Matt Fitzgerald, the author of Brain Training for Runners, a book I highly recommend writes about the importance of hip mobility in his blog. He answers a question from a runner concerning why some runners seem to push-off more with their toes using extreme ankle flexion when running. Does a strong push-off create a faster runner?
Matt states that the ankle push-off is more a passive reaction to greater posterior hip extension. He writes that:
"Runners who exhibit extreme ankle plantar flexion at faster speeds are typically faster runners than those who exhibit moderate ankle plantar flexion, but it’s not because they push off the ground more forcefully through active calf muscle contraction. Rather, it’s because they have greater hip mobility. Indeed, a high degree of hip mobility, which enables runners to make large strides efficiently when running hard, is an often overlooked biomechanical characteristic of faster runners."
His suggestions to improve hip mobility include working on joint mobility exercises and a few all-out sprinting efforts during the week. I would also recommend getting a kickbike to work out the range of motion in your hips (as well as to have the most fun possible on two wheels!).
There are a few programs out there that focus on joint mobility. Most of these programs work on improving joint mobility. I use Scott Sonnon's "Ageless Mobility" and "Intu Flow" as well as Dr. Eric Cobb's Z-Health program. Z-Health is recommended as it works not only on joint mobility, but on reeducating the nervous system to use correct movement patterns.