Things that shorten them, and things that don't lengthen them
Many people are under the impression that their hamstrings are too tight, like a pair of pants that shrunk in the wash. These three muscles run down the back of the thigh from the pelvis to below the knees and can wreck havoc in forward bends, or sitting on the floor with the legs straight. Otherwise, they are not much of a bother.
Other times, your hamstrings feel tight as a sensation. Regular massage and stretching doesn’t seem to change them in a permanent way.
So what is really going on with the hamstrings? Are they “tight?” What is a tight muscle anyway, and how does it get that way?
The hamstrings attach to your ischial tuberosity (sit bones) - if you sit upright on a hard chair, you will feel these two bumps on the bottom of the pelvis that you can sit up or rock back on. From there, they run down the back of the thigh, cross the knee and attach to the top of the lower leg, so they act on both the hip (extension) and knee (flexion).
When someone complains about tight hamstrings, I take an objective measurement to see if their hamstrings are short or normal. If they are short, they may not feel tight, because they are at their normal resting length, but they can be affecting range of motion of the hips and spine. My advice then is to stop shortening them all the time. Here’s a list of things that shorten your hamstrings:
The person who says their hamstrings feel tight is another story. It’s very hard to be objective when you are going by what something feels like. For example, hamstrings can feel tight even as they are actually being lengthened. For example, if you are doing downward dog the hamstrings are getting lengthened, but you can’t get your spine to come out of flexion so you pull on them even more (usually by dropping the heels and/or cranking the tailbone up with the back muscles). You’ll be in that position saying “my hamstrings are so tight!” but they are just at their end range. Forcing them is not going to make them less tight or result in longer hamstrings. You might even create excessive loads to the connective tissue (tendons) that attach the hamstrings to the sit bones causing proximal hamstring tears (a common yoga injury).
If your hamstrings feel sore, this is often interpreted as tight - for example, after a day when you’ve worked your hamstrings more than usual (weightlifting, climbing, squatting etc.). Or you've been sitting on the tendons for a long time, compressing them. Moving is great, go for a walk, but try not to obsessively tug on the hamstrings because they feel sore. They might be micro damaged and pulling on them might make the healing process take longer or result in more damage.
Ponder this: most of us have chronically short hip flexors (those muscles in the front of the hips) due to our habit of siting all the time, and then exercising on bikes and running or stepping or rowing etc, so much more flexion. But do they feel tight? If the muscles on one side of the joint are short and the other side long, what side is the sensational one? That's right; it’s the long side - the muscles getting pulled on are the ones you feel. So if you respond by stretching, it’s only potentially making the problem worse.
"If you go by sensation, you’ll just maintain the status quo."
Learn how to be objective about your ranges of motion and work diligently but safety to increase them if it’s warranted. Making these decisions based on how your muscles feel might be leading you down the wrong track, or even the road to injury.