Commonly called a "hardgainer", you have a "high metabolism" that doesn't allow you to gain weight very easily. When you exercise, you may end up actually losing weight and your routine may end up making you stronger, but not any bigger. When you do gain muscle, it says bye-bye as soon as you stray from a solid training and diet program. In order to pack on some solid lean muscle that doesn't disappear the first time you skip a protein shake, your training has to be...