Janu Sirsasana- Seated Head to Knee Posture

This videos has different variations, please modify at your pace.

This refers to seated forward bend, stretching the head to the knee would be the literal meaning of what the Sanskrit words suggest. But to my practical understanding, its effectiveness goes beyond the target of the head to the knee, as one progresses. It's about lengthening out the spine without limitations, though with care and respect to your flexibility range at the moment.
The posture involves the lubrication of the knee as one would have to bend in the knees on each side accordingly to place the sole of each on the inner thigh of each leg. The entire body is an interconnected system of different components, but then the major target here is pin pointedly around the back, moving away from the lower back, as one would have to pull in the abdomen and pelvis.
This beautiful posture has different variations that also impact effectively on the sides, working to expound the capacity of the lungs, the rib cage, the side neck, arms, and hips. A very good sequence to improve respiratory issues, cold, and sciatica pains. In this particular sequence, the pelvic floor is also at work, as you move into the alignment, you have to pull, and tighten up the pelvic to engage your root chakra and the epigastric plexus or sacral chakra. This will internally work effectively on the reproductive system.
Outlined points of benefits: Relive tension around the Hamstrings, groins, hips, back and the spine. Good posture to relief sciatica pains, menstrual pains, although with care. This posture stimulates the digestive system against constipation and poor digestion. The pancreas also gets stimulated to regulate blood sugar level, very good to manage diabetes, liver and kidney problems. Different variations of this posture will also clear pains around the side neck and ribs.