If you’ve ever had an injury at your hamstring injury, you will know about it! You’ll go from comfortable forward bending one day to dramatically restricted, often painful forward bends the next day. This injury occurs where the tendon of the hamstring muscle knits into the membranous lining of the bone, the periosteum. In this case it is where the periosteum covers the ischial tuberosity or sit-bone. Often this is not a tear of the tendon itself but an avulsion, where the periosteum has been pulled or torn away from the bone. This injury can, of course, happen to varying degrees and brings pain and stiffness in forward bends.
If you especially feel discomfort in wide-legged forward bends it is most likely the hamstring portion of the adductor magnus muscle where it inserts onto the sit-bone that is injured rather than one of the hamstrings themselves. Unfortunately, this is a common injury in yogis and one of the reasons we recommend that students not be adjusted in wide-legged forward bends, eg Upavishta Konasana. As you can imagine, in these postures the adductor magnus is being asked to stretch as an adductor on the inner thigh as we widen our legs as well as a hamstring muscle on the back of the leg as we flex forward.
There are a couple of possible reasons why the muscle insertions at the sit-bones are so susceptible to injury. The main one seems to be when ones practice is dominated by straight-legged forward bends. Especially when standing the insertions at the sit-bones are under the large load of the entire upper body as we fold forward. A flexion-dominant practice also tends to weaken the hamstring muscles. This is due to the reciprocal inhibition , where the activation of the hip flexor muscles means that the extensor muscles (of which the hamstrings are one) are inhibited or switched off. In standing forward bends the extensor muscles are working eccentrically, i.e., against gravity. This helps a muscle to strengthen more effectively, however, at the same time it also places greater stress on the muscle, which makes it more prone to injury.
Whether the injury is in the periosteum, the tendon, the hamstring or the hamstring portion of the adductor magnus muscle the same therapy protocol will apply. The therapy needed to enable this injury to quickly heal is to take stress off the insertion and strengthen the extensor muscles, especially the hamstrings. In standing forward bend postures this is easily done by bending or at least softening the knees on entering and exiting forward bends. The deeper you bend your knees the faster your extensor muscles will strengthen. The other benefit of this method is that all your leg and lower trunk muscles must work together synergistically and a natural balance and harmony of strength of all the leg and lower trunk muscles is achieved. This is why squatting is an ideal strengthening movement and a very functional one that we can incorporate into our daily lives, not just our practice. I recommend doing this with different stance lengths: feet together, hip-width apart, wide apart and everything in between! Specifically in postures like Trikonasana and Parshvottanasana you can activate and strengthen your hamstrings by drawing your leading foot back towards the other foot, without moving the feet. If you find that you are unable to avoid pain at the ischial tuberosity (sit-bone) in any of the standing forward bends then omit practicing them until the injury has healed sufficiently.
In seated forward bends you can activate the hamstrings by pressing the heels of your feet down into your mat. This turns your stretch into a more regulated stretching method called Post Isometric Relaxation or PIR. PIR is when the receptors in your tendons (golgi tendon organs) sense how much pull is being exerted onto the tendon by the contraction of the muscle. After being activated by muscle contraction these receptors then signal the muscle to relax. These very receptors are in charge of monitoring the amount of muscle contraction that happens and protecting the tendons wherein they reside. Stretching in this way helps to balance strength with flexibility and thereby is not only a very effective method of stretching but is also very safe, especially when self applied. Additionally, pointing the feet in forward bends seems to relieve some stress off the sit-bones.
Of utmost importance is when you arrive in the forward bend that you do then straighten out your legs. This stretches the entire length and belly of the muscle (the reason you are doing a forward bend) and most importantly, takes the stress of the insertion at the sit-bones. To keep the knees bent once in the forward bend will transfer the tension of the stretch back up to the hamstring insertion at the sit-bone instead of distributing it over the whole muscle. With this injury it is better to not go as deeply forward with your trunk but instead to keep the legs straight. The enemy here is not stretching the hamstrings per se. Instead we want to reduce the stress upon the insertion at the sit-bone.
Worth noting is that there is a difference between an inhibited muscle and a weak muscle although both with appear to be weak. Inhibition is a neurological state, which can be due to the antagonist muscle being contracted (here the hip flexors) equating to reciprocal inhibition or otherwise from an imbalance of the position of the pelvis. This pelvic torsion usually results in one-sided weakness and would preferably require therapy to correct quickly. In this case the muscle is not inherently weak but appears so due to its handicapped position. On the other hand, weak hamstrings take longer to restore to strength although both will benefit greatly from strengthening movements and postures.
For a speedier recovery focus on some specific postures that target strengthening the hamstrings, eg: Shalabasana and Purvottanasana. Also very effective is a one-legged Purvottanasana. This will further challenge your hamstrings and also highlight for you the comparative strength of your hamstrings from right to left.
Overall, what is important is that in you remove the stress from your hamstring insertion and at the same time strengthen these muscles. Bending your knees, like transiting through a squat, on entering and exiting your forward bends will aid both of these goals. In your forward bends ensure that you are using all your leg muscles and not just your hip flexors, which will inhibit and thereby weaken your hip extensors. Additionally, adding in some postures that target hamstring strength will speed up your recovery. With this simple protocol I have had students heal their long-standing sit-bone pain within a few weeks. Left untreated this injury can take between one and two years to heal! Wishing you a speedy recovery back to pain-free forward bends.
 Reciprocal inhibition is when activation of one muscle (the agonist) inhibits the action of the antagonist muscle, relaxing it and allowing us to effectively stretch it.