Here is part of an article I wrot on that subject many years ago. There have been a million articles and quite a few books written about the importance of heavy leg/back work to make your WHOLE body grow.
I know there are some people on this board that are dying to add some serious mass to their frame. Want to know the cheapest and MAYBE the most effective way? SQUAT!
I have met people that never gained shit until they got on a simple program that revolved around heavy squatting. I have had drug free people gain 20 lbs in three months doing a simple routine of 6 or 7 exercises with the emphasis on killing yourself squatting, and heavy eating. And I mean 20 lbs ALL over not just the legs. Here is an excerpt from an article I wrote for Hardgainer Magazine many years ago, and yes I know hardgainer mag is aimed at drug free trainees, but the same principles apply:
The typical hardgainer can forget about making big gains throughout the body until they get the thigh/back musculature growing. Think about it this way, if your body is not very efficient at growing muscle tissue and your current routine is like that of most trainees, (what I call the double B's, bench and biceps) how much of a demand have you placed on your body to become more efficient at growing? Working chest, delts, tri's, and biceps works approximately 10% of your overall lean body mass. Working hard on deadlift's (bent legged, Trap Bar, or sumo) or squatting (not necessarily at the same time) works more like 70% of your musculature at once and sends a STRONG message to your body to GET BETTER AT GROWING NOW!
Because the demands on your metabolism are so great when doing these movements the results are also great. But like anything worthwhile in life it comes at a price: brutally hard work done consistently with ever increasing poundage's. The original "recipe" for success for those that were previously unable to register significant gains in size and strength was the 20 rep squatting routine with one set (after warm-ups) to failure done along with a handful of other basic exercises, no fluff, just brutally demanding hard work done infrequently with an emphasis on heavy eating.
And no, you don't have to do 20's, anty rep range will do. Start squatting heavy and watch your whole body grow.
Iron Addict