For you to fully enjoy this pose and reap its benefits, two areas of the body need your attention. The four hamstring muscles are the first. Three originate at the back of the femur (thigh), and one originates at the ischial tuberosity (sitting bone) of the pelvis. Both heads of the biceps femoris (lateral hamstrings) attach to the outside of the knee region, while the semitendinosus and semimembranosus attach just below the inner knee. The four hamstrings work together to flex or bend the knee and to extend the hip joint, as they do when you're preparing to kick a ball.
To do Viparita Karani with the backs of your legs against the wall, your hamstrings must be somewhat loose. If you feel your hamstrings stretching in the pose, it will be more difficult to relax and to drop your tailbone down toward the ground. One way to overcome tight hamstrings in the pose is to do what was suggested earlier: Set up your bolster or blankets a bit farther from the wall. The other solution is to do a hamstring stretch or two before practicing Viparita Karani. If you are very tight, it may be sufficient to lie on the floor and draw one knee to the chest. But if you are like most students, you'll need to extend or straighten the knee while flexing the hip. The most effective hamstring stretches are those that both flex the hip and extend the knee: Adho Mukha Svanasana (Downward-Facing Dog Pose), Uttanasana (Standing Forward Bend), or Trikonasana (Triangle Pose). If you want, you can place a second bolster or two firmly rolled blankets between your legs and the wall to support them in the pose.
The Perfect Arch
The second area of the body to focus on in Viparita Karani is the spine. Some students complain of discomfort during backbending. This may come not from the backbend itself but from the unevenness of the backbend along the lumbar spine (lower back). If you are uncomfortable in backbending, you may not be relying on all five segments of your lumbar spine to move. Instead, you may be forcing the movement primarily at the lowest vertebral segments, the L4 and L5 joints.
For many students, Dhanurasana (Bow Pose) creates even backbends (see Posture Perfecter). To feel this sensation, lie on your belly on a comfortable surface. With an exhalation, bend your knees and hold your ankles while pressing your thighs into the floor. With the next exhalation, lift your shoulders and knees up to form the basket-shaped Dhanurasana. Keep breathing and note the sensation of your lower back bending evenly—this is the same sensation you're seeking for the lumbar spine in Viparita Karani.
If there is not enough arch in your spine when you do Viparita Karani, your pubic bone will be higher than your navel. With the body in this shape, the last one or two lower back ribs will not be on the bolster; they'll be hanging off so that the spine appears and feels flat. Make sure that when you position yourself on the bolster, your last rib or two are well supported by it. When you do this, your thoracic spine (upper spine) will arch, your breastbone will be lifted, and your breathing will be free. By supporting the thoracic spine's arch, you will create a moderate arch in the lumbar spine as well. To experience this sympathetic action of the thoracic and lumbar arches, sit comfortably on the edge of a chair with your knees bent and your feet about 14 inches apart; as you sit with a long spine, lift your breastbone as though you were going to drop back into Camel Pose. Notice how both your thoracic spine and lumbar spine arch evenly together. Now try to arch your thoracic spine without arching your lumbar spine. It will probably feel uncomfortable and unnatural. Apply this knowledge of spinal curvature to Viparita Karani.