It is said that the hamstrings harbour emotions steeped in ambition, such as greed, anger, competitiveness, and fear. These suppressed emotions are stored in the hamstrings and, over the years, are the source of the gradual stiffening and shortening of the muscles. For these reasons, releasing the hamstrings can be a long and psychologically arduous process. These stored emotions may arise with the intensity of physical sensation that we experience in the stretch. The natural tendency for many is to brace against these feelings, both emotional and physical, perpetuating the cycle of resistance and self-abuse. Instead, we must learn to release into the pose, to surrender to what is rather than force and strain to reach the feet. Gregor Maehle describes this process well in Ashtanga Yoga: Practice & Philosophy:
"All suppressed emotions are potentially crippling to our health: they are toxic and have an impact on our personality. It is essential that, if strong emotions do arise, we acknowledge whateve we feel and then let go of these emotions. Breathing through a posture requires that the stretch be kept at a manageable intensity. If the stretch is too strong we will harden and numb ourselves further. One needs to stretch with compassion and intelligence."Many students struggle to reach their feet in this pose and, in doing so, sacrifice the integrity of the spine, rounding the back and consequently straining the lumbar spine. Rather than rounding the back to stretch further, it is advisable to take a soft bend in the knees and lead with the sternum so that the lower back may release and lengthen while redirecting the stretch to the hamstrings. Alternatively or in combination with bent knees, placing a folded blanket beneath the sit bones to elevate the hips may be useful in finding extension in the lumbar spine by increasing the effect of gravity on the pose, which allows the abdominals and hip flexors, which may bunch and actually impede the fold if working too strongly, to soften and release allowing the hips to flex more completely.
Use the breath to carry you into the pose. With every inhalation, imagine the spine lengthening and the heart reaching to the toes. With every exhalation, soften and release to fold more deeply. Initiate the inhales at the base of the pelvic floor and direct your breath into the rib cage. Keep your mula bandha (root lock) and uddiyana bandha (navel lock) engaged to aid in the support and extension of the lumbar spine. There is a tendency to hunch the shoulders around the ears when we bind the arms in Paschimottanasana. This contraction in the neck and shoulders constricts the blood vessels in the neck and may result in headaches, red face, or dizziness. Rather than pulling with the trapezius, remember to keep the latissimus dorsi and serratus anterior engaged to pull the shoulders down, which then extends the thoracic spine and opens the heart. (You can actually see my giganto-lats quite clearly engaged in the picture above.)
Always be patient and compassionate with your body. If you practice the pose correctly with attention to detail, it is likely that you will not be able to fold as far as if you were to round the back and strain to reach the feet. Do not be bothered by this. When careful attention to alignment is used in practice of the asanas, the body develops and opens in a healthy and balanced way which prevents injury, builds strength, and paves the way for seamless entry into the more advanced postures.