How often? How long?

Stretching is done best when it is done to warm muscles. Post exercise, or after a hot bath or shower, you will get better results.

Holding a stretch for 20-30 sec enables the muscle to remember it's new legnth. A longer mor elastic muscle has way more stregnth, than a short, stiff muscle. Equate this to a rubber band....it will always shoot much farther across the room when it can be pulled back more and then let go. As well..the more hydrated your muscle is, the healthier it is, not unlike that dry brittle elastic. You don't want it to snap. On a side note: Did you know that when your achillies tendon snaps or breaks, it sounds like a shotgun going off? Fact.

Stretching should be done always after exercise, and as often as needed daily to maintain or gain a better flexability.