Protect the Hamstrings in Forward Bends
What you are feeling is probably a partial tear in one of the two short tendons that connect the hamstring muscles to the sitting bone. It may be right at the bone, at mid-tendon, or at the junction where the tendon merges into the muscle. If the injury is old, chances are you are working not only with tendon, but with scar tissue as well.
The anatomy of this injury is quite simple. You have three hamstring muscles. The upper end of each of them attaches to the sitting bone (ischial tuberosity). Two of the hamstrings (semitendinosus and biceps femoris) share a single, short tendon that joins them to the sitting bone. The third (semimembranosus) has its own short tendon. The lower ends of all three hamstrings attach just below the knee. When these muscles contract they bend the knee and extend the hip joint. To stretch them effectively, a student must simultaneously straighten the knee and flex the hip joint.
This is just what happens in Uttanasana and other straight-legged forward bends: the knee straightens and the hip joint flexes. This moves the sitting bone away from the back of the knee and lengthens the hamstring muscles. Hamstrings are strong muscles, so it can take a lot of force to stretch them. When the force is more than the tendon can bear, the tendon partially tears at or near the sitting bone. (Other types of hamstring injuries are also possible, including mild or severe damage to muscle, tendon, or bone caused by strong, hard muscle contraction. This article will focus only on mild or moderate partial tears of a hamstring tendon caused by over-stretching.)
In order to protect your students from an injury in a hamstring tendon, you need to understand what puts them at risk for such injuries. Stretching too hard is an obvious factor. It is especially likely to cause injury if you physically push a student into a stretch, so be sure to avoid this.
Stretching too fast, without proper awareness, can also lead to injury. When a student stretches too quickly, it can cause a reflex contraction of the hamstrings which makes the muscles that are supposed to lengthen shorten instead. Students whose muscles are both strong and tight are especially at risk for this kind of injury.
Stretching while cold may increase risk, because a cold tendon is less flexible and has less blood flow than a warm one. But stretching while hot and fatigued (for example, at the end of a long, vigorous workshop) may also be risky. The heat may make the connective tissue in the tendon so flexible that its molecular structure can be torn apart by vigorous stretching. In addition, the fatigue makes it more difficult for the student to monitor and control the degree of stretch.
Another major risk factor is weak hamstring tendons. This is often a result of habitual over-stretching and insufficient strength of the hamstring muscles (weak muscles and weak tendons go together, because activities that strengthen the muscles also strengthen the tendons). Habitual overstretching comes from an excessive practice of daily forward bends with insufficient recovery time in between. This can break down collagen molecules (the building blocks of the tendon) faster than the body can replace them. Yoga teachers are especially at risk for this, because they often maintain a strenuous personal practice and also demonstrate forward bends day after day in their classes.
Stretching unevenly can also place a hamstring tendon at risk. For example, if the semimembranosus muscle is significantly tighter than the other two hamstrings, its tendon will receive most of the stretching force that would normally be distributed evenly among all three hamstrings. Likewise, certain combinations of rotation and bend at the hip or knee joints can focus excessive stretch on a small part of a hamstring tendon, or can pull a tendon at an angle that tends to separate it from the sitting bone.
One of the most frustrating things about a hamstring tendon injury near the sitting bone is that it persists for so long. Tendons have a much poorer blood supply than muscles, so when you tear them, they heal much more slowly. Students very often try to stretch their way out of the injury too soon, too hard, or too often. This not only slows the healing process, it also produces excessive scar tissue. Scars don't stretch well, so later stretching in the same area can put excessive strain on the intact tendon fibers surrounding the scar, causing additional injury. This, in turn, produces more scar tissue, leading to a vicious cycle of progressively worsening injury.
The healing process after a tendon tear can be roughly divided into three phases: inflammation, repair, and remodeling. By understanding what happens in each of these stages, you will be better prepared to give your students advice on what to do and when to do it.
When a student first tears a tendon, many of the tiny blood vessels (capillaries) that feed it are destroyed. During the first 72 hours after injury (the inflammation phase), the body's main job is to stop bleeding, clear away damaged tissue, prevent infection and lay the ground work for later repair. Stressing the area with stretching or strengthening exercises during this time will only further tear the tendon and its capillaries, undoing much of the work the body has done and making the injury more severe.
If the inflammation phase is allowed to run its course without disturbance, the body will enter the repair phase, which lasts six weeks or so. It begins this phase by setting up a delicate molecular and cellular matrix that serves as the framework for reconstructing capillaries and connective tissue. It then starts the initial stages of filling in this matrix.
A healthy tendon is made of collagen fibers arranged in an orderly way, making it strong and somewhat flexible in the direction of pull applied to it. However, at the beginning of the repair phase, the body lays down new collagen fibers haphazardly. This is a crucial time. If the student systematically applies very mild force along the lines of the healing tendon (by practicing extremely gentle strengthening and stretching asanas), the collagen matrix will become aligned in an appropriate way. The body will then lay down new fibers of the right type and connect them to one another in the optimal orientation to produce a strong, slightly flexible tendon. If, instead, the student does not apply any stress to the tendon after the body lays down the initial collagen fibers, the body will continue to lay down new fibers haphazardly, and connect them randomly. The result will be a weak, thick, inflexible scar.
Another potential problem might arise if the student stresses the healing tendon too much by practicing asanas that demand more than just a little stretch or contraction of the hamstrings. If that occurs, the matrix will break down, the tendon may tear more, and the student will be thrown back to square one of the healing process (inflammation), quite possibly with a more severe injury than the original one.
The people who have the hardest time avoiding excessively stretching an injured hamstring are yoga teachers themselves. Many yoga teachers instinctively feel that they can "stretch their way out" of the injury, so they do too much too fast. They are often reluctant to give up the vigorous practice they love and the busy teaching schedule that earns their livelihood. They feel that to teach properly, they must demonstrate hamstring stretches to their students. Even those who back off from strong hamstring stretches at first often re-introduce them as soon as they start feeling better, which is usually too soon.
Of course, the best way to deal with hamstring injuries is to prevent them from happening in the first place. There are many ways to do this. The most important is to never push your students into hamstring stretching poses. The second most important is to instruct students never to push themselves to the point of pain at the sitting bones, especially in forward bends. Instead, help your students develop strong, stretch-tolerant hamstring tendons by systematically including asanas that strengthen the hamstring muscles in both the shortened and lengthened positions (see How to Recover from Upper Hamstring Tendon Injuries). When students are cold, start them with warming poses, including mild hamstring stretches such as Adho Mukha Svanasana (Downward-Facing Dog), before more extreme hamstring poses. Guide students to stretch consciously, and urge them to use extra care when their muscles are hot or fatigued. Teach good alignment to build tendon strength and flexibility in the desired direction and to distribute the stretching load evenly over the hamstrings tendons rather than focusing it on a single spot.
If a student has a known hamstring injury, or if you suspect one because she feels pain at or near the sitting bone in forward bends, urge her to immediately stop doing any pose that creates the pain and strictly follow the recovery advice. Advise her that such injuries must be taken seriously and "babied" for at least several months before she should return to a full practice. Finally, if you are dealing with this problem yourself, take heart. With patience and diligence, there is hope for hamstrings.
Read about How to Recover from Upper Hamstring Tendon Injuries.
Roger Cole, Ph.D. is an Iyengar-certified yoga teacher (http://rogercoleyoga.com), and Stanford-trained scientist. He specializes in human anatomy and in the physiology of relaxation, sleep, and biological rhythms.