The answer to the original question posted depends on what kind of body type you are and whether you have a fast or slow metabolism.
If you have a fast metabolism and find it hard to gain muscle weight, stop doing all cardio and concentrate on heavy weights, low reps. When you get to the size you want to be, then return to cardio to get definition. It's almost impossible to bulk up and cut up at the same time. Even if you're on a strict diet, when you bulk up, some of the weight goes to your waist. Accept the waist increase until your bulk up, then resume cardio and start cutting up.
If you have a slow metabolism and have to watch your weight, do LOTS of cardio and light weights and high reps. You can get big doing light weights. It just takes more time than doing heavy weights.
Here are more tips from another one of my web sites:
"People often ask me for workout tips on line and in person. Here are two that will transform your body. I promise.
I used to be thin and found it impossible to gain a pound no matter how much I stuffed myself. Here are my "Before & After" pix. The "Before" pic is scary!
Then I read Arnold Schwarzenegger's 1978 autobiography. It was mostly inane drivel, but the last chapters contained incredible workout routines. I found his "forced reps" especially useful. Before I started doing forced reps, people told me I had a swimmer's body. A few months after I started doing forced reps, guys at the gym would ask me if I were getting ready for a contest!
This is what forced reps are: For your last set of bench presses, ask a passerby to spot you. Pack on so much weight you can only do one rep by yourself. Then have the spotter "force" or help you do an additional three or four reps. Then look in the mirror! The pump is so dramatic after even one set of forced reps you won't recognize the stranger staring back at you in the mirror. I am not exaggerating. You can also do forced reps with the military press, preacher bench curl (the best exercise for bulking up AND defining your biceps), lat pull-downs on the machine and my personal bete noire, squats. (yechh!)
Conversely, if you have to watch your weight and merely looking in the refrigerator seems to add five pounds to your frame, THE best way to speed up your metabolism, burn fat and NEVER diet again is kickboxing or any other form of martial arts. You will also never spend another boring minute on the treadmill or Stairmaster either. And you won't run to your car on a dark street, clutching your keys so you can jump in fast, afraid of muggers.
Kickboxing is an incredible cardio workout. Martial arts (boxing, Tae Bo etc.) are a big yuppie fad right now and many gyms offer free classes. Check out the gyms in your area.
I punch and kick the bag on the second floor of Gold's Hollywood twice a week for an hour each time without taking a break. That's like doing 10,000 reps with a light dumbbell. No amount of light weights/high reps will cut you up like that. Every so often, I see competitive bodybuilders staring at me at the gym. I'm certain they're asking themselves, "What steroid is he doing that I'm not that makes him so ripped?" Sometimes, they come up to me and ask me that question in a roundabout way!
I'll get off my soapbox now. See you at the gym!"