As we age, our hip flexors get tighter than when we were young. One way to combat this is to incorporate strength training into your routine. I met the folks at Crossover Symmetry at The Running Event in Austin this past year. They gave me a red Hip & Core System.
Hip & Core System
Apparently, the company makes three different hip and core systems in different colors. If you get the yellow one, that is the lightest resistance. The red, which I have, is for medium resistance and the blue is for strong resistance.