Here's a http://www.flexonline.com/quads_bodybuilding_weightlifting/training/157 concerning working the quadriceps hard while going a bit easier on the back. One of the exercises suggested is hack squats.At the gym, the hack squat machines are among my favorites. I can work the quadriceps without worrying about balancing a bar on my back, as in regular squats. There's two types of machines available at my gym; a Hammer Strength piece that's plate-loaded and doubles as a high pull unit, and a machine in which the user stands on a plate and pushes up after bending and getting the shoulders under pads.

This weekend I did 11 sets, 8 on Saturday. Normally I wouldn't work the same muscle group a second straight day, but I made an exception on Sunday.