Think of your muscles as rubber bands. When you over-stretch a rubber band, it snaps. The same will happen to your muscles. So, when you’re stretching during warm-up, go as far as you can without straining. Breathe into the stretch for at least ten seconds, and then see if it will go a little further. Remember that you shouldn’t bounce when stretching, either. That only increases your chance of injury.
A warm up is intended to raise the body temperature and prepare a player physiologically and psychologically to compete in a competitive game. Research has suggested that the optimum duration of the warm up period, before flexibility or functional activities are undertaken, should be between 10 and 15 minutes. This should consist of a gradual increase in intensity. A warm up at this intensity has the effect of allowing an increase in the range of movement of the joints and improving aerobic performance, along with becoming more "flexible".
A warm up produces a 2 to 3 degree rise in body temperature that can last for 45 minutes. This increase in temperature leads to beneficial changes in body tissue:
The heating effect allows muscles and tendons to become more extensible. This makes stretching muscles and tendons easier and more effective. Research has suggested that this decreases the incidence of muscle strains.
There is an increase in blood flow, which means that there is an increase in oxygen to muscle tissue.
There is an increase in the temperature of the blood, which changes the partial pressure of blood gases. This means that more oxygen leaves the blood and enters muscle tissue.
The increase in temperature causes a rise in enzyme and metabolic activity. This improves the efficiency of muscle contraction.....