The debate has raged on with many people for a long time. What is more important, heavy weight or proper form? Is there a way to merge both together?
The fact is that both items are important, but you need one before you can get to the other. That's right, I believe that form is essential for making progress with any lifting regimen.
In order to get good results with each muscle group there has to be the proper amount of contraction to recruit maximal muscle fibers. The only way to get here is to lighten up the weight and improve your form. Each exercise is designed to stimulate the targeted muscle group in a very specific way. Small changes to the form will change how the muscle group is hit.
Think about the shoulders for a moment. They consist of front, side and back delts. Depending upon the execution of an exercise for the side delts you may inadvertantly hit the rear delts. This is because your form is sloppy. If you want to insure tha tyou hit just your side delts you have to insure that your form is perfect. This takes practice and at times, a trainer to observe you as you do the lift.
Proper form also involves activating the right muscles during a particular movement. All movements you do involve keeping your core muscles tight. In addition, squats (for instance) involve recruiting the glutes and hamstrings during the movement. If the glutes are not activated during squats there can be major issues later (including the higher potential for injury).
It is true that heavy weights will increase your strength and the size of your muscles. At the same time, using proper form will eventually get you to the heavier weights. To some this is a humbling realization. It was for me.
I was the guy who threw 45 lb. dumbbells up for side laterals. My form was awful and my results showed this. When I began working with my trainer he took the weight down to 10 lbs., but insisted upon perfect form (elbows higher than wrists and pinky turned up at the end of the movvement). As a result, 10 reps with the 10 lb. dumbbells felt like 20 reps with the 45 lb. dumbbells. Additionally, my shoulders look better now than ever before as a result of this approach. Slowing down and using lighter weights with good form has really helped.
The bottomline is that both form and heavy weights are important, but you must have form before attempting heavy weights. Through the use of proper form your lifts will gradually increase and soon you will be back to the heavy weights you were accustomed to. Since you are trying to transform your body, I suggest that you check your ego at the door and work on your form.