Fitness increased my first night lays by around 40% (weight training). It also increased women coming up to me and initiating significantly.
I've always been either slender (6'3, 190 pounds) or muscular (6'3 210 pounds). I got plenty of women with runner's build (tight abs, lean look), but I get even more with a bulkier look and a little padding on the sides.
I have found fitness to be essential as I age, not only to prevent muscle loss and the "slumpy" look most men get, but to attract the kind of woman I'm attracted to. I'm in my early 40's, and I only date 20-somethings who are fit, open minded, sex-positive, and independent.
Current gf is 22, and moved in this weekend. Semi-open relationship. If I find another women I want to sleep with, I get a green light.
It's amazing what personal improvement all-around can do for your social life.