Tight hamstrings are an epidemic in the West, and with good reason: we sit WAY more than we were designed to. Anytime your knee is bent, your hamstrings are shortened, so all that time at your desk, behind the wheel, and watching tv is a continual (non)exercise in hamstrings shortening. If you participate in repetitive aerobic activity to counteract all that time seated (like jogging, hiking, or biking), then your hamstrings probably are not just short, but also tight and hard.
Tight hamstrings are not a character flaw, but they do have a host of negative repercussions. Your hamstrings, which actually consist of 3 muscles, attach to your sitting bones at the base of your pelvis and run down the back of your thigh, attaching to your lower leg bones below the knee. Tight hamstrings continually tug the back of your pelvis downward, creating postural misalignment. They can be a big culprit in low back pain, as well as rough on the knees. They also shorten your stride and impede your mobility.
Those are just some of the reasons that virtually every stretch program and yoga class includes some hamstrings openers. One of the most common is the forward fold, either standing or seated: bend forward, try to touch or hold your toes, and pull to go deeper. Ever done that?
Unless you already have open hamstrings, the forward fold is generally a bad idea.
Why? Since your hamstrings are connected to the base of your pelvis, when tight they prevent the pelvis from tipping forward. When you reach the limit of your hamstrings flexibility in a forward fold, which is almost immediately for a lot of people, your pelvis cannot move farther forward into the posture. However, as you continue to take your spine (which is connected to your sacrum) forward, you actively encourage (and in some cases, force) your sacrum to move forward while the rest of the pelvis stays stationary. Your SI joint is NOT designed to accommodate this motion (the sacrum and the pelvis should not move independently of each other), so you are courting SI joint misalignment and damage when you try to deepen a forward fold with tight hamstrings.
Additionally, your low back will round, putting a lot of pressure on the front of your lumbar discs, and encouraging them to bulge posteriorly. You may think you are opening your hamstrings with all your efforts to get your hands to your feet and your belly to your thighs, but you're really exposing your low back to potential injury if you are trying to deepen the fold with tight hamstrings. The moral of the story:
Forward folds are great if you ALREADY HAVE open hamstrings, but they are not the way to GET open hamstrings.
So, what should you do for your tight hamstrings? The safest and most effective hamstrings stretch is supta padangusthasna (reclining hand-to-big-toe pose):
If you have ever been to a yoga class, you've probably done supta padangusthasana. Why is it so great? When your back and sacrum are supported, and you move your leg into the posture, the action translates into a muscular stretch of the hamstrings. You're getting the result you seek (a lengthening of the fibres of the hamstrings) while simultaneously protecting your sacrum and low back. Total win-win.
Contrast with the forward fold, in which the legs are anchored (either against the floor or by virtue of being the standing root of the pose), and you move the torso, thereby vectoring the action into joints and discs (if you have tight hamstrings).
It's really a no-brainer: do supta padangusthasana often to safely lengthen your hamstrings! And incorporate these refinements to be sure you get the most out of the stretch:
1. Keep the down leg grounded.
With the right leg up, roll your inner left thigh towards the floor until your left knee and toes point straight up. Keep the back of the left thigh as close to the floor as possible. The down leg is your anchor and controls the depth of the stretch. If you let it go limp, then your pelvis will roll up as you draw the right leg deeper into the stretch. That means both ends of the right hamstrings will be moving away from the floor, so the hamstrings are not getting longer, and the posture loses its effectiveness.
2. Engage your quadriceps. Engage your quadriceps. Engage your quadriceps.
When you engage your right quadriceps (muscles on the front of the thigh), your right hamstrings get the message to let go (that release is what allows movement at the joints). You're actually hard-wired that way; it's called "reciprocal inhibition." When you engage your quadriceps in supta padangushtasana, your hamstrings are told to let go, and the stretch will move into the released fibres of the hamstrings, which is a good thing. If you don't engage your quadriceps, then the hamstrings don't get the message to let go, and the stretch will tend to go into the tendons and ligaments. Unlike muscles, tendons and ligaments have very limited elasticity, and overstretching them can create a host of ill effects.
Here's a practice awareness: if you feel supta padangusthasana (or any hamstrings stretch) behind your knee, the stretch is going into your tendons/ligaments, and you REALLY need to focus on quadriceps engagement and tip #4 below. This is a MUST for you. You should NOT feel the stretch behind your knee.
3. Move your outer hip away from your head.
When you take the right leg up into supta padangusthasana, your right hip will almost inevitably move towards your head. This will create some torque in your SI joint and will roll the hamstrings stretch more towards the inner thigh. To correct this universal tendency, press your outer right hip away from your head and towards your left foot until your hip bones are the same distance from the bottom of your mat (i.e., until your pelvis isn't cocked, even slightly, to one side.) This will take the torque out of the SI joint and focus the stretch in the centerline of the hamstrings.
4. Breath into the center of the hamstrings, and exhale to the ends.
All the other movements are really a set up for the real work, which is breath, intention and focus. With your right leg up (quadriceps engaged!), palpate the center of the back of your right thigh with your left fingertips. Try to find a knot of holding, or a bit of a bulge. (if you can't find that, just work at the approximate halfway point of the back of the thigh.) Slowly, deeply inhale into that spot, creating a feeling of openness and space. Then exhale from that central spot towards both ends of the hamstrings (the sitting bone at the bottom end, and the back of the knee at the top). You have to split your exhalation to make this work, sending it up and down the back of the thigh at the same time. Create openness with your inhalation, and length with your exhalation. Make the actions of the breath more focused and powerful with each breath cycle. This is where the magic happens, so don't waiver! Hold for a minimum of 6 breaths.
5. Know which way to push.
In addition to stretching the hamstrings, supta padangusthasana provides an opportunity to traction your hip joint. Tractioning the hip joint (when it's not weight-bearing) is an amazing antidote to the pressure of standing, and it's a great healer of the hip. When you are in your full expression of the pose, if the angle between the back of your up leg and the floor is less than 90 degrees, you should push from your hip into your heel. This will move the head of the leg bone a little away from the hip socket, and create the opening you are seeking. However, if that angle is more than 90 degrees, you need to push from the heel towards the hip to move the head of the leg bone away from the hip socket.
Pop quiz: in the picture above, which way should Letitia push?
She should push from the heel to the hip because the angle between the back of her right leg and the floor is greater than 90 degrees. That line of descent down the back of her right leg will move the head of her thigh bone away from the socket, and thereby create some space in her hip joint. If she pushes from the hip to the heel, she will be jamming the head of the thigh bone back up into the socket.
Make supta padangusthasana your friend. You really can't overdo this one, and it's a good idea to spend some time in it every day, using these great refinements.
Bonus video: 5 Tips for Using a Strap Effectively in Supta Padangusthasana: