Getting into the pose:

1. Sit with legs stretched in front and place hands behind the back on the mat. Drop head backwards,  stretch sternohyoid muscle to keep neck and throat relaxed.
2. Inhale, lift hips high. Push and extend feet into the floor

In the pose:

1. Contract transverse abdominis plus gluteus maximus, strengthen rectus femoris to support the lower body part and lift up hips as high as possible.
2. Stretch pectoralis major, anterior deltoid to keep chest open.
3. Contract trapezius and strenghthen brachialis to support the shoulder.

Variation:
From step 2, inhale and lift right leg straight up. Exhale and lower right leg. Inhale, change to lift left leg up.
Limitation:
If muscles at the legs and abdomen, chest are not strongly engaged,  knees will be bent, hips will be low and chest will be not open respectively.