Due to the popularization of yoga, stretching as a tool for maintaining flexibility, mobility, and pain relief is all the rage. Unfortunately there are many dangers to self stretching and a lot of outdated information. This article will hopefully help you safely integrate stretching into your fitness routine.
First the dangers. There is evidence out there that yoga like stretching can be harmful if done incorrectly (not incorrectly according to yoga teachers, incorrectly according to your own body's structure). It can overstretch ligaments permanently, injure discs and other joints and block blood flow causing strokes. From my personal experience in zealous stretching, yoga and being passively stretched is that stretching may be just as dangerous as other rigorous activities. One example from my early days in Ashiatsu class was when a classmate was amazed how well my shoulders could stretch, kept stretching them and accidentally partially dislocated both my shoulders. Other overzealous self stretching has led to hip and sacroilliac dysfunction, as well as permanent ankle instability.
People who are naturally more lax can easily overstretch joints and ligaments making them unstable. People who are naturally more tight can tear muscles and tendons and even get a stroke from certain stretching positions that occlude blood flow.
In yoga and other stretching classes, teachers are prescribing stretches to a whole class en mass with only a little direction like "My shoulder is hurting.". But this is a major problem. Does she know why your shoulder hurts, does your shoulder need stretching or is it contraindicated, where does it need stretching, and do other people need shoulder stretches in the class, what if they already have lax shoulders due to dislocations or have different imbalances? It becomes quite a mess to address everyone's unique structure appropriately at once and what if the teacher doesn't even have training in therapeutic yoga? Are they just pretending they know what to do? Quite possibly.
If you are stretching beyond normal range of motion and overstretching areas that oh-so-satisfyingly can stretch a lot while stretching less or avoiding stretching all together in areas that are very tight, then you will set yourself up for injuries and pain due to increased structural imbalance. In other words, the cables holding your joint together become overly loose in one direction and your joint moves out of place, in motion or permanent dislocation. Also, if you try to stretch a muscle and you can't, you may end up dislocating or tearing another area that can stretch more easily. This is a common way people injure themselves in daily life. They can't move their hips so they strain their low back.
An aspect of stretching that is unknown to most teachers is that when you have adhesions in your fascia, joints, between muscles and bones, those patches of adhesion will be the last to stretch. That means say if you are trying to do the splits and your pectineus (an adductor muscles is adhered to the pubic bone) you may stretch all you want but the problem won't go away. The muscle and fascia may overstretch around it like a pin in a rubber band. If you stretch very slowly (over 10-30 minutes) and gently, you may start to mobilize the adhesions, but even then it depends on the strength of the adhesion. That's where myofascial release comes in. Your skilled massage therapist may be able to advance your flexibility much faster than stretching because they are taking off the bandages holding your tissues locked in place, specifically where they are immobile.
Now some people claim muscle tension/restriction is not in the fascia, its in the nervous system, ALWAYS, (There are nerves by the way in fascia.) However, Tom Myers who teaches in the second largest school of Rolfing still believes, despite a very open mind and evolving framework for bodywork, that science still supports the concept of dysfunction caused specifically by fascial adhesions. If you want to geek out on the science and learn some bodywork jargon. please check out his article "Can Fascia Stretch?" I have heard of multiple bodywork practitioners first hand releasing fascial adhesions on the dead (i.e. not a working nervous system) with some marked success.
Back to yoga stretching....Despite the pitfalls, yoga is much more than extreme stretching and gentle stretching plus strengthening, balance, breathing and meditation exercises can make major positive changes in your body whether its in yoga class or not. My grandfather who lived to be 95 and lived alone his last 15 years did gentle stretches every morning - touching his toes, opening and closing his fingers, etc. I thought these exercises were silly but now I realize they helped keep him mobile way beyond the age when most people are needing in home caregivers.
Best practices for safe and effective stretching
be very careful if you have loose joints
don't just stretch, strengthen - for some people, especially full-time office workers, you may need to strengthen much more than stretch
don't ever try to show off in class or elsewhere with your stretching abilities
don't do ballistic stretching, slower is better, and ballistic stretching leads to tears
if you have trouble not going with the class flow, consider using a dvd at home instead or trying a more yin class like for seniors
don't go beyond normal range of motion - it can be permanently disabling due to overstretching ligaments and dislocating joints
stop at the soft end feel and let your tissues melt rather than forcing it to the hard end feel
don't always do what your teacher says, take time out and meditate or relax when the stretch gives you any inkling of pain or discomfort, take note and do not attempt again without supervision
avoid types of stretches that put strain on joints, there's always a less risky way to stretch (examples: head and shoulder stands, lunges that put pressure on your knees, downward dog if you have any wrist pain at all)
avoid stretching a muscle in spasm - it can tear or go further into spasm (instead put the muscle into a contacted position passively or with isometric resistance)
see a physical therapist or highly experienced therapeutic yoga or pilates instructor to get a customized stretching and strengthening routine that addresses your specific imbalances
go slower and gentler than you think you need to - it takes much longer to stretch fascia for long lasting results
use your breath to help move into the stretch - focus on your belly and the out breath
if the stretch doesn't feel like it's doing anything, shift your angle a little to stretch different fibers of a muscle
notice if your whole body is moving in the stretch or if it's isolated to the joint you want to open, because usually you can achieve full range of motion if you are using your whole body but that's not that helpful if you are trying to stretch one joint
notice if emotions come up as you are stretching and look for the deep relaxing breath that comes naturally, which is a good time to move on
see your myofascial release or structural integration specialist to help balance your body and release fascial adhesions safely
do PNF stretching: using resistance from your hand, a band or a wall, isometrically contract the muscle that will be stretched for 10 seconds, then contract its opposing muscles for 10 seconds (resist in the opposite direction), then slowly stretch, repeat - this tricks your nervous system into safely letting go when you are dealing with more neuromuscular tension than adhesion
This is probably the most important point I will make here so pay attention. You don't need to stretch nearly as much if you integrate movement into your life. And movement will give you more balance as a lay person with little body knowledge than stretching will. Stretching is the band aid, movement is the preventative cure. See my last article.
If you have a desk job, I highly recommend learning qi gong, tai chi, or flow yoga, integrating it into your lunch break and getting up and moving once an hour with a reminder app on your computer. Then change your seating situation to something more dynamic like a kore stool, variable balans rocking kneeling chair, yoga ball and/or standing desk. If you have a hard manual labor job, you may need to do very different activities when not working (like don't play racquetball if you are a cook) and consider a yin yoga or qi gong practice that won't drain your energy or injure you.