picture from www.laurensfitness.com
Think about it- runners use their hip flexors every step of the way. Run enough, and over time those muscles get tighter and tighter, which not only shorten stride but also contribute to low back strain, because believe it or not, they insert on the spine. Think about it- where else could a muscle required to lift your leg up be attached?
On top of that, if you routinely sit all day long, your hip flexors are put into somewhat of a permanent "shortened" position.
Tight hip flexors are common among runners and become more of a problem the older we get. The good news is they can be easily stretched several times a day without going the gym!
I found this website called laurenfitness.com, that illustrates some great ways to stretch your hip flexors. Lauren is a personal trainer from Australia who also happens to play professional volleyball in Europe.