The muscle named "piriformis" can be a major cause of sciatica—in fact modern chiropractic research suggests that piriformis syndrome accounts for up to 60% of all sciatica. Look up "piriformis syndrome": it is extremely common and can be utterly debilitating (Kit had this for more than six months at one point, and could not travel for more than 20' by car without having to get out and move around). Prolonged sitting is very often involved in this problem.
What many people do not know is that piriformis syndrome, if severe, can mimic all the symptoms of intervertebral disc impingement, including all the 'neurological deficits' (numbness around the buttocks, thighs, outer calf muscles; tingling and loss of feeling in the toes; and even loss of dorsiflexion, usually regarded as a very serious symptom).
Prudence and risk minimisation suggests that stretching piriformis is a sensible course of action before starting to look for other causes.
*Please note that all Stretch Therapy "stretching" techniques are also strengthening techniques, too, because we use isometric contractions as part of the process. The contractions strengthen the muscle in the part of the range of movement they are applied in, and if excessive tension is the cause of the pain you are experiencing, the same contractions result in a relaxation of the muscle.*
This exercise demonstrated here is one of the strongest you can try, and one of the most novel in terms of daily life movements. As well, it strongly affects the substantial fascia of the whole hip, including gluteus maximus. The advantage of this version is that you do not need a partner—all you need is something solid to hand on to.
Sharon is going to show the full version of how to do the most difficult of the piriformis stretches, but using a table, in place of a partner, as support. So, she's going to lie herself over the left knee first to get the back leg in a position, like so. And you'll notice also that she has her left hip on a cushion, which helps to tip her towards her front foot. She then reaches the back leg out as far as possible. And the first position she's going to go down into is simply to lay the center of her body over her leg, like this. This relieves a stretch on piriformis and also is a nice buttock stretch. Now that we've stretched the bottom muscle on the front leg, notice that the front knee has bent at 90 degrees.
Now, Sharon is going to lift herself away from the front leg up to full arms length, like so, and then turn to face her front foot, like this, and then draw herself as far forward as she can. Now, at this point here, she's going to reach one arm out towards the table, and assuming the table can't be moved, she'll then use that table to pull herself towards the front foot; breathe and relax. Now, in that position there, she does a contraction, which is to press the outside of the front foot straight into the floor. Five, four, three, two, one. She stops. She breathes in. She moves herself a little further to her right, and then, on a breath out, tries to take the center of her body straight down towards her foot, but while keeping her back straight. You're getting a decent stretch there, Sharon?
Okay. Breathe and relax. Breathe and relax. Now, to come out of this pose, you let go of whatever it is that you're hanging on to, and put that hand on the ground. And lift yourself out of that position with that hand. That's one of the best ways to do this exercise when you haven't got a partner. That's great.