I stated previously that lifting is the #1 thing you can do to improve your success with women, and I stand by that.
Yes, the physical side does help. But as mentioned by another poster, its the confidence that is the main effect. And don't forget testosterone.
The more you lift hard (compound exercises like squats and deadlifts), the more you are going to eat. The more you eat, the more testosterone you are going to produce. The more test you produce, the more attractive you will be to women.
I'm 5'10" and was 140 pounds coming out of high school. I hated being skinny so much that I let myself get fat - I was 215 lbs. by the time I was 27.
With diet and exercise, I got down to 150 lbs (and still had fat on me, yikes). Since then I've been lifting heavy and eating like a madman. I eat every 3 hours whether I'm hungry or not. I'm closing in on 175 lbs and I want to be 190 in the future.
I've been scrawny, I've been fat, and now I'm in shape. So trust me when I say it makes a huge difference with the women.
All you scrawny guys are kidding yourselves if you believe gaining muscle won't help you look and feel better, and be more confident.
Lifting heavy with compound exercises is WORK. Face it, most of us don't do physical work of any kind. Physical work makes you more of a man, no question.
Lastly, check your posture scrawnies! I know when I was scrawny it was just about impossible for me to stand up straight with my shoulders back because I had no back muscles. You need those back muscles to have the proper body language and posture.
really.
