The name, head-to-knee pose, describes the fact that if the body’s flexibility allows, the whole of the torso will fold over the outstretched leg, with the head touching the knee or going beyond the knee, depending on the individual body’s proportions. As a result, it is sometimes called head-beyond-the-knee pose.
The asymmetry of the pose means that as well as being a forward bend, it also provides a slight spinal twist. Head-to-knee pose A is a good pose for creating the flexibility needed to progress into seated forward bend, where both legs are straight. In addition to stretching the hamstrings, it is also said to stimulate the kidneys and liver. It benefits the digestive system by stretching both the ascending and descending colon. This asana may be helpful for those suffering with headaches, fatigue, or menstrual pains; however, it should be avoided by anyone suffering from asthma, digestive or lower back issues.
Variation C also provides an effective stretch for the calf and ankle of the leg that is bent. It is a good preparation and complementary pose for half lotus pose. It requires more openness in the hip and length in the Achilles tendon than variations A and B.
This pose can be modified by sitting on blankets to lift the hips or placing blankets under the knee of the outstretched leg if tight hamstrings or knee pain is an issue. For those with more flexibility, the hands can clasp the edges of the foot or one hand can clasp the opposite wrist around the sole of the foot, with the head moving into the shin.