I've been lifting weights at my gym about 3x a week since Oct '07. I've seen a significant increase in muscle mass and strength. Is there anything natural I can do increase my work out's effectivness or grow more quickly?

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You need to overload your muscles to advance. To gain strength, increase weights in your workout. To increase muscle size, handle heavier weights and increase sets you do. To increase muscle endurance, decrease your rest time between sets or increase number of reps or sets. Part of constant growth is never allowing your body to get use to one specific training protocol. Vary exercises, sets, reps, weights, rest times, even angles of pull on your muscles. Confuse muscles to keep them growing!

Try reading muscle and fitness helps me eat tons of protein too

Work to failure, but not all the time. Working to failure is horrible, but it really tells your body you need bigger stronger muscles. Make sure you have a really good spotter, so you don't get injured.

Don't do it too often, or you will overload your CNS.

Once or twice per workout is plenty.

Are you concentrating on big compound lifts like squat, deadlift, bench press, military press, dips, lunges, bentover rows, stiffleg deadlifts, etc? Those are the mass builders. Make sure you are lifting heavy enough. Around three sets of eight reps using about 80% of your 1RM usually produces good results. If you can do more than ten reps, you need to increase your weight.