestructible joints + they're probably showing off for a video whenever you see them.
In summary: yes you have to increase the workload on the muscles, however in most cases this does not mean increasing the weight on the bar!!!
For the record I put ten pounds on my legs, with extremely noticeable visual changes in 2 months never lifting more than 115 on squats. I did one set for time, 2 minutes the first week, adding 20 seconds to the clock every workout up until about 5 minutes. Followed up with two excruciating sets of leg extensions no more than 135-150lbs and a couple leg curls. Most people would say that wouldn't work. Too many reps, not anaerobic work, wrong energy systems etc. etc... of course they have never tried it for themselves.
