Lunge: The lunge could be done as either a static stretching or a dynamic strengthening exercise. As a stretch, the focus is on stretching the hip flexors of the back leg. As a strengthening exercise, the emphasis is on strengthening the leg straightening muscles.
Here are links to demonstration of the lunge – video 1
video 2 This link shows 3 simple lunge variations. In the first option, you raise and lower through a comfortable pain free range of motion, while maintaining your off-set foot position. In the second, you return to a standing position with your feet next to each other with each repetition. In the third, you lift your leg after you return to a standing position with each repetition creating more work for the hip flexors and a greater balance challenge.