Are there any exercises to stretch or strengthen a hip flexor?

Hip flexor stretches: Tight hip flexors make walking difficult and running painful because the tight hip flexor muscles make obtaining full hip extension impossible thus significantly shortening your stride and slowing your speed. Hip extension stretching will help stretch tight flexors. Anti-inflammatory medications such as Ibuprofen may also help. Once tight flexors are stretched, a strengthening program will help.

Absolutely: There are some good exercises to stretch a hip flexor. They all involve putting the leg or femur into extension in relation to the pelvis. Like putting the leg behind the pelvis and onto a table and lowering the pelvis. There are some good illustrations of this on the web. Do a search on "psoas" stretch or "hip flexor" stretch. Remember to go slowly.