This is a nice stretch for hip extension which critical joint mobility for efficient running. Most of us sit all day which shortens the iliacus, psoas, and hip flexor mechanism. To run with efficient elastic recoil, the upper leg most be able to extend behind the hips and naturally recoil forward.
Notice my fingers forward. this indicates that the direction of the ASIS- Anterior Superior Iliac Spine (bony things you feel on top of pelvis in front) should be forward at all times like headights. You do not want your pelvis to tilt forward (like a bucket spilling).
To do the stretch:
Start from a kneeling lunge.
Tighten your glutes in your back leg as you bend your front knee and stretch the hip flexors in your back leg
Make sure to keep your torso upright (don’t lean forward!). You should feel a stretch in the front of your hip, often this stretch continues into your abdomen.
Hold the stretch for 2 seconds and repeat 10 times with each leg.
You can also hold this stretch for 30 seconds for one or two times.
Please note this cautionary reminder: Never stretch before you run! Do this stretching drill after running or remote from running activity.