One thing I'll add for the scrawny guys who can't seem to put on any weight. The ectomorphs.
From what I've found through my own personal experiences. Women like a guy who is fit and tone much more than a big bury guy who is stacked with muscle. What tends to happen in society is we all just associate fit guys with the ones who are stacked like a body builder. What's funny, is a lot of women are actually intimidated and repulsed by these guys. I'm a decent looking guy, but I'm small. I'm 6' tall and only 140lbs. But what I lack in body size I make up for by being incredibly tone and "ripped". For my entire life, I've struggled with weight. I just can't put it on. But what I've figured out, is I may not be able to build muscle, I can gain strength. Ectomorphic bodies don't build muscle the same way mesomorphs and endomorphs do. I have a very close friend who is a mesomorph. The guy drives a Beer truck and slings cases and kegs all day. Thus he's the typical egg head body builder looking guy. His arms are about as big around as my neck. But in an arm wrestle I can hold him steady.
I can't stand working out in a gym. Lifting weights, to me, is about as exciting as visiting a hospital. I just can't get into it. What I've found I love though, is rock climbing. What's great about this hobby is that is works with my body type so well. It's a whole lot easier for me to hold my 140lb self on an inverted wall with a two finger pinch than if I weighed 200lbs. It's also one of the best workouts you can do. There are a ton of crossfit guys who climb just because of the muscle control and core strength it builds. If you are an ectomorph looking to get strong and can't seem to actually build muscle. Get on YouTube and search climbing training videos. Even if you don't climb, these are awesome ways to work out and get sculpted without actually lifting weights.
And like I said, it's not at all about being big. It's about being fit.
Oh: One other thing. Climbing gyms and popular outdoor routs will introduce you to all sorts of great looking fit women. It's not like a normal gym where girls are out there working out, not wanting to be bothered. Everyone in the climbing community is really friendly and happy to just be out there doing their hobby. And there's never a bitch shield to deal with. It's really the perfect place to meet girls.
Edit: here's a picture of myself to show that I am not at all a big guy. But I do have a good amount of definition and muscle. I've been with quite a number of really hot, model quality women who said they found me very sexy.
