Hanumanasana (Splits Pose) is a challenging seated pose that requires the work of the hips and hamstrings, while balancing the upper body on the pelvis. With the hips and the legs moving in opposite directions, the hip flexors and hamstrings need to strong and flexible to attain the required balance and stability.
Ustrasana can be a very difficult pose for the neck, especially if your shoulders are tight. You can use a wall as a prop to protect your neck. Prepare for the pose with your back to a wall, with your toes turned under and your soles as close to the wall as possible. Exhale and lean back, as described in step 3 in the main description above. Press the crown of your head into the wall and, against this pressure, lift the shoulder blades deeper into your back. Keep your hands on your pelvis or swing them back to press your palms against the wall.
Beginners very often aren't able to touch their hands to their feet without straining their back or neck. First, try to turn your toes under and elevate your heels. If this doesn't work, the next thing to do is to rest each hand on a block. Position the blocks just outside each heel, and stand them at their highest height (usually about 9 inches). If you're still having difficulty, get a chair. Kneel for the pose with your back to the chair, with your calves and feet below the seat and the front edge of the seat touching your buttocks. Then lean back and bring your hands to the sides of the seat or high up on the front chair legs.