Prasarita Padottanasana

This standing wide legged intense stretch, not only is a great stretching pose, but also will help headaches, fatigue, and mild depression.  The Banda will tone the deep abdominal organs and will relieve mild backaches.  It is a great basic standing pose, inverted symmetrical forward bend that almost all can do to their own ability.
Starting from Tadasana, you spread your legs apart 3 to 4 1/2 feet.  Place the hands on the hips and make sure your inner feet are parallel to each other.  Place the big tow firmly in to the floor.  engage the thigh muscles, inhale, and lift up with the chest.  Make the front torso slightly longer than the back.
Maintaining the length of the torso, lean froward from the hip joints.  Exhale and lock the core.  As your torso approached parallel to the floor, you can press your fingertips in to the floor directly below your shoulders and extend the elbows.  Move the spine evenly into the back torso.  The back should be slightly concave from the tailbone to the base of the skull.
Push your top thighs straight back to lengthen the front torso.  The inner groins should be pushed away from each other to open the pelvis.  Maintain the concavity of the back and the forward lift of the sternum and walk the fingertips between your feet.  Walk the fingertips between your feet.  If possible, lower yourself until your the crown of your head touches the ground in between your legs.  With each exhale lock the core and try to gently walk yourself a bit deeper.
This Asana will work the quadriceps and articulates genus, adductors, abductors, and the intrinsic and extrinsic muscles of the feet.  It will lengthen the adductors, hamstrings, spinal extensors, and gluteus maxims.
This is perhaps the safest, most accessible inversion in yoga.