As a gym owner, I watch people come in and go out all day long, the same people, and hopefully new people day in and and day out, week after week, month after month, year after year. And let me say that I am 100% convinced that the number one reason that people don't grow is what I call "UNDER LIFTING!!!!!!!!!!!!!!!" It actually gets to the point where I'll get pissed off watching a guy doing a set of db rows for 8 reps with 20lbs. when I can tell by the expression on his face that he could easily do it with 60 pounds. Since I'm the owner I can do these things, so I'll go over to the guy and ask him what the hell he's doing and have him get the 60 pound db and do the set of 8, which of course he can. But what happens, the next week when he's doing back again?????? He goes and gets the stupid 20 lb. bell again and sticks to it!!!!!!!!! I don't even bother with these guys anymore, cause ya can't help someone who doesn't want to be helped. I don't leave the gym to anyone else, cause basically I don't trust anyone else with my "people" so I know each and every person who works out there, and after 5 years of watching both men and women work out, the ONLY one's (and unfortunalty it's only a small handfull) who have many any serious gains are the one's who consistantly push and challenge themselves with progressively heavyer weights, or by using "intensity" techniques. I agree with those of you who mentioned diet as a factor also, but the bottom line is that if you don't stimulate the muscle to grow in the gym, not even the best of diets is gonna make a damm difference. O.M.G.