Strictly speaking, intensity in the weight training context refers to the amount of work required to achieve the activity and is proportional to the mass of the weights being lifted - that is, how heavy the weight is relative to how strong you are.
Agents are deal makers, and they're really, really good at making deals. But they're also exceptionally helpful after the deal is made - agents act as a good intermediary between authors and publishers whenever disagreements come up.
I've often said that while gaining muscle can be very difficult, it's also pretty simple - at the heart of it, you just need to take in more energy than you expend, and use an intelligent program. This is especially true for beginners.