It can be a challenge to get a full hip extension in this pose. If the hamstrings and adductor Magnus are not strong enough, the gluteus maximus may do too much and pull the legs into external rotation; or the other adductors will activate to bring the knees together but also flex the hips, or the rectus femoris will work to extend the knees, but won’t fully extend the hips.

Spinal extensors, especially the lumbar, may try to help, but too much lumbar extension is not helpful, because it will limit hip extension by putting tension on the psoas complex.

The action in the arms is the same as the shoulder stand and viparita karani the action in the hips and legs is the same as for lifting into urdhva dhanurasana.

All in all, considering the many muscle actions that must be balanced for this pose to work, sustaining this basic posture actually requires a high degree of coordination.