Tightness in the hamstrings can be a common symptom or finding for people with low back pain.  There are a few things that we need to look at to fully understand if indeed you have tight hamstrings.  

First, let's look at the anatomy of the hamstrings.  The hamstrings are made up of 3 muscles in each leg.  They are the Semimembranosus, Semitendinosus and the Bicep Femoris (which is split into two parts - Long head and short head).  Both the Semimembranosus and Semitendinosus are on the inside of your leg and the Bicep femoris is on the outside of the leg.  They run from your pelvis down past your knee.  Keeping it simple they are responsible for bending the knee and for extending the hip.

Next, let's look at what "normal" hamstring length is.  The easiest way to know if your hamstrings are indeed tight is to lay flat on your back with your arms by your side (palms up).  Keeping both your knees straight and your ankles dorsiflexed (pull your toes towards your knees) raise one leg up as high as you can without lifting the opposite leg off the ground.  This should not require a lot of effort.  If it does lift your leg as high as you can until your effort is increased.  If you are able to get your leg to 80° your hamstring is not tight.  

To be honest, if you can get your leg to 80° on both sides.  YOU DON'T HAVE TIGHT HAMSTRINGS! STOP STRETCHING THEM!

Finally, if you are not able to raise your straight leg easily to approximately 80° then it is time to address it.  A lot of times people will relate a sensation of tightness in the hamstring even though they are able to get their leg to 80°.  If this is the case, stretching is probably not the solution.  Also if you have been "stretching" your hamstrings for over several months and you are not making any head way then we will need to look at other solutions.  We will touch on these in future posts, so stay tuned.

Here are a couple basic mobilizations for the hamstring and/or posterior chain.

Hamstring Flossing.  

Perform it for 30 reps with 2-3 sec pause at the top.  As you try to straighten your knee also try to get your toe to touch your nose. We refer to the down leg as our difficulty dial.  The more bent the knee is the easier it is, the straighter the knee is the harder it is. 

Dynamic Leg Lowering

Perform it for 30 reps each leg.  Try to straighten the leg as soon as you can once you raise it to the top. Again, we refer to the down leg as our difficulty dial.  The more bent the knee is the easier it is, the straighter the knee is the harder it is. 

Doorway Leg Lowering

We are using a corner of a wall in this video but it is named after using a doorway to perform it.  Try to get your butt as close to the wall as you possibly can with keeping your straight leg straight at the knee.  From there perform 30 reps.  We call this a magic trick, bit of misdirection, your brain is thinking about the moving leg but the mobilization is on the up leg.

As with all mobility drills, these are to be done daily.  Do not skip a day, do not pass go.  Consistency is the key to changing the way that you move.