If you have ever traveled to Europe to places like Rome, you immediately notice the statues. I was in Rome recently and not once did I see a statue of a wimpy or skinny muscle-less man. I supposed with all the warfare of the time, the man without muscular tone was looked down upon as not very useful. It appears like every aspect of the man's body was muscular (if you know what I mean). So muscle building apparently was a requirement for the real man in ancient times.
We, of course, are a by-product of ancient Rome so the ideas of that time are still very prevalent in our day. I don't know many women that go completely ga-ga over a skinny man. Even with the evident man shortage many women are recognizing today, most will still prefer a nicely sculpted set of biceps and triceps any day over flab. Real men have always known the need to protect their women and children so keeping a fit physique was the most capable way of stopping threats to the man or his family. Muscles have no doubt always been a sign of a couple of things. While these signs aren't etched in stone, they do stand to reason why women love muscular men.
1. Strength. When a man has strong, muscular arms, most women can just imagine lying in them. I find a muscular man comforting in that he may be able to tackle some heavy lifting if I need such help. Nothing is more impressive that to see a man lift a heavy weight with the greatest of ease.
2. Sign of good health. Most women know that those muscle didn't come about by chance. The man with muscles obviously care enough about himself to make sure he is physically fit and hopefully will care that much about whoever he is dating to make sure good health is a priority for her too.
3. Sexy. Muscles look good. They make a man very easy on the eyes. It is nice to see the contrast between the female and male physique.