"Heavy lifting won't make you bulk up!" We are hearing a lot of this phrase these days. Which is good, because it's true. But some people are still skeptical about it being true.
Why is it true? There is more than one component to gaining size. Lifting is a big component to that, but nutrition is just as important. The amount of food that we eat plays a major role in how big or small we are. If you want to gain 10 lbs of muscle, you have to feed your body enough extra food (calories) to make that happen. Our bodies can't make something out of nothing. 3,500 calories is the equivalent of one pound, whether losing or gaining. So to add 1 pound of muscle, you have to consume an additional 3,500 calories in your diet.
What will heavy lifting do to your body with your current diet plan? Lifting heavy and not adding extra calories to your diet will change your body composition which will change your metabolism, strengthen your muscles, and give you the definition you are really looking for. If you are just starting a weight training program, you are going to gain some muscle. As this is happening, you will most likely be losing fat at the same time. This is because you are changing your body composition to a higher percent of muscle. Don't worry about the scale here, take measurements. That initial muscle gain and fat loss could show the scale is not moving, but you are losing inches. This is a good thing. The more muscle your body has, the higher your resting metabolic rate is. You burn more just sitting there! As you continue with your weight training, you will notice gains in strength, in that you are able to lift more. This is where seeing real definition in areas of your body that didn't have it before comes in. It's also where your friends start saying, "Wow! You look amazing! What are you doing??"
So to sum it up, go big or go home. Well, don't go home, just throw some more weight on. :)