Anantasana also called the Reclining Vishnu pose, is a beginner to intermediate level pose. It provides a nice stretch for the legs and also is a balancing pose in the reclining position.
Relax on your back in Shavasana for a few moments. Turn the body to your left. Keep the legs straight and the whole body in a single vertical plane. Stretch your left arm back, overhead. Bend the elbow and rest your head on the left palm. Bend the right knee and hold the right big toe with the index and middle fingers and the thumb. Slowly begin to stretch the leg straight and try to make it vertical. If you are unable to stretch the leg straight, you may like to use a strap to hold the foot and then try to stretch the leg. In the final position, you will notice a tendency to drop the foot forward and the hips backward. This will position the body at an angle. In the Anantasana, our effort is to keep the body in a single vertical plane with the right leg vertical and the left leg in a straight line with the buttocks and the shoulders. If you find it difficult to maintain the body in one line, you may keep a bolster behind your backfor support. As an experiment, you may also try to go against the wall and keep the entire back side of the body touching the wall while in the final pose. That will give you a good idea as to the placement of the legs and the buttocks. Maintain the final position for about ten breaths. Then release the leg down and rest in Shavasana for a few breaths. Now roll to your right and repeat the above steps on the other side.
It is a great pose for stretching the entire back side of the legs. Helps develop balance. Tones the thighs and abdominal muscles. Stretches the side of the body. Strengthens the shoulders. Improves blood (and oxygen) circulation in your heart and brain. Improves digestion.