Heavy, spine crushing squats seem to do the trick for me. I go with low reps/low sets. Squats produce so much stress and take so much force that it is easy to over do it in my opinion. People argue your legs are the biggest and strongest muscle(which indeed is true), but from this they conclude that it's hard to overtrain them and you can do rep after rep on set after set. They either are'nt going heavy enough or are using incomplete from. Fact is it's far from every day occurances to have to squat 500 or 600 pounds through a full range of motion. This exerts far more stress than they are used to...hence the insuing hypertrphying and strenghtening of them. I personaly do 3 sets at 6,4,2 respectively. No high rep endurance marathon sets for me. I've done them and and might as well just run on the treadmill because all I get from them is cardiovascular training and no leg stimulus. Every workout I try to add pounds to the bar. This stimulus progression is what forces the muscle to keep progressing. Following squats I do heavy leg extentions. Again no 30 rep "shape" sets. 3 sets here 6-8 reps. It takes poundage to stimulate my legs not reps so I go heavy. Quads are hands down my best muscle group so I have found how to best train MY quads. Heavy weight, low volume, intense focus. That's my formula. Bottom line is the foundation is heavy squats.