The other day one of the guys at my gym was asking me if he should keep training heavy while he diets down. I immediately thought back to my years of competing, specifically 2007. I made a huge effort that year to train in the 6–8 rep range throughout my entire preparation. Not surprisingly, that wasn't my best year of competing.
Because I'm competing again this year, I thought it appropriate to outline why you must continue to train heavy when getting ready for a show or when just trying to get flat out ripped. When you're dieting, your body is eventually going to slow down your metabolism and try to conserve energy. Muscle is very costly as an energy source, so naturally your body will want to start shedding the hard-earned muscle you worked so hard to build up. Muscle raises your metabolism, so dieting is going against muscle maintenance. Remember, the body always wants to maintain homeostasis. It wants to use as little energy as possible and it will fight you every inch of the way when trying to lose body fat. The one way around this (although you will inevitably lose some muscle) is to continue to lift heavy weights.
If you can supply a ‘good enough reason’ to your body for having that muscle by imposing a large demand/stress on it, you will maintain much more of the muscle than if you just went into ‘pumper mode.’ One of the best bodybuilders I've ever seen, trained with, and competed against (Tim Martin, who is an IFBB pro) is known for training heavy as hell even when getting ready for a show.
Another reason to continue to train hard and heavy while dieting is mental in nature. I used to get pissed off at ‘globo gym’ when I was getting ready for a show and some other competitor said how tired he was and how he couldn’t keep training heavy while dieting. This is the typical bodybuilder excuse. That's all it is. Yes, your leverage won't be as great while dieting due to loss of fat and glycogen, but you should keep a record of max lifts while dieting so you have something comparable the next time around. You can either make the mental decision to put the fatigue and energy deficit aside and push through each workout like a champ, or you can throw in the towel on training hard before you even start. The choice is up to you. I say build some mental muscle while you conserve your physical muscle and you will be a much better lifter and/or bodybuilder because of it.