All of the movements of the human body occur because of the variety of different types of joints in the body. No joint, no movement. That being said, the large majority of ailments occur because of the insult done to the joint in some way. While there are a variety of shapes and sizes, most of these joints operate in one common way; they have an end range and some level of “play” or laxity that is appropriate and needed for healthy, happy joints. While an appropriate level of “play” is good for the joint, too much is very not good and can lead to sprains and in extreme cases dislocations.
The joint is much better at operating within the limits of its range of motion. It does not as put as much stress on the tissues of the joint to walk, run, and move when done within the comfortable range of its motion. This is inevitably important for activities that push joints to their end ranges, often with significant forces. Take running, your heel hits the ground with force equal to your body weight times some number that depends on a number a variables, mostly speed, and that force is then transferred through your foot and capped off with a push from the lever that is your ankle. A short brief moment that may, or may not cross your mind that is done with such force and speed over and over again, is truly something nearly indistinguishable from magic.
Now if you have good ankle range of motion, this will not be a problem because this force production is occurring within a relatively small range of motion. But if you have tight calves and foot tissue, this high force production is going to be occurring over and over again at near end range of motion, putting higher stress on the tissues.
So, you say to yourself, sounds like if I just stretch enough I will be impervious to injury because my joints will bend so well due to my spending so much time to expand my joint’s range of motion to extreme limits with constant stretching. But as discussed earlier, too much play in the joint can lead to a laxity that can lead to more frequent shearing damage, potentially leading to early onset of osteoarthritis. The best option is a balance of both joint flexibility and joint integrity.
Okay, now that you have an understanding of the general principles of joint mobility; what does that mean, practically, to you? In regards to stretching; to increase the range of motion of any joint, the idea is to take yourself to the limit of comfortable of motion and hold your body there for an extended time to allow your body to adapt to that end range position. This gradual adaptation will allow your body to take joints to a further range without damaging the tendons, ligaments, or cushions that it is made of. This is a wonderful thing that will help us prevent popping off your achilles from your heel in a backyard basketball game and likewise. However, like I said earlier, a joint that is too flexible: not good. So how much stretching is too much stretching? That one is tough and is probably a little bit different for different people, but I will say in general if you do not stretch often, stretch more often. If you stretch constantly, stretch less often.
Work in between the end range of motion. That means do not put load (weights, extra gravity) on to your joints at the end of their range of motion available to you. Most successful lifting, running, and jumping is done putting large amounts of load across comfortable ranges of motion. The combination is the key to optimal force production that is needed for any kind of motion. What that means practically is, don’t squat with a bar on your back or over your head unless you really know what you’re doing, don’t do too much yoga, and don’t flex your spine too much when you bend over or pick something heavy off the ground.
Stretching is very important and generally good for you, but the true way to become less fragile is to have strong, AND flexible joints.