Being a sports fan, I've noticed how many more professional athletes--specifically baseball players--seem to get hurt easier than they use to. The majority of them, however, are so much bigger than they use to be. Listening to one of my favorite pitchers of all time, Greg Maddux, I now completely understand why. It's not rocket science.
The answer he gave is true for everybody who exercises. Maddux explained that, whenever he was coming up as a baseball player, flexibility was a big thing. Today, during the home run era, strenght is the big thing. Players are strong, but less flexible; this is a big reason for more strained muscles and such.
Remember when you're exercising, always do a quick warm-up and stretch. While being strong and cut is cool, if you're constantly hurting it doesn't mean much. Just exercise smart.