One of the key elements of being flexible is to stretch warm. Never try to stretch cold. Though the body is always trying to maintain 98.6 degrees. 98.6 degrees is the bodies core temperature. Outer muscles and extremities are often much colder. That is why the doctor puts the thermometer inside your mouth. Well hopefully in your mouth only... ;-) Muscle, just like steel or glass, or any matter expands easier with heat.
In relation to endurance training, flexibility is important, so that if you fall off of your mountain bike at high speed your body can go into very flexible positions. If you are flexible, instead of tearing ligaments, muscle, or fascia your body will flex first. Does that mean you will never injure yourself? No, however you can decrease your chances dramatically by stretching. When we stretch it is important to understand that our main focus of stretch is not on ligament or tendon. The stretch’s focus is on the muscle and fascia. Fascia is the connective tissue that surrounds muscles and allows them to move freely over each other. Muscle and fascia can stretch up to 150 percent of its volume. Tendon only stretches about 4 percent of its volume.
Tendon attaches muscle to bone. Ligament is a bone-to-bone attachment and should not be stretched extensively. Ligament tissue is supposed to be strong. Like the wooden bar in a ballet class, which dancers use to stretch on. Would one try to make that stabilizer bar extremely flexible? No, it would not be able to support the weight of a dancer stretching on it. The bar should be a little flexible but not too much.
There is strength in yielding, as the Taoists would say. We know this all too well here in California, the earthquake capital of the world. Here buildings are built to flex and that prevents damage.
I recommend a 15-minute warm up, then stretching. In Yoga we warm up with about 7 sun salutations, then begin some mild stretching.
One of the key ways to know if you are stretching the wrong area is that your body will give a trigger pain. Typically this feels like a sharp electrical sensation.
Steven Earth Metz