HEAD-TO-KNEE POSE
The main story in janu sirsasana is an asymmetrical stretch of the posterior kinetic chain, including the muscles at the back of the straight leg and the back itself. Two subplots contribute to the main stretch. One is the action of the bent leg and the other is the action of the arms. In the bent leg, the femur flexes, abducts, and externally rotates, drawing that side of the pelvis away from the straight leg. Although the main focus is on the extended leg, periodically bring your attention to the flexed knee. Look at the muscles that produce the positions of the hip and knee on this side. Engage these muscles to make the pose more active. Grasp the foot with the hands to link the shoulder and pelvic girdles, transmitting a stretch from the back into the leg. Connect the action of the bent leg with the same-side arm. For example, as the bent knee draws back, flex the same-side elbow more. This creates two counterbalancing forces with simultaneous movements in different directions. We saw this concept in the warrior postures, with the back foot constrained as the front of the body lunges forward. Observe the effect of flexing the trunk while moving the bent knee back. Note that when the trunk flexes, the muscles and ligaments of the back pull on the pelvis, tilting it forward. Similarly, as the femur flexes, the pelvis tilts forward. In this way, both the trunk and hip work together to affect the hamstring muscles of the straight leg. Conversely, the hamstring muscles, which pull on the ischial tuberosities, affect the orientation of the pelvis. As these muscles gain length, the lumbar spine flexes less and the pelvis tilts forward more.
Note how the bent-leg side of the trunk is longer than the straight-leg side. To balance this, flex the elbow on the bent-leg side to lengthen the trunk on the straight-leg side.
BASIC JOINT POSITIONS
The posterior kinetic chain links the muscles, tendons, and ligaments at the back of the body. Tightness in one muscle affects the position of the joints in other muscles; for example, tightness in the lower back can make it difficult to straighten the knees, and tightness in the hamstrings can make it difficult to flex the trunk. Identify areas of inflexibility and modify the pose to accommodate these regions. Then use facilitated stretching to create length in the muscles that limit mobility.
Bend the knee and use a belt if necessary to link the hands to the foot. As the muscles lengthen (take as much time as needed), straighten the knee. Use your physiological reflexes to gain length in the muscles and mobility in the joints. Work within your limitations, and do not force progress. Use the cradle pose to stretch the tensor fascia lata and gluteal muscles to create length to externally rotate the femur.
STEP 1 Activate the hamstrings to flex the bent-leg knee. The cue for this is to squeeze the lower leg against its own thigh. Flexing, abducting, and externally rotating the hip activates the sartorius. The psoas contributes an external rotation component to this movement.
STEP 2 The gluteals and tensor fascia lata work together in Janu Sirsasana. Squeeze the buttocks to engage the gluteus maximus. This externally rotates and extends the hip, drawing the bent knee back and down. Maintain joint congruency, especially in the knee. With this in mind, maintain the knee as a hinge and gain your rotation from the hip. Rotate the thigh and lower leg as one unit, like a log. Use the gluteus medius and tensor fascia lata to abduct the thigh out to the side, drawing the knee back and down.
STEP 3 Contract the quadriceps to straighten the knee. The tensor fascia lata helps stabilize the outer side of the knee and aids to flex the hip. Notice how the hamstrings relax and feel different in the stretch when you actively engage the quadriceps, their antagonist. Engage the peroneus longus and brevis muscles on the side of the lower leg to turn the foot out and open the sole.
STEP 4 Squeeze the torso against the thigh to engage the psoas. Activate the abdominals to flex and turn the bentleg side of the trunk. Experience how this action changes the feeling of the stretch in the lower back muscles, including the quadratus lumborum. This is a result of reciprocal inhibition. Note that when the femur flexes, the pelvis tilts forward—an example of coupled movement within the hip. Compare this with how flexing, abducting, and externally rotating the bentleg hip tilts that side of the pelvis back and down. Tilting the pelvis in opposite directions creates a “wringing” effect across the sacroiliac ligaments and produces a stabilizing bandha in this region.
STEP 5 Connecting the upper and lower extremities allows you to use the force generated by the arms to stretch the muscles of the back and lower leg. Contract the biceps and brachialis to bend the elbows and draw the trunk further over the leg. Flex the elbow more strongly on the bent-leg side to draw that side of the body more toward the extended leg, stretching the side of the body. If you are grasping the foot as shown, then pronate the forearms by pressing the mounds at the base of the index fingers forward. Engage the infraspinatus and teres minor muscles to rotate the shoulders outward. Fix the hands on the feet and attempt to raise the arms up. This contracts the anterior deltoids and draws the trunk deeper. Finally, draw the shoulders away from the ears by engaging the lower portions of the trapezius.
SUMMARY This orchestra of movement culminates in the characteristic stretch of Janu Sirsasana. The entire posterior kinetic chain stretches in this pose, including the erector spinae, quadratus lumborum, gluteus maximus, hamstrings, and gastrocnemius/soleus complex. The bent-leg quadriceps also stretch, and the back muscles on this side stretch more deeply than on the straight-leg side.