Maybe you've had sand kicked in your face. Maybe you've lost one too many attainable women to beefier guys. Or maybe you've read so much about weight loss that actually admitting you want to gain weight is a societal taboo. Whatever the reason, you want to bulk up. Now.

But forget about your alleged high-revving metabolism, says Doug Kalman, R.D., director of nutrition at Miami Research Associates. 

"Most lean men who can't gain muscle weight are simply eating and exercising the wrong way," he says.

Here's your fix: Follow these 10 principles to pack on as much as a pound of muscle each week.

1. Maximize muscle building. The more protein your body stores-in a process called protein synthesis-the larger your muscles grow. But your body is constantly draining its protein reserves for other uses-making hormones, for instance. The result is less protein available for muscle building.