Your body is comprised of a complex pulley system constructed of muscles and tendons. The first pulley system is made of up muscles able to pull and push joints and bones various directions. This is how you are able to bend your leg and straighten it again. Your muscles manage the entire strength and flexibility structure of your body and, no matter how inflexible you may be, your muscles are more than long enough to enable to bend in any direction, as far as you please. Inflexibility is engineered and controlled by the second pulley system: the tendons. Your tendons limit your ability to move your muscles in different directions by acting as a restraining system.
Stand up and try to do the splits with your legs. If you are reading this articles, chances are that you cannot. Even if you were able to do this, chances are that you could not get your legs completely straight in both directions. Now, you are feeling a pull on your inner thighs when you attempt to do the splits. These are not your muscles pulling your legs, this is the restraining system of your tendons. They act as elastic which restricts you from being able to use the full length of your muscles. Why is this so?
If your tendons did not exist and you were able to bend in any direction, no matter how much muscle mass you had, you would be prone to injury quite easily. If you had poor muscle mass and you fell down, the strength in your muscles would not prevent you from injury. Your weak muscles would be torn in the fall, because they would contract in preparation for the fall, but their strength would not uphold the force of your body, and your muscle would tear.
It takes a great deal of time for muscle to repair itself, and injury is likely to repeat itself if activity resumed before healing completes. Tendons, on the other hand, are made up of much more elastic tissue, the tissue is softer, and the healing takes a fraction of the time. If you pull or break a tendon, your muscles are still intact and the tendon heals quickly.
Your tendon pulley system allows flexibility based upon how much strength or muscle mass you have in your muscles. If you have great strength in all directions, then your tendon pulley system allows you to use the full length of your muscles, because if you were to fall, the muscle itself would be able to prevent injury by pulling taut and remaining strong. If you have poor muscle mass, then the tendon pulley system is aware of this and does not allow the muscle to be pulled or to tear. The tendons draw taut, and if further force is put on them, they are injured, but heal quickly.
Do not do stretching exercises before workout. Instead, train your muscles correctly with low weights and build up muscle mass in every direction, so that flexibility is gained naturally, rather than through barbaric stretching and holding of your elastic tendons. You know what happens when you stretch elastic out and hold it. It loses its ability to contract. If you do this to your tendons, they will be unable to protect your muscles, and you are likely to sustain far greater injury in the event of an accident.