I remember taking a dance class when I was a little girl. We would always do floor exercises to warm up before dancing. My favorite was called Flying Butterfly. We'd sit down, facing the mirror of course, and put our feet together and our knees out wide. Then the teacher would say "Fly, butterflies, fly," and we'd flap our little knee wings.
Now we know that bouncing your body while you stretch is a big no-no. But why?
Bouncing can cause microtrauma in the muscle, which must heal itself with scar tissue. The scar tissue tightens the muscle, making you less flexible, and more prone to pain. This type of repetitive, bouncing stretch is called Ballistic Stretching and it can strain your muscles and tendons because they aren't quite warmed up yet.
Think of it this way. Your muscles are like bubble gum. If you stretch a cold piece of gum, it'll snap rather than stretch. Your muscles work the same way. They've got to be warmed up in order to be pliable.
Static Stretching, where you you hold one position for a period of time is much gentler on your body, because you ease your muscles into it. When you stretch, you want to work your edge, lengthening the muscle as far as you can, feeling a stretch, but NOT feeling pain.
Fit's Tips: Make sure you breath while you're stretching because holding your breath can increase your blood pressure, making you feel dizzy.