Into the Fold
The problem is, when the hamstrings are pushed to the limit of their flexibility, they rebel and avoid further stretching by either bending the knee or extending the hip. Hip extension means that as you sit on the floor, the short hams will pull the ischial tuberosities toward the back of the knees, which will tilt your pelvis backward, putting your spine into a major slump and flattening the natural curve of your lower back. The front body and internal organs—including the heart, lungs, and digestive organs—will be compressed, and the back of the body—including the back muscles and spinal ligaments—will overstretch. The tighter your hamstrings are, the more likely it is that this will happen. And that, in a nutshell, can be bad news for your back.
If you are bending forward and get pulled or pushed too far by a teacher or helper, you can seriously injure the spinal disks and ligaments. As you bend forward, more weight gets transferred to the front of the disks. With excessive force, the gel-like center of the disk can be pushed backward into the support ligaments, which can then bulge out. A bulging, or herniated, disk or an injured sacroiliac joint will disrupt your life and yoga practice for months, and may require expensive, time-consuming treatment.
There is a notable exception to the guidelines about low-back pain and forward bends: If your low-back pain is due to a swayback, you may actually find that forward bends ease your discomfort by stretching tight low-back muscles. The swayed, overarched, hyperextended lower back is usually caused by an anterior, or forward-tilted, pelvis, which is most often accom-panied by long, flexible hamstrings. So if you've got a swayback, you can usually move into the forward bend and find the back stretch pleasurable.
There's a simple way to check whether you might be vulnerable to low-back strain or injury in Paschimottanasana and other forward bends. First, lie on your back on the floor. Come into Supta Padangusthasana (Reclining Hand-to-Big-Toe Pose). Bring your right leg up, catch your foot with a strap, and straighten the right knee, while keeping the left leg straight on the floor. If you can make a 90-degree angle between your right leg and torso, you should be able to sit safely in Dandasana (Staff Pose). If you can't bring the leg to perpendicular (don't bend those knees!), your pelvis will tip backward in Dandasana, and you'll be sitting slumped before you've even tried to fold forward.!--page-->