Originally Posted by AdelaaR

I'll tell you why.
When I started cycling 3 years ago it turned out that I'm apparently "the muscular type".
This resulted in my arms staying quite thin and my legs becoming disproportionally big.
One year of triathlon, and the swim training that goes with it, has already greatly reduced this.
My arms are twice as muscular as they were last year.

I have nothing against specialized sports, but specialized athletes often don't look very healthy and balanced.
Skinny marathon runners and huge muscular discus throwers come to mind.
Multi-sporters, on the other hand, are the most complete and balanced athletes.
Have a look at some decathletes ... man do those guys (and girls) just look friggin' great!
Their sport forces them be balanced.