So now that I've revealed the big news...that muscles don't magically grow longer with stretching, let me do some explaining.
Most people think of muscles as being tight or loose (or open, or something similar). Tight usually means limited range of motion, loose/open meaning flexible. (Range of Motion is basically the ability to move at a joint.) To couple that, muscles can feel tight and be strong or feel tight and be weak, and vice versa, loose/open and strong, loose/open and weak. Review Jules' blog on "You Aren't Tight, You Feel Tight" is this is fuzzy. Does that make sense? In the end, we're more interested in joint range, i.e., where the joint end range is, in determining flexibility. We're also interested in having strength in that new flexibility, but more on that later.
Ex. A woman who runs every day in preparation for a race (please take days off when training, folks!) may have "tight" hamstrings. She doesn't cross train or stretch much, but does walk to work, and wears high heels, where she also sits at a desk for 6-8 hours a day. However, her hamstrings may be quite strong and "tight/short" in certain positions because they are propelling her action of running for hours a day. (And duh, her calves are shortened all day long, which doesn't help!)
A man who sits at a desk every day for 8 hours and then sits on his couch and watches TV after a one hour weight lifting workout (3 days a week) may also have "tight" hamstrings. However, his restriction may be due to adaptive shortening, in which "A muscle can change it's functional resting length to adapt to the length at which the muscle is habitually used or positioned." Thus, his hamstrings may be "tight" and weak, or at least much weaker than our woman.
So this "tight" hamstring thing is not necessarily just a muscle length issue for either person-it's also a range issue because neither of them are using full leg range of motion (and both of them sit...a lot!). So using the logic that Jules set forth about stretching , both folks would be benefited most by actually moving more diversely in more ranges of motion, or gaining strength in more range. What might that look like?
Both would be benefited by walking more often on varied terrain in minimalist/flat shoes (which uses the legs, hips, psoas, calves etc. in different ranges and impacts than running and chair sitting), lunging, squatting, and soft tissue work to break down adhesions (like ball rolling/foam rolling), as well as other movements too. Both would be benefited by moving to a dynamic desk (standing/floor sitting/etc), even if for an hour or two a day, in which legs would get the opportunity to be at full resting length, rather than consistently shortened by sitting in a chair, bent at ninety degrees. Our lady in training would benefit from adding cross-training movements to her running, and maybe taking a few days off to just walk, and did I mention ditch the high heels, especially at a standing desk and while walking? (And read here- I love my standing desk!)
*Time-out: the hamstring muscle group (semitendinosus, semimembranosus and biceps femoris) have a primary function of flexing the knee. So when the knee is bent, even if passively like in a chair, the hamstrings are passively shortened. Muscles' primary jobs are to move bones, and they work in agonist/antagonist relationships. The quads are knee extensors, i.e., they help to straighten out the leg, so constant sitting isn't helping your hamstrings or your quads. Take a moment to read a bit more and here's more info.*
So in case you don't care about hamstrings, let's look at musicians, for whom range is usually lost in the shoulders. Most of us use our arms in the same positions for hours a day without varying the weight or action, and we rarely reach or train overhead. One range that is often lost is the ability to flex one's shoulders, or basically reach arms overhead (like you would for a push-press or to prepare for a pull up). Adaptive shortening and weakness will often prevent good overhead position, which often equals rib thrust mania. (Or at least this is my problem) What might be a solution? Stretching isn't terrible (I've discussed some reasons to stretch before) to start, but using the full ROM is going to be most beneficial. Basically, ask yourself the question- what am I stretching for if I don't have strength in this new range of motion? If you think of a gymnast or figure skater, they have a huge range of motion, yet it's coupled with extreme strength and control in that large range of motion. If we just stretch for the heck of it and don't actually use that new range, it's not doing us any good (although it might feel nice).
If a musician like me (with limited overhead range) was a client that I was working with, I'd do some specific ball-rolling soft tissue massage work (targeting the supraspinatus and other rotator cuff muscles of the shoulder as well as the thoracic spine), and then see what the current range is. Rather than just stretching the shoulders, I'd instead start to move into flexion with a light weight (like a cork yoga block) and see what's possible (lying down to start with zero rib thrust). If someone has limited range but no injury, another activity could be hanging from a bar supported, perhaps feet on the floor. For the record, hanging from abar is quite hard, even if it's for 10-20 second increments and Katy Bowman suggests a very humane gradual progression to dead hanging especially if you don't have full range of motion in the shoulders, need to develop grip strength, or aren't ready to jump in on crazy Ido Portal hang/swing/one armed hang extravaganzas. Read more about it on Ido Portal's blog challenging daily dead hangs. In addition to helping develop some overhead strength in a range of motion most of us lack, it also feels great, especially if you're anchored at a computer or music stand most of the day! (Did I mention not to rib thrust when doing overhead work? We want to evaluate your shoulders, not your spine!)