This article is from the Stretching FAQ, by Brad Appleton Brad_Appleton@ivhs.mot.com with numerous contributions by others.
For front splits, the front leg should be straight and its kneecap should
be facing the ceiling, or sky. The front foot can be pointed or flexed
(there will be a greater stretch in the front hamstring if the front foot
is flexed). The kneecap of the back leg should either be facing the floor
(which puts more of a stretch on the quadriceps and psoas muscles), or out
to the side (which puts more of a stretch on the inner-thigh (groin)
muscles). If it is facing the floor, then it will probably be pretty hard
to flex the back foot, since its instep should be on the floor. If the back
kneecap is facing the side, then your back foot should be stretched out
(not flexed) with its toes pointed to reduce undue stress upon the knee.
Even with the toes of the back foot pointed, you may still feel that there
is to much stress on your back knee (in which case you should make it face
the floor).
 
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