Roger Cole’s reply:
Forward bends teach patience. It takes a long time to enter them deeply. Enlightenment does not necessarily occur when the head reaches the legs, so there is no need to get it there soon, if ever. The realization of yoga is to be fully conscious, present, and content at whatever stage of the practice you have attained. Paradoxically, when you are truly satisfied right where you are, your pose often opens up and you can easily move forward.
The physiological explanation for this may lie partly in the stretch reflex. This reflex causes a stretched muscle to automatically contract in opposition to the stretch. If you try too hard to bend forward, you trigger stretch reflexes in your hamstring muscles. You feel stretching pain and cannot bend further into the pose. Pushing yourself deeper into the pose just makes matters worse. The more pain you feel, the stronger the stretch reflex.
One way around this is to stop moving deeper into the pose as soon as you feel a slight challenge, long before you reach the point of pain. At this point, hold your position constant for a long time, without pushing into or backing out of the pose. Keep your knees straight and don’t lose your pelvic tilt. You will find that, without moving, you get more and more comfortable right where you are. This most likely means that the stretch sensors (muscle spindles) in your muscles are getting reset, so that what formerly felt like a stretch to them now feels neutral. At this point, you feel comfortable in a position that previously felt like a challenge, so it’s easy to feel satisfied where you are. The paradox is that by maintaining this sense of neutrality, your stretch sensors will most likely become ready to allow you to move deeper into the pose (without causing pain or a strong muscle contraction). You are ready to move to a new point of challenge and wait there, repeating the cycle.
The most important alignment points in Uttanasana (Standing Forward Bend) are to fold as much as possible at the hip joints (tilt the top rim of the pelvis forward) and to lengthen the front of the body as much as you can, so the spine only rounds over a little. If you pull the head toward the legs without tilting the pelvis or lengthening the spine enough, the spine rounds too much and you can injure your lower back or sacroiliac joints. Even folding at the hip joints has its dangers-if you push too hard, you can tear a hamstring muscle or tendon.
Regarding hyperextension, if your knees straighten past 90 degrees, you don’t want to force them any further. However, forward bends pull on the hamstring muscles, and this tends to bend the knees, providing some protection against hyperextension.
If you are in good physical condition and your alignment is good, one way to progress in forward bends is to vigorously practice standing postures, with a strong Uttanasana between each posture. Standing postures like Utthita Trikonasana (Extended Triangle Pose), Utthita Parsvakonasana (Extended Side Angle Pose), and Virabhadrasana I, II, and III (Warrior 1, 2, and 3) work well. Do each standing posture twice on each side. Hold each pose (including Uttanasana) for 30 seconds to one minute. But don’t do this practice six days a week-three or four is plenty.
Again, don’t be in a hurry. I know one yoga teacher who struggled with forward bends for about 20 years with little progress. Past age 60, she eased up substantially on her practice and her forward bends suddenly progressed dramatically. She still cannot put her head on her legs, but she is happy. Which is more important?