Picture this scenario: You've been training your tail off for the past 4 months, trying to pack on as much muscle size as you possibly can. You've bulked up considerably and are quite happy with the size you've been able to achieve. There's just one problem... Along with all of that solid, lean muscle you've gained, you notice that you've also packed on some excess body fat in the process.
And no matter how "huge" you might be, nobody wants to walk around with a soft, smooth and flabby body. After most trainees have finished their "bulking" phase, they decide that it's time to "cut down" and strip off the excess body fat that they gained due to their high calorie, muscle-building diet. How do they usually go about this? They lighten up the weights and perform higher reps.
This has always been a widely accepted method of "cutting down" and if you ask most trainers in the gym they'll tell you that "heavy weights bulk up the muscle and lighter weights define the muscle". If someone told you that, and you tried to get ripped in that way, you now know something...that's not true.
It couldn't be farther from the truth. In fact, there is no logical basis for this way of training. No exercise will give you more definition than another. It is physically impossible to target fat loss from a specific area on your body. In other words, no excersice will magically burn fat off of your chest or cause it to appear more defined.
You can use the bench press, squat, standing curl, pull-up, military press, and deadlift to stimulate the most muscle growth. If you train with weights you will build muscle mass, it's really quite simple. Do you want to get ripped? Well, that's another story.
So how exactly do you "define" a muscle? The only way to "define" a muscle is by lowering your body fat percentage in order to make your muscles more visible. Body fat reduction can be achieved in two ways:
1) Modify your diet. You'll need to create a slight caloric deficit within your body to stimulate the fat burning process. This can usually be achieved by lowering your overall caloric intake to around 11-13x your bodyweight and focusing on consuming smaller meals more frequently throughout the day. This will keep your metabolism naturally raised at all times and will keep your body in a constant fat burning state.
2) Perform proper cardio workouts. Reduce your body fat simply by burning off all the excess fat you can. To maximize your body's fat burning capacity and also minimize the muscle loss that inevitably accompanies a fat burning cycle, focus on shorter, 15-minute cardio workouts performed 3-5 times per week at a high level of intensity.
That's all there is to it, folks. Take the notion of "light weight and higher reps" and throw it right out the window, down the street and around the corner. Following this misguided method will only cause you to lose muscle mass and strength, and will not assist you in burning fat or defining your physique.