How to stretch?
The muscles are protected by a mecanism of reflex. Always that you stretch that reflex, this one will respond you sending a sign of contraction to the muscles for to avoid injuries. Therefore, when you stretch too much you are tautening the same muscles that you want to relax. This way to work it does pain and phisic deterioration, since, the musculars fibres it can to sprain, and later they can produce a elasticity gradual loss. This process can be prduced also when after a hard activity don't do the appropriate stretch. For all this, is very important to stretch always and to do it correctly.
REMEMBER: Always that you stretch, you have to do it in relax, without pain.