This hip flexor stretch uses the same half-kneeling position that last week’s exercise described (used https://ascentpt.wordpress.com/2014/05/12/exercise-of-the-week-half-kneel-dorsiflexion-stretch/). Get into this position, with your hips and knees at 90 degree angles.
Tuck your tailbone under by engaging your abs. You should feel a stretch in front of the hip on the down leg (knee on the floor). You can use your hand as shown in the picture above to create extra stretch.
If you feel a stretch in this position, it is beneficial for you. Typically, ~10 degrees of hip extension is necessary for normal function (https://ascentpt.wordpress.com/2014/05/07/exercise-of-the-week-prone-hip-extension-stretch/)